rev 15544 : imported patch fold_select

   1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
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   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
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  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  25 
  26 package java.lang.invoke;
  27 
  28 import jdk.internal.org.objectweb.asm.ClassWriter;
  29 import jdk.internal.org.objectweb.asm.Opcodes;
  30 import jdk.internal.reflect.CallerSensitive;
  31 import jdk.internal.reflect.Reflection;
  32 import jdk.internal.vm.annotation.ForceInline;
  33 import sun.invoke.util.ValueConversions;
  34 import sun.invoke.util.VerifyAccess;
  35 import sun.invoke.util.Wrapper;
  36 import sun.reflect.misc.ReflectUtil;
  37 import sun.security.util.SecurityConstants;
  38 
  39 import java.lang.invoke.LambdaForm.BasicType;
  40 import java.lang.reflect.Constructor;
  41 import java.lang.reflect.Field;
  42 import java.lang.reflect.Member;
  43 import java.lang.reflect.Method;
  44 import java.lang.reflect.Modifier;
  45 import java.lang.reflect.ReflectPermission;
  46 import java.nio.ByteOrder;
  47 import java.security.AccessController;
  48 import java.security.PrivilegedAction;
  49 import java.util.ArrayList;
  50 import java.util.Arrays;
  51 import java.util.BitSet;
  52 import java.util.Iterator;
  53 import java.util.List;
  54 import java.util.Objects;
  55 import java.util.concurrent.ConcurrentHashMap;
  56 import java.util.stream.Collectors;
  57 import java.util.stream.Stream;
  58 
  59 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
  60 import static java.lang.invoke.MethodHandleNatives.Constants.*;
  61 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
  62 import static java.lang.invoke.MethodType.methodType;
  63 
  64 /**
  65  * This class consists exclusively of static methods that operate on or return
  66  * method handles. They fall into several categories:
  67  * <ul>
  68  * <li>Lookup methods which help create method handles for methods and fields.
  69  * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
  70  * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
  71  * </ul>
  72  *
  73  * @author John Rose, JSR 292 EG
  74  * @since 1.7
  75  */
  76 public class MethodHandles {
  77 
  78     private MethodHandles() { }  // do not instantiate
  79 
  80     static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
  81 
  82     // See IMPL_LOOKUP below.
  83 
  84     //// Method handle creation from ordinary methods.
  85 
  86     /**
  87      * Returns a {@link Lookup lookup object} with
  88      * full capabilities to emulate all supported bytecode behaviors of the caller.
  89      * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
  90      * Factory methods on the lookup object can create
  91      * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
  92      * for any member that the caller has access to via bytecodes,
  93      * including protected and private fields and methods.
  94      * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
  95      * Do not store it in place where untrusted code can access it.
  96      * <p>
  97      * This method is caller sensitive, which means that it may return different
  98      * values to different callers.
  99      * <p>
 100      * For any given caller class {@code C}, the lookup object returned by this call
 101      * has equivalent capabilities to any lookup object
 102      * supplied by the JVM to the bootstrap method of an
 103      * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
 104      * executing in the same caller class {@code C}.
 105      * @return a lookup object for the caller of this method, with private access
 106      */
 107     @CallerSensitive
 108     @ForceInline // to ensure Reflection.getCallerClass optimization
 109     public static Lookup lookup() {
 110         return new Lookup(Reflection.getCallerClass());
 111     }
 112 
 113     /**
 114      * Returns a {@link Lookup lookup object} which is trusted minimally.
 115      * It can only be used to create method handles to public members in
 116      * public classes in packages that are exported unconditionally.
 117      * <p>
 118      * For now, the {@linkplain Lookup#lookupClass lookup class} of this lookup
 119      * object is in an unnamed module.
 120      * Consequently, the lookup context of this lookup object will be the bootstrap
 121      * class loader, which means it cannot find user classes.
 122      *
 123      * <p style="font-size:smaller;">
 124      * <em>Discussion:</em>
 125      * The lookup class can be changed to any other class {@code C} using an expression of the form
 126      * {@link Lookup#in publicLookup().in(C.class)}.
 127      * but may change the lookup context by virtue of changing the class loader.
 128      * A public lookup object is always subject to
 129      * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
 130      * Also, it cannot access
 131      * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
 132      * @return a lookup object which is trusted minimally
 133      */
 134     public static Lookup publicLookup() {
 135         // During VM startup then only classes in the java.base module can be
 136         // loaded and linked. This is because java.base exports aren't setup until
 137         // the module system is initialized, hence types in the unnamed module
 138         // (or any named module) can't link to java/lang/Object.
 139         if (!jdk.internal.misc.VM.isModuleSystemInited()) {
 140             return new Lookup(Object.class, Lookup.PUBLIC);
 141         } else {
 142             return LookupHelper.PUBLIC_LOOKUP;
 143         }
 144     }
 145 
 146     /**
 147      * Performs an unchecked "crack" of a
 148      * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
 149      * The result is as if the user had obtained a lookup object capable enough
 150      * to crack the target method handle, called
 151      * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
 152      * on the target to obtain its symbolic reference, and then called
 153      * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
 154      * to resolve the symbolic reference to a member.
 155      * <p>
 156      * If there is a security manager, its {@code checkPermission} method
 157      * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
 158      * @param <T> the desired type of the result, either {@link Member} or a subtype
 159      * @param target a direct method handle to crack into symbolic reference components
 160      * @param expected a class object representing the desired result type {@code T}
 161      * @return a reference to the method, constructor, or field object
 162      * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
 163      * @exception NullPointerException if either argument is {@code null}
 164      * @exception IllegalArgumentException if the target is not a direct method handle
 165      * @exception ClassCastException if the member is not of the expected type
 166      * @since 1.8
 167      */
 168     public static <T extends Member> T
 169     reflectAs(Class<T> expected, MethodHandle target) {
 170         SecurityManager smgr = System.getSecurityManager();
 171         if (smgr != null)  smgr.checkPermission(ACCESS_PERMISSION);
 172         Lookup lookup = Lookup.IMPL_LOOKUP;  // use maximally privileged lookup
 173         return lookup.revealDirect(target).reflectAs(expected, lookup);
 174     }
 175     // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
 176     private static final java.security.Permission ACCESS_PERMISSION =
 177         new ReflectPermission("suppressAccessChecks");
 178 
 179     /**
 180      * A <em>lookup object</em> is a factory for creating method handles,
 181      * when the creation requires access checking.
 182      * Method handles do not perform
 183      * access checks when they are called, but rather when they are created.
 184      * Therefore, method handle access
 185      * restrictions must be enforced when a method handle is created.
 186      * The caller class against which those restrictions are enforced
 187      * is known as the {@linkplain #lookupClass lookup class}.
 188      * <p>
 189      * A lookup class which needs to create method handles will call
 190      * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
 191      * When the {@code Lookup} factory object is created, the identity of the lookup class is
 192      * determined, and securely stored in the {@code Lookup} object.
 193      * The lookup class (or its delegates) may then use factory methods
 194      * on the {@code Lookup} object to create method handles for access-checked members.
 195      * This includes all methods, constructors, and fields which are allowed to the lookup class,
 196      * even private ones.
 197      *
 198      * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
 199      * The factory methods on a {@code Lookup} object correspond to all major
 200      * use cases for methods, constructors, and fields.
 201      * Each method handle created by a factory method is the functional
 202      * equivalent of a particular <em>bytecode behavior</em>.
 203      * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
 204      * Here is a summary of the correspondence between these factory methods and
 205      * the behavior of the resulting method handles:
 206      * <table border=1 cellpadding=5 summary="lookup method behaviors">
 207      * <tr>
 208      *     <th><a name="equiv"></a>lookup expression</th>
 209      *     <th>member</th>
 210      *     <th>bytecode behavior</th>
 211      * </tr>
 212      * <tr>
 213      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
 214      *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
 215      * </tr>
 216      * <tr>
 217      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
 218      *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
 219      * </tr>
 220      * <tr>
 221      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
 222      *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
 223      * </tr>
 224      * <tr>
 225      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
 226      *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
 227      * </tr>
 228      * <tr>
 229      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
 230      *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
 231      * </tr>
 232      * <tr>
 233      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
 234      *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
 235      * </tr>
 236      * <tr>
 237      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
 238      *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
 239      * </tr>
 240      * <tr>
 241      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
 242      *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
 243      * </tr>
 244      * <tr>
 245      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
 246      *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
 247      * </tr>
 248      * <tr>
 249      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
 250      *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
 251      * </tr>
 252      * <tr>
 253      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
 254      *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
 255      * </tr>
 256      * <tr>
 257      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
 258      *     <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
 259      * </tr>
 260      * <tr>
 261      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
 262      *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
 263      * </tr>
 264      * <tr>
 265      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
 266      *     <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
 267      * </tr>
 268      * </table>
 269      *
 270      * Here, the type {@code C} is the class or interface being searched for a member,
 271      * documented as a parameter named {@code refc} in the lookup methods.
 272      * The method type {@code MT} is composed from the return type {@code T}
 273      * and the sequence of argument types {@code A*}.
 274      * The constructor also has a sequence of argument types {@code A*} and
 275      * is deemed to return the newly-created object of type {@code C}.
 276      * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
 277      * The formal parameter {@code this} stands for the self-reference of type {@code C};
 278      * if it is present, it is always the leading argument to the method handle invocation.
 279      * (In the case of some {@code protected} members, {@code this} may be
 280      * restricted in type to the lookup class; see below.)
 281      * The name {@code arg} stands for all the other method handle arguments.
 282      * In the code examples for the Core Reflection API, the name {@code thisOrNull}
 283      * stands for a null reference if the accessed method or field is static,
 284      * and {@code this} otherwise.
 285      * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
 286      * for reflective objects corresponding to the given members.
 287      * <p>
 288      * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
 289      * as if by {@code ldc CONSTANT_Class}.
 290      * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
 291      * <p>
 292      * In cases where the given member is of variable arity (i.e., a method or constructor)
 293      * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
 294      * In all other cases, the returned method handle will be of fixed arity.
 295      * <p style="font-size:smaller;">
 296      * <em>Discussion:</em>
 297      * The equivalence between looked-up method handles and underlying
 298      * class members and bytecode behaviors
 299      * can break down in a few ways:
 300      * <ul style="font-size:smaller;">
 301      * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
 302      * the lookup can still succeed, even when there is no equivalent
 303      * Java expression or bytecoded constant.
 304      * <li>Likewise, if {@code T} or {@code MT}
 305      * is not symbolically accessible from the lookup class's loader,
 306      * the lookup can still succeed.
 307      * For example, lookups for {@code MethodHandle.invokeExact} and
 308      * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
 309      * <li>If there is a security manager installed, it can forbid the lookup
 310      * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
 311      * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
 312      * constant is not subject to security manager checks.
 313      * <li>If the looked-up method has a
 314      * <a href="MethodHandle.html#maxarity">very large arity</a>,
 315      * the method handle creation may fail, due to the method handle
 316      * type having too many parameters.
 317      * </ul>
 318      *
 319      * <h1><a name="access"></a>Access checking</h1>
 320      * Access checks are applied in the factory methods of {@code Lookup},
 321      * when a method handle is created.
 322      * This is a key difference from the Core Reflection API, since
 323      * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
 324      * performs access checking against every caller, on every call.
 325      * <p>
 326      * All access checks start from a {@code Lookup} object, which
 327      * compares its recorded lookup class against all requests to
 328      * create method handles.
 329      * A single {@code Lookup} object can be used to create any number
 330      * of access-checked method handles, all checked against a single
 331      * lookup class.
 332      * <p>
 333      * A {@code Lookup} object can be shared with other trusted code,
 334      * such as a metaobject protocol.
 335      * A shared {@code Lookup} object delegates the capability
 336      * to create method handles on private members of the lookup class.
 337      * Even if privileged code uses the {@code Lookup} object,
 338      * the access checking is confined to the privileges of the
 339      * original lookup class.
 340      * <p>
 341      * A lookup can fail, because
 342      * the containing class is not accessible to the lookup class, or
 343      * because the desired class member is missing, or because the
 344      * desired class member is not accessible to the lookup class, or
 345      * because the lookup object is not trusted enough to access the member.
 346      * In any of these cases, a {@code ReflectiveOperationException} will be
 347      * thrown from the attempted lookup.  The exact class will be one of
 348      * the following:
 349      * <ul>
 350      * <li>NoSuchMethodException &mdash; if a method is requested but does not exist
 351      * <li>NoSuchFieldException &mdash; if a field is requested but does not exist
 352      * <li>IllegalAccessException &mdash; if the member exists but an access check fails
 353      * </ul>
 354      * <p>
 355      * In general, the conditions under which a method handle may be
 356      * looked up for a method {@code M} are no more restrictive than the conditions
 357      * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
 358      * Where the JVM would raise exceptions like {@code NoSuchMethodError},
 359      * a method handle lookup will generally raise a corresponding
 360      * checked exception, such as {@code NoSuchMethodException}.
 361      * And the effect of invoking the method handle resulting from the lookup
 362      * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
 363      * to executing the compiled, verified, and resolved call to {@code M}.
 364      * The same point is true of fields and constructors.
 365      * <p style="font-size:smaller;">
 366      * <em>Discussion:</em>
 367      * Access checks only apply to named and reflected methods,
 368      * constructors, and fields.
 369      * Other method handle creation methods, such as
 370      * {@link MethodHandle#asType MethodHandle.asType},
 371      * do not require any access checks, and are used
 372      * independently of any {@code Lookup} object.
 373      * <p>
 374      * If the desired member is {@code protected}, the usual JVM rules apply,
 375      * including the requirement that the lookup class must be either be in the
 376      * same package as the desired member, or must inherit that member.
 377      * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
 378      * In addition, if the desired member is a non-static field or method
 379      * in a different package, the resulting method handle may only be applied
 380      * to objects of the lookup class or one of its subclasses.
 381      * This requirement is enforced by narrowing the type of the leading
 382      * {@code this} parameter from {@code C}
 383      * (which will necessarily be a superclass of the lookup class)
 384      * to the lookup class itself.
 385      * <p>
 386      * The JVM imposes a similar requirement on {@code invokespecial} instruction,
 387      * that the receiver argument must match both the resolved method <em>and</em>
 388      * the current class.  Again, this requirement is enforced by narrowing the
 389      * type of the leading parameter to the resulting method handle.
 390      * (See the Java Virtual Machine Specification, section 4.10.1.9.)
 391      * <p>
 392      * The JVM represents constructors and static initializer blocks as internal methods
 393      * with special names ({@code "<init>"} and {@code "<clinit>"}).
 394      * The internal syntax of invocation instructions allows them to refer to such internal
 395      * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
 396      * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
 397      * <p>
 398      * In some cases, access between nested classes is obtained by the Java compiler by creating
 399      * an wrapper method to access a private method of another class
 400      * in the same top-level declaration.
 401      * For example, a nested class {@code C.D}
 402      * can access private members within other related classes such as
 403      * {@code C}, {@code C.D.E}, or {@code C.B},
 404      * but the Java compiler may need to generate wrapper methods in
 405      * those related classes.  In such cases, a {@code Lookup} object on
 406      * {@code C.E} would be unable to those private members.
 407      * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
 408      * which can transform a lookup on {@code C.E} into one on any of those other
 409      * classes, without special elevation of privilege.
 410      * <p>
 411      * The accesses permitted to a given lookup object may be limited,
 412      * according to its set of {@link #lookupModes lookupModes},
 413      * to a subset of members normally accessible to the lookup class.
 414      * For example, the {@link MethodHandles#publicLookup publicLookup}
 415      * method produces a lookup object which is only allowed to access
 416      * public members in public classes of exported packages.
 417      * The caller sensitive method {@link MethodHandles#lookup lookup}
 418      * produces a lookup object with full capabilities relative to
 419      * its caller class, to emulate all supported bytecode behaviors.
 420      * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
 421      * with fewer access modes than the original lookup object.
 422      *
 423      * <p style="font-size:smaller;">
 424      * <a name="privacc"></a>
 425      * <em>Discussion of private access:</em>
 426      * We say that a lookup has <em>private access</em>
 427      * if its {@linkplain #lookupModes lookup modes}
 428      * include the possibility of accessing {@code private} members.
 429      * As documented in the relevant methods elsewhere,
 430      * only lookups with private access possess the following capabilities:
 431      * <ul style="font-size:smaller;">
 432      * <li>access private fields, methods, and constructors of the lookup class
 433      * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
 434      *     such as {@code Class.forName}
 435      * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
 436      * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
 437      *     for classes accessible to the lookup class
 438      * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
 439      *     within the same package member
 440      * </ul>
 441      * <p style="font-size:smaller;">
 442      * Each of these permissions is a consequence of the fact that a lookup object
 443      * with private access can be securely traced back to an originating class,
 444      * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
 445      * can be reliably determined and emulated by method handles.
 446      *
 447      * <h1><a name="secmgr"></a>Security manager interactions</h1>
 448      * Although bytecode instructions can only refer to classes in
 449      * a related class loader, this API can search for methods in any
 450      * class, as long as a reference to its {@code Class} object is
 451      * available.  Such cross-loader references are also possible with the
 452      * Core Reflection API, and are impossible to bytecode instructions
 453      * such as {@code invokestatic} or {@code getfield}.
 454      * There is a {@linkplain java.lang.SecurityManager security manager API}
 455      * to allow applications to check such cross-loader references.
 456      * These checks apply to both the {@code MethodHandles.Lookup} API
 457      * and the Core Reflection API
 458      * (as found on {@link java.lang.Class Class}).
 459      * <p>
 460      * If a security manager is present, member and class lookups are subject to
 461      * additional checks.
 462      * From one to three calls are made to the security manager.
 463      * Any of these calls can refuse access by throwing a
 464      * {@link java.lang.SecurityException SecurityException}.
 465      * Define {@code smgr} as the security manager,
 466      * {@code lookc} as the lookup class of the current lookup object,
 467      * {@code refc} as the containing class in which the member
 468      * is being sought, and {@code defc} as the class in which the
 469      * member is actually defined.
 470      * (If a class or other type is being accessed,
 471      * the {@code refc} and {@code defc} values are the class itself.)
 472      * The value {@code lookc} is defined as <em>not present</em>
 473      * if the current lookup object does not have
 474      * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
 475      * The calls are made according to the following rules:
 476      * <ul>
 477      * <li><b>Step 1:</b>
 478      *     If {@code lookc} is not present, or if its class loader is not
 479      *     the same as or an ancestor of the class loader of {@code refc},
 480      *     then {@link SecurityManager#checkPackageAccess
 481      *     smgr.checkPackageAccess(refcPkg)} is called,
 482      *     where {@code refcPkg} is the package of {@code refc}.
 483      * <li><b>Step 2a:</b>
 484      *     If the retrieved member is not public and
 485      *     {@code lookc} is not present, then
 486      *     {@link SecurityManager#checkPermission smgr.checkPermission}
 487      *     with {@code RuntimePermission("accessDeclaredMembers")} is called.
 488      * <li><b>Step 2b:</b>
 489      *     If the retrieved class has a {@code null} class loader,
 490      *     and {@code lookc} is not present, then
 491      *     {@link SecurityManager#checkPermission smgr.checkPermission}
 492      *     with {@code RuntimePermission("getClassLoader")} is called.
 493      * <li><b>Step 3:</b>
 494      *     If the retrieved member is not public,
 495      *     and if {@code lookc} is not present,
 496      *     and if {@code defc} and {@code refc} are different,
 497      *     then {@link SecurityManager#checkPackageAccess
 498      *     smgr.checkPackageAccess(defcPkg)} is called,
 499      *     where {@code defcPkg} is the package of {@code defc}.
 500      * </ul>
 501      * Security checks are performed after other access checks have passed.
 502      * Therefore, the above rules presuppose a member or class that is public,
 503      * or else that is being accessed from a lookup class that has
 504      * rights to access the member or class.
 505      *
 506      * <h1><a name="callsens"></a>Caller sensitive methods</h1>
 507      * A small number of Java methods have a special property called caller sensitivity.
 508      * A <em>caller-sensitive</em> method can behave differently depending on the
 509      * identity of its immediate caller.
 510      * <p>
 511      * If a method handle for a caller-sensitive method is requested,
 512      * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
 513      * but they take account of the lookup class in a special way.
 514      * The resulting method handle behaves as if it were called
 515      * from an instruction contained in the lookup class,
 516      * so that the caller-sensitive method detects the lookup class.
 517      * (By contrast, the invoker of the method handle is disregarded.)
 518      * Thus, in the case of caller-sensitive methods,
 519      * different lookup classes may give rise to
 520      * differently behaving method handles.
 521      * <p>
 522      * In cases where the lookup object is
 523      * {@link MethodHandles#publicLookup() publicLookup()},
 524      * or some other lookup object without
 525      * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
 526      * the lookup class is disregarded.
 527      * In such cases, no caller-sensitive method handle can be created,
 528      * access is forbidden, and the lookup fails with an
 529      * {@code IllegalAccessException}.
 530      * <p style="font-size:smaller;">
 531      * <em>Discussion:</em>
 532      * For example, the caller-sensitive method
 533      * {@link java.lang.Class#forName(String) Class.forName(x)}
 534      * can return varying classes or throw varying exceptions,
 535      * depending on the class loader of the class that calls it.
 536      * A public lookup of {@code Class.forName} will fail, because
 537      * there is no reasonable way to determine its bytecode behavior.
 538      * <p style="font-size:smaller;">
 539      * If an application caches method handles for broad sharing,
 540      * it should use {@code publicLookup()} to create them.
 541      * If there is a lookup of {@code Class.forName}, it will fail,
 542      * and the application must take appropriate action in that case.
 543      * It may be that a later lookup, perhaps during the invocation of a
 544      * bootstrap method, can incorporate the specific identity
 545      * of the caller, making the method accessible.
 546      * <p style="font-size:smaller;">
 547      * The function {@code MethodHandles.lookup} is caller sensitive
 548      * so that there can be a secure foundation for lookups.
 549      * Nearly all other methods in the JSR 292 API rely on lookup
 550      * objects to check access requests.
 551      */
 552     public static final
 553     class Lookup {
 554         /** The class on behalf of whom the lookup is being performed. */
 555         private final Class<?> lookupClass;
 556 
 557         /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
 558         private final int allowedModes;
 559 
 560         /** A single-bit mask representing {@code public} access,
 561          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 562          *  The value, {@code 0x01}, happens to be the same as the value of the
 563          *  {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
 564          */
 565         public static final int PUBLIC = Modifier.PUBLIC;
 566 
 567         /** A single-bit mask representing {@code private} access,
 568          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 569          *  The value, {@code 0x02}, happens to be the same as the value of the
 570          *  {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
 571          */
 572         public static final int PRIVATE = Modifier.PRIVATE;
 573 
 574         /** A single-bit mask representing {@code protected} access,
 575          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 576          *  The value, {@code 0x04}, happens to be the same as the value of the
 577          *  {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
 578          */
 579         public static final int PROTECTED = Modifier.PROTECTED;
 580 
 581         /** A single-bit mask representing {@code package} access (default access),
 582          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 583          *  The value is {@code 0x08}, which does not correspond meaningfully to
 584          *  any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
 585          */
 586         public static final int PACKAGE = Modifier.STATIC;
 587 
 588         /** A single-bit mask representing {@code module} access (default access),
 589          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 590          *  The value is {@code 0x10}, which does not correspond meaningfully to
 591          *  any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
 592          *  In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
 593          *  with this lookup mode can access all public types in the module of the
 594          *  lookup class and public types in packages exported by other modules
 595          *  to the module of the lookup class.
 596          *  @since 9
 597          */
 598         public static final int MODULE = PACKAGE << 1;
 599 
 600         private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE);
 601         private static final int TRUSTED   = -1;
 602 
 603         private static int fixmods(int mods) {
 604             mods &= (ALL_MODES - PACKAGE - MODULE);
 605             return (mods != 0) ? mods : (PACKAGE | MODULE);
 606         }
 607 
 608         /** Tells which class is performing the lookup.  It is this class against
 609          *  which checks are performed for visibility and access permissions.
 610          *  <p>
 611          *  The class implies a maximum level of access permission,
 612          *  but the permissions may be additionally limited by the bitmask
 613          *  {@link #lookupModes lookupModes}, which controls whether non-public members
 614          *  can be accessed.
 615          *  @return the lookup class, on behalf of which this lookup object finds members
 616          */
 617         public Class<?> lookupClass() {
 618             return lookupClass;
 619         }
 620 
 621         // This is just for calling out to MethodHandleImpl.
 622         private Class<?> lookupClassOrNull() {
 623             return (allowedModes == TRUSTED) ? null : lookupClass;
 624         }
 625 
 626         /** Tells which access-protection classes of members this lookup object can produce.
 627          *  The result is a bit-mask of the bits
 628          *  {@linkplain #PUBLIC PUBLIC (0x01)},
 629          *  {@linkplain #PRIVATE PRIVATE (0x02)},
 630          *  {@linkplain #PROTECTED PROTECTED (0x04)},
 631          *  {@linkplain #PACKAGE PACKAGE (0x08)},
 632          *  and {@linkplain #MODULE MODULE (0x10)}.
 633          *  <p>
 634          *  A freshly-created lookup object
 635          *  on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
 636          *  has all possible bits set, since the caller class can access all its own members,
 637          *  all public types in the caller's module, and all public types in packages exported
 638          *  by other modules to the caller's module.
 639          *  A lookup object on a new lookup class
 640          *  {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
 641          *  may have some mode bits set to zero.
 642          *  The purpose of this is to restrict access via the new lookup object,
 643          *  so that it can access only names which can be reached by the original
 644          *  lookup object, and also by the new lookup class.
 645          *  @return the lookup modes, which limit the kinds of access performed by this lookup object
 646          */
 647         public int lookupModes() {
 648             return allowedModes & ALL_MODES;
 649         }
 650 
 651         /** Embody the current class (the lookupClass) as a lookup class
 652          * for method handle creation.
 653          * Must be called by from a method in this package,
 654          * which in turn is called by a method not in this package.
 655          */
 656         Lookup(Class<?> lookupClass) {
 657             this(lookupClass, ALL_MODES);
 658             // make sure we haven't accidentally picked up a privileged class:
 659             checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
 660         }
 661 
 662         private Lookup(Class<?> lookupClass, int allowedModes) {
 663             this.lookupClass = lookupClass;
 664             this.allowedModes = allowedModes;
 665         }
 666 
 667         /**
 668          * Creates a lookup on the specified new lookup class.
 669          * The resulting object will report the specified
 670          * class as its own {@link #lookupClass lookupClass}.
 671          * <p>
 672          * However, the resulting {@code Lookup} object is guaranteed
 673          * to have no more access capabilities than the original.
 674          * In particular, access capabilities can be lost as follows:<ul>
 675          * <li>If the lookup class for this {@code Lookup} is not in a named module,
 676          * and the new lookup class is in a named module {@code M}, then no members in
 677          * {@code M}'s non-exported packages will be accessible.
 678          * <li>If the lookup for this {@code Lookup} is in a named module, and the
 679          * new lookup class is in a different module {@code M}, then no members, not even
 680          * public members in {@code M}'s exported packages, will be accessible.
 681          * <li>If the new lookup class differs from the old one,
 682          * protected members will not be accessible by virtue of inheritance.
 683          * (Protected members may continue to be accessible because of package sharing.)
 684          * <li>If the new lookup class is in a different package
 685          * than the old one, protected and default (package) members will not be accessible.
 686          * <li>If the new lookup class is not within the same package member
 687          * as the old one, private members will not be accessible.
 688          * <li>If the new lookup class is not accessible to the old lookup class,
 689          * then no members, not even public members, will be accessible.
 690          * (In all other cases, public members will continue to be accessible.)
 691          * </ul>
 692          * <p>
 693          * The resulting lookup's capabilities for loading classes
 694          * (used during {@link #findClass} invocations)
 695          * are determined by the lookup class' loader,
 696          * which may change due to this operation.
 697          *
 698          * @param requestedLookupClass the desired lookup class for the new lookup object
 699          * @return a lookup object which reports the desired lookup class
 700          * @throws NullPointerException if the argument is null
 701          */
 702         public Lookup in(Class<?> requestedLookupClass) {
 703             Objects.requireNonNull(requestedLookupClass);
 704             if (allowedModes == TRUSTED)  // IMPL_LOOKUP can make any lookup at all
 705                 return new Lookup(requestedLookupClass, ALL_MODES);
 706             if (requestedLookupClass == this.lookupClass)
 707                 return this;  // keep same capabilities
 708 
 709             int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
 710             if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
 711                 // Allowed to teleport from an unnamed to a named module but resulting
 712                 // Lookup has no access to module private members
 713                 if (this.lookupClass.getModule().isNamed()) {
 714                     newModes = 0;
 715                 } else {
 716                     newModes &= ~MODULE;
 717                 }
 718             }
 719             if ((newModes & PACKAGE) != 0
 720                 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
 721                 newModes &= ~(PACKAGE|PRIVATE);
 722             }
 723             // Allow nestmate lookups to be created without special privilege:
 724             if ((newModes & PRIVATE) != 0
 725                 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
 726                 newModes &= ~PRIVATE;
 727             }
 728             if ((newModes & PUBLIC) != 0
 729                 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
 730                 // The requested class it not accessible from the lookup class.
 731                 // No permissions.
 732                 newModes = 0;
 733             }
 734 
 735             checkUnprivilegedlookupClass(requestedLookupClass, newModes);
 736             return new Lookup(requestedLookupClass, newModes);
 737         }
 738 
 739         // Make sure outer class is initialized first.
 740         static { IMPL_NAMES.getClass(); }
 741 
 742         /** Package-private version of lookup which is trusted. */
 743         static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
 744 
 745         private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
 746             String name = lookupClass.getName();
 747             if (name.startsWith("java.lang.invoke."))
 748                 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
 749 
 750             // For caller-sensitive MethodHandles.lookup() disallow lookup from
 751             // restricted packages.  This a fragile and blunt approach.
 752             // TODO replace with a more formal and less fragile mechanism
 753             // that does not bluntly restrict classes under packages within
 754             // java.base from looking up MethodHandles or VarHandles.
 755             if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
 756                 if ((name.startsWith("java.") && !name.startsWith("java.util.concurrent.")) ||
 757                         (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
 758                     throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
 759                 }
 760             }
 761         }
 762 
 763         /**
 764          * Displays the name of the class from which lookups are to be made.
 765          * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
 766          * If there are restrictions on the access permitted to this lookup,
 767          * this is indicated by adding a suffix to the class name, consisting
 768          * of a slash and a keyword.  The keyword represents the strongest
 769          * allowed access, and is chosen as follows:
 770          * <ul>
 771          * <li>If no access is allowed, the suffix is "/noaccess".
 772          * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
 773          * <li>If only public and module access are allowed, the suffix is "/module".
 774          * <li>If only public, module and package access are allowed, the suffix is "/package".
 775          * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
 776          * </ul>
 777          * If none of the above cases apply, it is the case that full
 778          * access (public, module, package, private, and protected) is allowed.
 779          * In this case, no suffix is added.
 780          * This is true only of an object obtained originally from
 781          * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
 782          * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
 783          * always have restricted access, and will display a suffix.
 784          * <p>
 785          * (It may seem strange that protected access should be
 786          * stronger than private access.  Viewed independently from
 787          * package access, protected access is the first to be lost,
 788          * because it requires a direct subclass relationship between
 789          * caller and callee.)
 790          * @see #in
 791          */
 792         @Override
 793         public String toString() {
 794             String cname = lookupClass.getName();
 795             switch (allowedModes) {
 796             case 0:  // no privileges
 797                 return cname + "/noaccess";
 798             case PUBLIC:
 799                 return cname + "/public";
 800             case PUBLIC|MODULE:
 801                 return cname + "/module";
 802             case PUBLIC|MODULE|PACKAGE:
 803                 return cname + "/package";
 804             case ALL_MODES & ~PROTECTED:
 805                 return cname + "/private";
 806             case ALL_MODES:
 807                 return cname;
 808             case TRUSTED:
 809                 return "/trusted";  // internal only; not exported
 810             default:  // Should not happen, but it's a bitfield...
 811                 cname = cname + "/" + Integer.toHexString(allowedModes);
 812                 assert(false) : cname;
 813                 return cname;
 814             }
 815         }
 816 
 817         /**
 818          * Produces a method handle for a static method.
 819          * The type of the method handle will be that of the method.
 820          * (Since static methods do not take receivers, there is no
 821          * additional receiver argument inserted into the method handle type,
 822          * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
 823          * The method and all its argument types must be accessible to the lookup object.
 824          * <p>
 825          * The returned method handle will have
 826          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 827          * the method's variable arity modifier bit ({@code 0x0080}) is set.
 828          * <p>
 829          * If the returned method handle is invoked, the method's class will
 830          * be initialized, if it has not already been initialized.
 831          * <p><b>Example:</b>
 832          * <blockquote><pre>{@code
 833 import static java.lang.invoke.MethodHandles.*;
 834 import static java.lang.invoke.MethodType.*;
 835 ...
 836 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
 837   "asList", methodType(List.class, Object[].class));
 838 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
 839          * }</pre></blockquote>
 840          * @param refc the class from which the method is accessed
 841          * @param name the name of the method
 842          * @param type the type of the method
 843          * @return the desired method handle
 844          * @throws NoSuchMethodException if the method does not exist
 845          * @throws IllegalAccessException if access checking fails,
 846          *                                or if the method is not {@code static},
 847          *                                or if the method's variable arity modifier bit
 848          *                                is set and {@code asVarargsCollector} fails
 849          * @exception SecurityException if a security manager is present and it
 850          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
 851          * @throws NullPointerException if any argument is null
 852          */
 853         public
 854         MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
 855             MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
 856             return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
 857         }
 858 
 859         /**
 860          * Produces a method handle for a virtual method.
 861          * The type of the method handle will be that of the method,
 862          * with the receiver type (usually {@code refc}) prepended.
 863          * The method and all its argument types must be accessible to the lookup object.
 864          * <p>
 865          * When called, the handle will treat the first argument as a receiver
 866          * and dispatch on the receiver's type to determine which method
 867          * implementation to enter.
 868          * (The dispatching action is identical with that performed by an
 869          * {@code invokevirtual} or {@code invokeinterface} instruction.)
 870          * <p>
 871          * The first argument will be of type {@code refc} if the lookup
 872          * class has full privileges to access the member.  Otherwise
 873          * the member must be {@code protected} and the first argument
 874          * will be restricted in type to the lookup class.
 875          * <p>
 876          * The returned method handle will have
 877          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 878          * the method's variable arity modifier bit ({@code 0x0080}) is set.
 879          * <p>
 880          * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
 881          * instructions and method handles produced by {@code findVirtual},
 882          * if the class is {@code MethodHandle} and the name string is
 883          * {@code invokeExact} or {@code invoke}, the resulting
 884          * method handle is equivalent to one produced by
 885          * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
 886          * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
 887          * with the same {@code type} argument.
 888          * <p>
 889          * If the class is {@code VarHandle} and the name string corresponds to
 890          * the name of a signature-polymorphic access mode method, the resulting
 891          * method handle is equivalent to one produced by
 892          * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
 893          * the access mode corresponding to the name string and with the same
 894          * {@code type} arguments.
 895          * <p>
 896          * <b>Example:</b>
 897          * <blockquote><pre>{@code
 898 import static java.lang.invoke.MethodHandles.*;
 899 import static java.lang.invoke.MethodType.*;
 900 ...
 901 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
 902   "concat", methodType(String.class, String.class));
 903 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
 904   "hashCode", methodType(int.class));
 905 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
 906   "hashCode", methodType(int.class));
 907 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
 908 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
 909 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
 910 // interface method:
 911 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
 912   "subSequence", methodType(CharSequence.class, int.class, int.class));
 913 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
 914 // constructor "internal method" must be accessed differently:
 915 MethodType MT_newString = methodType(void.class); //()V for new String()
 916 try { assertEquals("impossible", lookup()
 917         .findVirtual(String.class, "<init>", MT_newString));
 918  } catch (NoSuchMethodException ex) { } // OK
 919 MethodHandle MH_newString = publicLookup()
 920   .findConstructor(String.class, MT_newString);
 921 assertEquals("", (String) MH_newString.invokeExact());
 922          * }</pre></blockquote>
 923          *
 924          * @param refc the class or interface from which the method is accessed
 925          * @param name the name of the method
 926          * @param type the type of the method, with the receiver argument omitted
 927          * @return the desired method handle
 928          * @throws NoSuchMethodException if the method does not exist
 929          * @throws IllegalAccessException if access checking fails,
 930          *                                or if the method is {@code static},
 931          *                                or if the method is {@code private} method of interface,
 932          *                                or if the method's variable arity modifier bit
 933          *                                is set and {@code asVarargsCollector} fails
 934          * @exception SecurityException if a security manager is present and it
 935          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
 936          * @throws NullPointerException if any argument is null
 937          */
 938         public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
 939             if (refc == MethodHandle.class) {
 940                 MethodHandle mh = findVirtualForMH(name, type);
 941                 if (mh != null)  return mh;
 942             } else if (refc == VarHandle.class) {
 943                 MethodHandle mh = findVirtualForVH(name, type);
 944                 if (mh != null)  return mh;
 945             }
 946             byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
 947             MemberName method = resolveOrFail(refKind, refc, name, type);
 948             return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
 949         }
 950         private MethodHandle findVirtualForMH(String name, MethodType type) {
 951             // these names require special lookups because of the implicit MethodType argument
 952             if ("invoke".equals(name))
 953                 return invoker(type);
 954             if ("invokeExact".equals(name))
 955                 return exactInvoker(type);
 956             assert(!MemberName.isMethodHandleInvokeName(name));
 957             return null;
 958         }
 959         private MethodHandle findVirtualForVH(String name, MethodType type) {
 960             try {
 961                 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
 962             } catch (IllegalArgumentException e) {
 963                 return null;
 964             }
 965         }
 966 
 967         /**
 968          * Produces a method handle which creates an object and initializes it, using
 969          * the constructor of the specified type.
 970          * The parameter types of the method handle will be those of the constructor,
 971          * while the return type will be a reference to the constructor's class.
 972          * The constructor and all its argument types must be accessible to the lookup object.
 973          * <p>
 974          * The requested type must have a return type of {@code void}.
 975          * (This is consistent with the JVM's treatment of constructor type descriptors.)
 976          * <p>
 977          * The returned method handle will have
 978          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 979          * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
 980          * <p>
 981          * If the returned method handle is invoked, the constructor's class will
 982          * be initialized, if it has not already been initialized.
 983          * <p><b>Example:</b>
 984          * <blockquote><pre>{@code
 985 import static java.lang.invoke.MethodHandles.*;
 986 import static java.lang.invoke.MethodType.*;
 987 ...
 988 MethodHandle MH_newArrayList = publicLookup().findConstructor(
 989   ArrayList.class, methodType(void.class, Collection.class));
 990 Collection orig = Arrays.asList("x", "y");
 991 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
 992 assert(orig != copy);
 993 assertEquals(orig, copy);
 994 // a variable-arity constructor:
 995 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
 996   ProcessBuilder.class, methodType(void.class, String[].class));
 997 ProcessBuilder pb = (ProcessBuilder)
 998   MH_newProcessBuilder.invoke("x", "y", "z");
 999 assertEquals("[x, y, z]", pb.command().toString());
1000          * }</pre></blockquote>
1001          * @param refc the class or interface from which the method is accessed
1002          * @param type the type of the method, with the receiver argument omitted, and a void return type
1003          * @return the desired method handle
1004          * @throws NoSuchMethodException if the constructor does not exist
1005          * @throws IllegalAccessException if access checking fails
1006          *                                or if the method's variable arity modifier bit
1007          *                                is set and {@code asVarargsCollector} fails
1008          * @exception SecurityException if a security manager is present and it
1009          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1010          * @throws NullPointerException if any argument is null
1011          */
1012         public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1013             if (refc.isArray()) {
1014                 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1015             }
1016             String name = "<init>";
1017             MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1018             return getDirectConstructor(refc, ctor);
1019         }
1020 
1021         /**
1022          * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1023          * initializer of the class is not run.
1024          * <p>
1025          * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1026          * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1027          * load the requested class, and then determines whether the class is accessible to this lookup object.
1028          *
1029          * @param targetName the fully qualified name of the class to be looked up.
1030          * @return the requested class.
1031          * @exception SecurityException if a security manager is present and it
1032          *            <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1033          * @throws LinkageError if the linkage fails
1034          * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1035          * @throws IllegalAccessException if the class is not accessible, using the allowed access
1036          * modes.
1037          * @exception SecurityException if a security manager is present and it
1038          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1039          * @since 9
1040          */
1041         public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1042             Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1043             return accessClass(targetClass);
1044         }
1045 
1046         /**
1047          * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1048          * static initializer of the class is not run.
1049          * <p>
1050          * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1051          * {@linkplain #lookupModes() lookup modes}.
1052          *
1053          * @param targetClass the class to be access-checked
1054          *
1055          * @return the class that has been access-checked
1056          *
1057          * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1058          * modes.
1059          * @exception SecurityException if a security manager is present and it
1060          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1061          * @since 9
1062          */
1063         public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1064             if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1065                 throw new MemberName(targetClass).makeAccessException("access violation", this);
1066             }
1067             checkSecurityManager(targetClass, null);
1068             return targetClass;
1069         }
1070 
1071         /**
1072          * Produces an early-bound method handle for a virtual method.
1073          * It will bypass checks for overriding methods on the receiver,
1074          * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1075          * instruction from within the explicitly specified {@code specialCaller}.
1076          * The type of the method handle will be that of the method,
1077          * with a suitably restricted receiver type prepended.
1078          * (The receiver type will be {@code specialCaller} or a subtype.)
1079          * The method and all its argument types must be accessible
1080          * to the lookup object.
1081          * <p>
1082          * Before method resolution,
1083          * if the explicitly specified caller class is not identical with the
1084          * lookup class, or if this lookup object does not have
1085          * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1086          * privileges, the access fails.
1087          * <p>
1088          * The returned method handle will have
1089          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1090          * the method's variable arity modifier bit ({@code 0x0080}) is set.
1091          * <p style="font-size:smaller;">
1092          * <em>(Note:  JVM internal methods named {@code "<init>"} are not visible to this API,
1093          * even though the {@code invokespecial} instruction can refer to them
1094          * in special circumstances.  Use {@link #findConstructor findConstructor}
1095          * to access instance initialization methods in a safe manner.)</em>
1096          * <p><b>Example:</b>
1097          * <blockquote><pre>{@code
1098 import static java.lang.invoke.MethodHandles.*;
1099 import static java.lang.invoke.MethodType.*;
1100 ...
1101 static class Listie extends ArrayList {
1102   public String toString() { return "[wee Listie]"; }
1103   static Lookup lookup() { return MethodHandles.lookup(); }
1104 }
1105 ...
1106 // no access to constructor via invokeSpecial:
1107 MethodHandle MH_newListie = Listie.lookup()
1108   .findConstructor(Listie.class, methodType(void.class));
1109 Listie l = (Listie) MH_newListie.invokeExact();
1110 try { assertEquals("impossible", Listie.lookup().findSpecial(
1111         Listie.class, "<init>", methodType(void.class), Listie.class));
1112  } catch (NoSuchMethodException ex) { } // OK
1113 // access to super and self methods via invokeSpecial:
1114 MethodHandle MH_super = Listie.lookup().findSpecial(
1115   ArrayList.class, "toString" , methodType(String.class), Listie.class);
1116 MethodHandle MH_this = Listie.lookup().findSpecial(
1117   Listie.class, "toString" , methodType(String.class), Listie.class);
1118 MethodHandle MH_duper = Listie.lookup().findSpecial(
1119   Object.class, "toString" , methodType(String.class), Listie.class);
1120 assertEquals("[]", (String) MH_super.invokeExact(l));
1121 assertEquals(""+l, (String) MH_this.invokeExact(l));
1122 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1123 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1124         String.class, "toString", methodType(String.class), Listie.class));
1125  } catch (IllegalAccessException ex) { } // OK
1126 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1127 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1128          * }</pre></blockquote>
1129          *
1130          * @param refc the class or interface from which the method is accessed
1131          * @param name the name of the method (which must not be "&lt;init&gt;")
1132          * @param type the type of the method, with the receiver argument omitted
1133          * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1134          * @return the desired method handle
1135          * @throws NoSuchMethodException if the method does not exist
1136          * @throws IllegalAccessException if access checking fails,
1137          *                                or if the method is {@code static},
1138          *                                or if the method's variable arity modifier bit
1139          *                                is set and {@code asVarargsCollector} fails
1140          * @exception SecurityException if a security manager is present and it
1141          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1142          * @throws NullPointerException if any argument is null
1143          */
1144         public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1145                                         Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1146             checkSpecialCaller(specialCaller, refc);
1147             Lookup specialLookup = this.in(specialCaller);
1148             MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1149             return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1150         }
1151 
1152         /**
1153          * Produces a method handle giving read access to a non-static field.
1154          * The type of the method handle will have a return type of the field's
1155          * value type.
1156          * The method handle's single argument will be the instance containing
1157          * the field.
1158          * Access checking is performed immediately on behalf of the lookup class.
1159          * @param refc the class or interface from which the method is accessed
1160          * @param name the field's name
1161          * @param type the field's type
1162          * @return a method handle which can load values from the field
1163          * @throws NoSuchFieldException if the field does not exist
1164          * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1165          * @exception SecurityException if a security manager is present and it
1166          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1167          * @throws NullPointerException if any argument is null
1168          * @see #findVarHandle(Class, String, Class)
1169          */
1170         public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1171             MemberName field = resolveOrFail(REF_getField, refc, name, type);
1172             return getDirectField(REF_getField, refc, field);
1173         }
1174 
1175         /**
1176          * Produces a method handle giving write access to a non-static field.
1177          * The type of the method handle will have a void return type.
1178          * The method handle will take two arguments, the instance containing
1179          * the field, and the value to be stored.
1180          * The second argument will be of the field's value type.
1181          * Access checking is performed immediately on behalf of the lookup class.
1182          * @param refc the class or interface from which the method is accessed
1183          * @param name the field's name
1184          * @param type the field's type
1185          * @return a method handle which can store values into the field
1186          * @throws NoSuchFieldException if the field does not exist
1187          * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1188          * @exception SecurityException if a security manager is present and it
1189          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1190          * @throws NullPointerException if any argument is null
1191          * @see #findVarHandle(Class, String, Class)
1192          */
1193         public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1194             MemberName field = resolveOrFail(REF_putField, refc, name, type);
1195             return getDirectField(REF_putField, refc, field);
1196         }
1197 
1198         /**
1199          * Produces a VarHandle giving access to non-static fields of type
1200          * {@code T} declared by a receiver class of type {@code R}, supporting
1201          * shape {@code (R : T)}.
1202          * <p>
1203          * Access checking is performed immediately on behalf of the lookup
1204          * class.
1205          * <p>
1206          * Certain access modes of the returned VarHandle are unsupported under
1207          * the following conditions:
1208          * <ul>
1209          * <li>if the field is declared {@code final}, then the write, atomic
1210          *     update, numeric atomic update, and bitwise atomic update access
1211          *     modes are unsupported.
1212          * <li>if the field type is anything other than {@code byte},
1213          *     {@code short}, {@code char}, {@code int}, {@code long},
1214          *     {@code float}, or {@code double} then numeric atomic update
1215          *     access modes are unsupported.
1216          * <li>if the field type is anything other than {@code boolean},
1217          *     {@code byte}, {@code short}, {@code char}, {@code int} or
1218          *     {@code long} then bitwise atomic update access modes are
1219          *     unsupported.
1220          * </ul>
1221          * <p>
1222          * If the field is declared {@code volatile} then the returned VarHandle
1223          * will override access to the field (effectively ignore the
1224          * {@code volatile} declaration) in accordance to it's specified
1225          * access modes.
1226          * <p>
1227          * If the field type is {@code float} or {@code double} then numeric
1228          * and atomic update access modes compare values using their bitwise
1229          * representation (see {@link Float#floatToRawIntBits} and
1230          * {@link Double#doubleToRawLongBits}, respectively).
1231          * @apiNote
1232          * Bitwise comparison of {@code float} values or {@code double} values,
1233          * as performed by the numeric and atomic update access modes, differ
1234          * from the primitive {@code ==} operator and the {@link Float#equals}
1235          * and {@link Double#equals} methods, specifically with respect to
1236          * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1237          * Care should be taken when performing a compare and set or a compare
1238          * and exchange operation with such values since the operation may
1239          * unexpectedly fail.
1240          * There are many possible NaN values that are considered to be
1241          * {@code NaN} in Java, although no IEEE 754 floating-point operation
1242          * provided by Java can distinguish between them.  Operation failure can
1243          * occur if the expected or witness value is a NaN value and it is
1244          * transformed (perhaps in a platform specific manner) into another NaN
1245          * value, and thus has a different bitwise representation (see
1246          * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1247          * details).
1248          * The values {@code -0.0} and {@code +0.0} have different bitwise
1249          * representations but are considered equal when using the primitive
1250          * {@code ==} operator.  Operation failure can occur if, for example, a
1251          * numeric algorithm computes an expected value to be say {@code -0.0}
1252          * and previously computed the witness value to be say {@code +0.0}.
1253          * @param recv the receiver class, of type {@code R}, that declares the
1254          * non-static field
1255          * @param name the field's name
1256          * @param type the field's type, of type {@code T}
1257          * @return a VarHandle giving access to non-static fields.
1258          * @throws NoSuchFieldException if the field does not exist
1259          * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1260          * @exception SecurityException if a security manager is present and it
1261          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1262          * @throws NullPointerException if any argument is null
1263          * @since 9
1264          */
1265         public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1266             MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1267             MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1268             return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1269         }
1270 
1271         /**
1272          * Produces a method handle giving read access to a static field.
1273          * The type of the method handle will have a return type of the field's
1274          * value type.
1275          * The method handle will take no arguments.
1276          * Access checking is performed immediately on behalf of the lookup class.
1277          * <p>
1278          * If the returned method handle is invoked, the field's class will
1279          * be initialized, if it has not already been initialized.
1280          * @param refc the class or interface from which the method is accessed
1281          * @param name the field's name
1282          * @param type the field's type
1283          * @return a method handle which can load values from the field
1284          * @throws NoSuchFieldException if the field does not exist
1285          * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1286          * @exception SecurityException if a security manager is present and it
1287          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1288          * @throws NullPointerException if any argument is null
1289          */
1290         public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1291             MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1292             return getDirectField(REF_getStatic, refc, field);
1293         }
1294 
1295         /**
1296          * Produces a method handle giving write access to a static field.
1297          * The type of the method handle will have a void return type.
1298          * The method handle will take a single
1299          * argument, of the field's value type, the value to be stored.
1300          * Access checking is performed immediately on behalf of the lookup class.
1301          * <p>
1302          * If the returned method handle is invoked, the field's class will
1303          * be initialized, if it has not already been initialized.
1304          * @param refc the class or interface from which the method is accessed
1305          * @param name the field's name
1306          * @param type the field's type
1307          * @return a method handle which can store values into the field
1308          * @throws NoSuchFieldException if the field does not exist
1309          * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1310          * @exception SecurityException if a security manager is present and it
1311          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1312          * @throws NullPointerException if any argument is null
1313          */
1314         public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1315             MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1316             return getDirectField(REF_putStatic, refc, field);
1317         }
1318 
1319         /**
1320          * Produces a VarHandle giving access to a static field of type
1321          * {@code T} declared by a given declaring class, supporting shape
1322          * {@code ((empty) : T)}.
1323          * <p>
1324          * Access checking is performed immediately on behalf of the lookup
1325          * class.
1326          * <p>
1327          * If the returned VarHandle is operated on, the declaring class will be
1328          * initialized, if it has not already been initialized.
1329          * <p>
1330          * Certain access modes of the returned VarHandle are unsupported under
1331          * the following conditions:
1332          * <ul>
1333          * <li>if the field is declared {@code final}, then the write, atomic
1334          *     update, numeric atomic update, and bitwise atomic update access
1335          *     modes are unsupported.
1336          * <li>if the field type is anything other than {@code byte},
1337          *     {@code short}, {@code char}, {@code int}, {@code long},
1338          *     {@code float}, or {@code double}, then numeric atomic update
1339          *     access modes are unsupported.
1340          * <li>if the field type is anything other than {@code boolean},
1341          *     {@code byte}, {@code short}, {@code char}, {@code int} or
1342          *     {@code long} then bitwise atomic update access modes are
1343          *     unsupported.
1344          * </ul>
1345          * <p>
1346          * If the field is declared {@code volatile} then the returned VarHandle
1347          * will override access to the field (effectively ignore the
1348          * {@code volatile} declaration) in accordance to it's specified
1349          * access modes.
1350          * <p>
1351          * If the field type is {@code float} or {@code double} then numeric
1352          * and atomic update access modes compare values using their bitwise
1353          * representation (see {@link Float#floatToRawIntBits} and
1354          * {@link Double#doubleToRawLongBits}, respectively).
1355          * @apiNote
1356          * Bitwise comparison of {@code float} values or {@code double} values,
1357          * as performed by the numeric and atomic update access modes, differ
1358          * from the primitive {@code ==} operator and the {@link Float#equals}
1359          * and {@link Double#equals} methods, specifically with respect to
1360          * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1361          * Care should be taken when performing a compare and set or a compare
1362          * and exchange operation with such values since the operation may
1363          * unexpectedly fail.
1364          * There are many possible NaN values that are considered to be
1365          * {@code NaN} in Java, although no IEEE 754 floating-point operation
1366          * provided by Java can distinguish between them.  Operation failure can
1367          * occur if the expected or witness value is a NaN value and it is
1368          * transformed (perhaps in a platform specific manner) into another NaN
1369          * value, and thus has a different bitwise representation (see
1370          * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1371          * details).
1372          * The values {@code -0.0} and {@code +0.0} have different bitwise
1373          * representations but are considered equal when using the primitive
1374          * {@code ==} operator.  Operation failure can occur if, for example, a
1375          * numeric algorithm computes an expected value to be say {@code -0.0}
1376          * and previously computed the witness value to be say {@code +0.0}.
1377          * @param decl the class that declares the static field
1378          * @param name the field's name
1379          * @param type the field's type, of type {@code T}
1380          * @return a VarHandle giving access to a static field
1381          * @throws NoSuchFieldException if the field does not exist
1382          * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1383          * @exception SecurityException if a security manager is present and it
1384          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1385          * @throws NullPointerException if any argument is null
1386          * @since 9
1387          */
1388         public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1389             MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1390             MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1391             return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1392         }
1393 
1394         /**
1395          * Produces an early-bound method handle for a non-static method.
1396          * The receiver must have a supertype {@code defc} in which a method
1397          * of the given name and type is accessible to the lookup class.
1398          * The method and all its argument types must be accessible to the lookup object.
1399          * The type of the method handle will be that of the method,
1400          * without any insertion of an additional receiver parameter.
1401          * The given receiver will be bound into the method handle,
1402          * so that every call to the method handle will invoke the
1403          * requested method on the given receiver.
1404          * <p>
1405          * The returned method handle will have
1406          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1407          * the method's variable arity modifier bit ({@code 0x0080}) is set
1408          * <em>and</em> the trailing array argument is not the only argument.
1409          * (If the trailing array argument is the only argument,
1410          * the given receiver value will be bound to it.)
1411          * <p>
1412          * This is equivalent to the following code:
1413          * <blockquote><pre>{@code
1414 import static java.lang.invoke.MethodHandles.*;
1415 import static java.lang.invoke.MethodType.*;
1416 ...
1417 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1418 MethodHandle mh1 = mh0.bindTo(receiver);
1419 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1420 return mh1;
1421          * }</pre></blockquote>
1422          * where {@code defc} is either {@code receiver.getClass()} or a super
1423          * type of that class, in which the requested method is accessible
1424          * to the lookup class.
1425          * (Note that {@code bindTo} does not preserve variable arity.)
1426          * @param receiver the object from which the method is accessed
1427          * @param name the name of the method
1428          * @param type the type of the method, with the receiver argument omitted
1429          * @return the desired method handle
1430          * @throws NoSuchMethodException if the method does not exist
1431          * @throws IllegalAccessException if access checking fails
1432          *                                or if the method's variable arity modifier bit
1433          *                                is set and {@code asVarargsCollector} fails
1434          * @exception SecurityException if a security manager is present and it
1435          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1436          * @throws NullPointerException if any argument is null
1437          * @see MethodHandle#bindTo
1438          * @see #findVirtual
1439          */
1440         public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1441             Class<? extends Object> refc = receiver.getClass(); // may get NPE
1442             MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1443             MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1444             return mh.bindArgumentL(0, receiver).setVarargs(method);
1445         }
1446 
1447         /**
1448          * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1449          * to <i>m</i>, if the lookup class has permission.
1450          * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1451          * If <i>m</i> is virtual, overriding is respected on every call.
1452          * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1453          * The type of the method handle will be that of the method,
1454          * with the receiver type prepended (but only if it is non-static).
1455          * If the method's {@code accessible} flag is not set,
1456          * access checking is performed immediately on behalf of the lookup class.
1457          * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1458          * <p>
1459          * The returned method handle will have
1460          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1461          * the method's variable arity modifier bit ({@code 0x0080}) is set.
1462          * <p>
1463          * If <i>m</i> is static, and
1464          * if the returned method handle is invoked, the method's class will
1465          * be initialized, if it has not already been initialized.
1466          * @param m the reflected method
1467          * @return a method handle which can invoke the reflected method
1468          * @throws IllegalAccessException if access checking fails
1469          *                                or if the method's variable arity modifier bit
1470          *                                is set and {@code asVarargsCollector} fails
1471          * @throws NullPointerException if the argument is null
1472          */
1473         public MethodHandle unreflect(Method m) throws IllegalAccessException {
1474             if (m.getDeclaringClass() == MethodHandle.class) {
1475                 MethodHandle mh = unreflectForMH(m);
1476                 if (mh != null)  return mh;
1477             }
1478             if (m.getDeclaringClass() == VarHandle.class) {
1479                 MethodHandle mh = unreflectForVH(m);
1480                 if (mh != null)  return mh;
1481             }
1482             MemberName method = new MemberName(m);
1483             byte refKind = method.getReferenceKind();
1484             if (refKind == REF_invokeSpecial)
1485                 refKind = REF_invokeVirtual;
1486             assert(method.isMethod());
1487             Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1488             return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1489         }
1490         private MethodHandle unreflectForMH(Method m) {
1491             // these names require special lookups because they throw UnsupportedOperationException
1492             if (MemberName.isMethodHandleInvokeName(m.getName()))
1493                 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1494             return null;
1495         }
1496         private MethodHandle unreflectForVH(Method m) {
1497             // these names require special lookups because they throw UnsupportedOperationException
1498             if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1499                 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1500             return null;
1501         }
1502 
1503         /**
1504          * Produces a method handle for a reflected method.
1505          * It will bypass checks for overriding methods on the receiver,
1506          * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1507          * instruction from within the explicitly specified {@code specialCaller}.
1508          * The type of the method handle will be that of the method,
1509          * with a suitably restricted receiver type prepended.
1510          * (The receiver type will be {@code specialCaller} or a subtype.)
1511          * If the method's {@code accessible} flag is not set,
1512          * access checking is performed immediately on behalf of the lookup class,
1513          * as if {@code invokespecial} instruction were being linked.
1514          * <p>
1515          * Before method resolution,
1516          * if the explicitly specified caller class is not identical with the
1517          * lookup class, or if this lookup object does not have
1518          * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1519          * privileges, the access fails.
1520          * <p>
1521          * The returned method handle will have
1522          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1523          * the method's variable arity modifier bit ({@code 0x0080}) is set.
1524          * @param m the reflected method
1525          * @param specialCaller the class nominally calling the method
1526          * @return a method handle which can invoke the reflected method
1527          * @throws IllegalAccessException if access checking fails,
1528          *                                or if the method is {@code static},
1529          *                                or if the method's variable arity modifier bit
1530          *                                is set and {@code asVarargsCollector} fails
1531          * @throws NullPointerException if any argument is null
1532          */
1533         public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1534             checkSpecialCaller(specialCaller, null);
1535             Lookup specialLookup = this.in(specialCaller);
1536             MemberName method = new MemberName(m, true);
1537             assert(method.isMethod());
1538             // ignore m.isAccessible:  this is a new kind of access
1539             return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1540         }
1541 
1542         /**
1543          * Produces a method handle for a reflected constructor.
1544          * The type of the method handle will be that of the constructor,
1545          * with the return type changed to the declaring class.
1546          * The method handle will perform a {@code newInstance} operation,
1547          * creating a new instance of the constructor's class on the
1548          * arguments passed to the method handle.
1549          * <p>
1550          * If the constructor's {@code accessible} flag is not set,
1551          * access checking is performed immediately on behalf of the lookup class.
1552          * <p>
1553          * The returned method handle will have
1554          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1555          * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1556          * <p>
1557          * If the returned method handle is invoked, the constructor's class will
1558          * be initialized, if it has not already been initialized.
1559          * @param c the reflected constructor
1560          * @return a method handle which can invoke the reflected constructor
1561          * @throws IllegalAccessException if access checking fails
1562          *                                or if the method's variable arity modifier bit
1563          *                                is set and {@code asVarargsCollector} fails
1564          * @throws NullPointerException if the argument is null
1565          */
1566         public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1567             MemberName ctor = new MemberName(c);
1568             assert(ctor.isConstructor());
1569             Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1570             return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1571         }
1572 
1573         /**
1574          * Produces a method handle giving read access to a reflected field.
1575          * The type of the method handle will have a return type of the field's
1576          * value type.
1577          * If the field is static, the method handle will take no arguments.
1578          * Otherwise, its single argument will be the instance containing
1579          * the field.
1580          * If the field's {@code accessible} flag is not set,
1581          * access checking is performed immediately on behalf of the lookup class.
1582          * <p>
1583          * If the field is static, and
1584          * if the returned method handle is invoked, the field's class will
1585          * be initialized, if it has not already been initialized.
1586          * @param f the reflected field
1587          * @return a method handle which can load values from the reflected field
1588          * @throws IllegalAccessException if access checking fails
1589          * @throws NullPointerException if the argument is null
1590          */
1591         public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1592             return unreflectField(f, false);
1593         }
1594         private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1595             MemberName field = new MemberName(f, isSetter);
1596             assert(isSetter
1597                     ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1598                     : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1599             Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1600             return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1601         }
1602 
1603         /**
1604          * Produces a method handle giving write access to a reflected field.
1605          * The type of the method handle will have a void return type.
1606          * If the field is static, the method handle will take a single
1607          * argument, of the field's value type, the value to be stored.
1608          * Otherwise, the two arguments will be the instance containing
1609          * the field, and the value to be stored.
1610          * If the field's {@code accessible} flag is not set,
1611          * access checking is performed immediately on behalf of the lookup class.
1612          * <p>
1613          * If the field is static, and
1614          * if the returned method handle is invoked, the field's class will
1615          * be initialized, if it has not already been initialized.
1616          * @param f the reflected field
1617          * @return a method handle which can store values into the reflected field
1618          * @throws IllegalAccessException if access checking fails
1619          * @throws NullPointerException if the argument is null
1620          */
1621         public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1622             return unreflectField(f, true);
1623         }
1624 
1625         /**
1626          * Produces a VarHandle that accesses fields of type {@code T} declared
1627          * by a class of type {@code R}, as described by the given reflected
1628          * field.
1629          * If the field is non-static the VarHandle supports a shape of
1630          * {@code (R : T)}, otherwise supports a shape of {@code ((empty) : T)}.
1631          * <p>
1632          * Access checking is performed immediately on behalf of the lookup
1633          * class, regardless of the value of the field's {@code accessible}
1634          * flag.
1635          * <p>
1636          * If the field is static, and if the returned VarHandle is operated
1637          * on, the field's declaring class will be initialized, if it has not
1638          * already been initialized.
1639          * <p>
1640          * Certain access modes of the returned VarHandle are unsupported under
1641          * the following conditions:
1642          * <ul>
1643          * <li>if the field is declared {@code final}, then the write, atomic
1644          *     update, numeric atomic update, and bitwise atomic update access
1645          *     modes are unsupported.
1646          * <li>if the field type is anything other than {@code byte},
1647          *     {@code short}, {@code char}, {@code int}, {@code long},
1648          *     {@code float}, or {@code double} then numeric atomic update
1649          *     access modes are unsupported.
1650          * <li>if the field type is anything other than {@code boolean},
1651          *     {@code byte}, {@code short}, {@code char}, {@code int} or
1652          *     {@code long} then bitwise atomic update access modes are
1653          *     unsupported.
1654          * </ul>
1655          * <p>
1656          * If the field is declared {@code volatile} then the returned VarHandle
1657          * will override access to the field (effectively ignore the
1658          * {@code volatile} declaration) in accordance to it's specified
1659          * access modes.
1660          * <p>
1661          * If the field type is {@code float} or {@code double} then numeric
1662          * and atomic update access modes compare values using their bitwise
1663          * representation (see {@link Float#floatToRawIntBits} and
1664          * {@link Double#doubleToRawLongBits}, respectively).
1665          * @apiNote
1666          * Bitwise comparison of {@code float} values or {@code double} values,
1667          * as performed by the numeric and atomic update access modes, differ
1668          * from the primitive {@code ==} operator and the {@link Float#equals}
1669          * and {@link Double#equals} methods, specifically with respect to
1670          * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1671          * Care should be taken when performing a compare and set or a compare
1672          * and exchange operation with such values since the operation may
1673          * unexpectedly fail.
1674          * There are many possible NaN values that are considered to be
1675          * {@code NaN} in Java, although no IEEE 754 floating-point operation
1676          * provided by Java can distinguish between them.  Operation failure can
1677          * occur if the expected or witness value is a NaN value and it is
1678          * transformed (perhaps in a platform specific manner) into another NaN
1679          * value, and thus has a different bitwise representation (see
1680          * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1681          * details).
1682          * The values {@code -0.0} and {@code +0.0} have different bitwise
1683          * representations but are considered equal when using the primitive
1684          * {@code ==} operator.  Operation failure can occur if, for example, a
1685          * numeric algorithm computes an expected value to be say {@code -0.0}
1686          * and previously computed the witness value to be say {@code +0.0}.
1687          * @param f the reflected field, with a field of type {@code T}, and
1688          * a declaring class of type {@code R}
1689          * @return a VarHandle giving access to non-static fields or a static
1690          * field
1691          * @throws IllegalAccessException if access checking fails
1692          * @throws NullPointerException if the argument is null
1693          * @since 9
1694          */
1695         public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1696             MemberName getField = new MemberName(f, false);
1697             MemberName putField = new MemberName(f, true);
1698             return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1699                                                       f.getDeclaringClass(), getField, putField);
1700         }
1701 
1702         /**
1703          * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1704          * created by this lookup object or a similar one.
1705          * Security and access checks are performed to ensure that this lookup object
1706          * is capable of reproducing the target method handle.
1707          * This means that the cracking may fail if target is a direct method handle
1708          * but was created by an unrelated lookup object.
1709          * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1710          * and was created by a lookup object for a different class.
1711          * @param target a direct method handle to crack into symbolic reference components
1712          * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1713          * @exception SecurityException if a security manager is present and it
1714          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1715          * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1716          * @exception NullPointerException if the target is {@code null}
1717          * @see MethodHandleInfo
1718          * @since 1.8
1719          */
1720         public MethodHandleInfo revealDirect(MethodHandle target) {
1721             MemberName member = target.internalMemberName();
1722             if (member == null || (!member.isResolved() &&
1723                                    !member.isMethodHandleInvoke() &&
1724                                    !member.isVarHandleMethodInvoke()))
1725                 throw newIllegalArgumentException("not a direct method handle");
1726             Class<?> defc = member.getDeclaringClass();
1727             byte refKind = member.getReferenceKind();
1728             assert(MethodHandleNatives.refKindIsValid(refKind));
1729             if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1730                 // Devirtualized method invocation is usually formally virtual.
1731                 // To avoid creating extra MemberName objects for this common case,
1732                 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1733                 refKind = REF_invokeVirtual;
1734             if (refKind == REF_invokeVirtual && defc.isInterface())
1735                 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1736                 refKind = REF_invokeInterface;
1737             // Check SM permissions and member access before cracking.
1738             try {
1739                 checkAccess(refKind, defc, member);
1740                 checkSecurityManager(defc, member);
1741             } catch (IllegalAccessException ex) {
1742                 throw new IllegalArgumentException(ex);
1743             }
1744             if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1745                 Class<?> callerClass = target.internalCallerClass();
1746                 if (!hasPrivateAccess() || callerClass != lookupClass())
1747                     throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1748             }
1749             // Produce the handle to the results.
1750             return new InfoFromMemberName(this, member, refKind);
1751         }
1752 
1753         /// Helper methods, all package-private.
1754 
1755         MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1756             checkSymbolicClass(refc);  // do this before attempting to resolve
1757             Objects.requireNonNull(name);
1758             Objects.requireNonNull(type);
1759             return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1760                                             NoSuchFieldException.class);
1761         }
1762 
1763         MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1764             checkSymbolicClass(refc);  // do this before attempting to resolve
1765             Objects.requireNonNull(name);
1766             Objects.requireNonNull(type);
1767             checkMethodName(refKind, name);  // NPE check on name
1768             return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1769                                             NoSuchMethodException.class);
1770         }
1771 
1772         MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1773             checkSymbolicClass(member.getDeclaringClass());  // do this before attempting to resolve
1774             Objects.requireNonNull(member.getName());
1775             Objects.requireNonNull(member.getType());
1776             return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1777                                             ReflectiveOperationException.class);
1778         }
1779 
1780         void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1781             Objects.requireNonNull(refc);
1782             Class<?> caller = lookupClassOrNull();
1783             if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1784                 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
1785         }
1786 
1787         /** Check name for an illegal leading "&lt;" character. */
1788         void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1789             if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1790                 throw new NoSuchMethodException("illegal method name: "+name);
1791         }
1792 
1793 
1794         /**
1795          * Find my trustable caller class if m is a caller sensitive method.
1796          * If this lookup object has private access, then the caller class is the lookupClass.
1797          * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1798          */
1799         Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1800             Class<?> callerClass = null;
1801             if (MethodHandleNatives.isCallerSensitive(m)) {
1802                 // Only lookups with private access are allowed to resolve caller-sensitive methods
1803                 if (hasPrivateAccess()) {
1804                     callerClass = lookupClass;
1805                 } else {
1806                     throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1807                 }
1808             }
1809             return callerClass;
1810         }
1811 
1812         private boolean hasPrivateAccess() {
1813             return (allowedModes & PRIVATE) != 0;
1814         }
1815 
1816         /**
1817          * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1818          * Determines a trustable caller class to compare with refc, the symbolic reference class.
1819          * If this lookup object has private access, then the caller class is the lookupClass.
1820          */
1821         void checkSecurityManager(Class<?> refc, MemberName m) {
1822             SecurityManager smgr = System.getSecurityManager();
1823             if (smgr == null)  return;
1824             if (allowedModes == TRUSTED)  return;
1825 
1826             // Step 1:
1827             boolean fullPowerLookup = hasPrivateAccess();
1828             if (!fullPowerLookup ||
1829                 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1830                 ReflectUtil.checkPackageAccess(refc);
1831             }
1832 
1833             if (m == null) {  // findClass or accessClass
1834                 // Step 2b:
1835                 if (!fullPowerLookup) {
1836                     smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1837                 }
1838                 return;
1839             }
1840 
1841             // Step 2a:
1842             if (m.isPublic()) return;
1843             if (!fullPowerLookup) {
1844                 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1845             }
1846 
1847             // Step 3:
1848             Class<?> defc = m.getDeclaringClass();
1849             if (!fullPowerLookup && defc != refc) {
1850                 ReflectUtil.checkPackageAccess(defc);
1851             }
1852         }
1853 
1854         void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1855             boolean wantStatic = (refKind == REF_invokeStatic);
1856             String message;
1857             if (m.isConstructor())
1858                 message = "expected a method, not a constructor";
1859             else if (!m.isMethod())
1860                 message = "expected a method";
1861             else if (wantStatic != m.isStatic())
1862                 message = wantStatic ? "expected a static method" : "expected a non-static method";
1863             else
1864                 { checkAccess(refKind, refc, m); return; }
1865             throw m.makeAccessException(message, this);
1866         }
1867 
1868         void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1869             boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1870             String message;
1871             if (wantStatic != m.isStatic())
1872                 message = wantStatic ? "expected a static field" : "expected a non-static field";
1873             else
1874                 { checkAccess(refKind, refc, m); return; }
1875             throw m.makeAccessException(message, this);
1876         }
1877 
1878         /** Check public/protected/private bits on the symbolic reference class and its member. */
1879         void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1880             assert(m.referenceKindIsConsistentWith(refKind) &&
1881                    MethodHandleNatives.refKindIsValid(refKind) &&
1882                    (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1883             int allowedModes = this.allowedModes;
1884             if (allowedModes == TRUSTED)  return;
1885             int mods = m.getModifiers();
1886             if (Modifier.isProtected(mods) &&
1887                     refKind == REF_invokeVirtual &&
1888                     m.getDeclaringClass() == Object.class &&
1889                     m.getName().equals("clone") &&
1890                     refc.isArray()) {
1891                 // The JVM does this hack also.
1892                 // (See ClassVerifier::verify_invoke_instructions
1893                 // and LinkResolver::check_method_accessability.)
1894                 // Because the JVM does not allow separate methods on array types,
1895                 // there is no separate method for int[].clone.
1896                 // All arrays simply inherit Object.clone.
1897                 // But for access checking logic, we make Object.clone
1898                 // (normally protected) appear to be public.
1899                 // Later on, when the DirectMethodHandle is created,
1900                 // its leading argument will be restricted to the
1901                 // requested array type.
1902                 // N.B. The return type is not adjusted, because
1903                 // that is *not* the bytecode behavior.
1904                 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1905             }
1906             if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1907                 // cannot "new" a protected ctor in a different package
1908                 mods ^= Modifier.PROTECTED;
1909             }
1910             if (Modifier.isFinal(mods) &&
1911                     MethodHandleNatives.refKindIsSetter(refKind))
1912                 throw m.makeAccessException("unexpected set of a final field", this);
1913             int requestedModes = fixmods(mods);  // adjust 0 => PACKAGE
1914             if ((requestedModes & allowedModes) != 0) {
1915                 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1916                                                     mods, lookupClass(), allowedModes))
1917                     return;
1918             } else {
1919                 // Protected members can also be checked as if they were package-private.
1920                 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1921                         && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1922                     return;
1923             }
1924             throw m.makeAccessException(accessFailedMessage(refc, m), this);
1925         }
1926 
1927         String accessFailedMessage(Class<?> refc, MemberName m) {
1928             Class<?> defc = m.getDeclaringClass();
1929             int mods = m.getModifiers();
1930             // check the class first:
1931             boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1932                                (defc == refc ||
1933                                 Modifier.isPublic(refc.getModifiers())));
1934             if (!classOK && (allowedModes & PACKAGE) != 0) {
1935                 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1936                            (defc == refc ||
1937                             VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1938             }
1939             if (!classOK)
1940                 return "class is not public";
1941             if (Modifier.isPublic(mods))
1942                 return "access to public member failed";  // (how?, module not readable?)
1943             if (Modifier.isPrivate(mods))
1944                 return "member is private";
1945             if (Modifier.isProtected(mods))
1946                 return "member is protected";
1947             return "member is private to package";
1948         }
1949 
1950         private static final boolean ALLOW_NESTMATE_ACCESS = false;
1951 
1952         private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
1953             int allowedModes = this.allowedModes;
1954             if (allowedModes == TRUSTED)  return;
1955             if (!hasPrivateAccess()
1956                 || (specialCaller != lookupClass()
1957                        // ensure non-abstract methods in superinterfaces can be special-invoked
1958                     && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
1959                     && !(ALLOW_NESTMATE_ACCESS &&
1960                          VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1961                 throw new MemberName(specialCaller).
1962                     makeAccessException("no private access for invokespecial", this);
1963         }
1964 
1965         private boolean restrictProtectedReceiver(MemberName method) {
1966             // The accessing class only has the right to use a protected member
1967             // on itself or a subclass.  Enforce that restriction, from JVMS 5.4.4, etc.
1968             if (!method.isProtected() || method.isStatic()
1969                 || allowedModes == TRUSTED
1970                 || method.getDeclaringClass() == lookupClass()
1971                 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1972                 || (ALLOW_NESTMATE_ACCESS &&
1973                     VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1974                 return false;
1975             return true;
1976         }
1977         private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
1978             assert(!method.isStatic());
1979             // receiver type of mh is too wide; narrow to caller
1980             if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1981                 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1982             }
1983             MethodType rawType = mh.type();
1984             if (rawType.parameterType(0) == caller)  return mh;
1985             MethodType narrowType = rawType.changeParameterType(0, caller);
1986             assert(!mh.isVarargsCollector());  // viewAsType will lose varargs-ness
1987             assert(mh.viewAsTypeChecks(narrowType, true));
1988             return mh.copyWith(narrowType, mh.form);
1989         }
1990 
1991         /** Check access and get the requested method. */
1992         private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1993             final boolean doRestrict    = true;
1994             final boolean checkSecurity = true;
1995             return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1996         }
1997         /** Check access and get the requested method, eliding receiver narrowing rules. */
1998         private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1999             final boolean doRestrict    = false;
2000             final boolean checkSecurity = true;
2001             return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2002         }
2003         /** Check access and get the requested method, eliding security manager checks. */
2004         private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2005             final boolean doRestrict    = true;
2006             final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
2007             return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2008         }
2009         /** Common code for all methods; do not call directly except from immediately above. */
2010         private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2011                                                    boolean checkSecurity,
2012                                                    boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2013             checkMethod(refKind, refc, method);
2014             // Optionally check with the security manager; this isn't needed for unreflect* calls.
2015             if (checkSecurity)
2016                 checkSecurityManager(refc, method);
2017             assert(!method.isMethodHandleInvoke());
2018 
2019             if (refKind == REF_invokeSpecial &&
2020                 refc != lookupClass() &&
2021                 !refc.isInterface() &&
2022                 refc != lookupClass().getSuperclass() &&
2023                 refc.isAssignableFrom(lookupClass())) {
2024                 assert(!method.getName().equals("<init>"));  // not this code path
2025                 // Per JVMS 6.5, desc. of invokespecial instruction:
2026                 // If the method is in a superclass of the LC,
2027                 // and if our original search was above LC.super,
2028                 // repeat the search (symbolic lookup) from LC.super
2029                 // and continue with the direct superclass of that class,
2030                 // and so forth, until a match is found or no further superclasses exist.
2031                 // FIXME: MemberName.resolve should handle this instead.
2032                 Class<?> refcAsSuper = lookupClass();
2033                 MemberName m2;
2034                 do {
2035                     refcAsSuper = refcAsSuper.getSuperclass();
2036                     m2 = new MemberName(refcAsSuper,
2037                                         method.getName(),
2038                                         method.getMethodType(),
2039                                         REF_invokeSpecial);
2040                     m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2041                 } while (m2 == null &&         // no method is found yet
2042                          refc != refcAsSuper); // search up to refc
2043                 if (m2 == null)  throw new InternalError(method.toString());
2044                 method = m2;
2045                 refc = refcAsSuper;
2046                 // redo basic checks
2047                 checkMethod(refKind, refc, method);
2048             }
2049 
2050             DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2051             MethodHandle mh = dmh;
2052             // Optionally narrow the receiver argument to refc using restrictReceiver.
2053             if (doRestrict &&
2054                    (refKind == REF_invokeSpecial ||
2055                        (MethodHandleNatives.refKindHasReceiver(refKind) &&
2056                            restrictProtectedReceiver(method)))) {
2057                 mh = restrictReceiver(method, dmh, lookupClass());
2058             }
2059             mh = maybeBindCaller(method, mh, callerClass);
2060             mh = mh.setVarargs(method);
2061             return mh;
2062         }
2063         private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2064                                              Class<?> callerClass)
2065                                              throws IllegalAccessException {
2066             if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2067                 return mh;
2068             Class<?> hostClass = lookupClass;
2069             if (!hasPrivateAccess())  // caller must have private access
2070                 hostClass = callerClass;  // callerClass came from a security manager style stack walk
2071             MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2072             // Note: caller will apply varargs after this step happens.
2073             return cbmh;
2074         }
2075         /** Check access and get the requested field. */
2076         private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2077             final boolean checkSecurity = true;
2078             return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2079         }
2080         /** Check access and get the requested field, eliding security manager checks. */
2081         private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2082             final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
2083             return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2084         }
2085         /** Common code for all fields; do not call directly except from immediately above. */
2086         private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2087                                                   boolean checkSecurity) throws IllegalAccessException {
2088             checkField(refKind, refc, field);
2089             // Optionally check with the security manager; this isn't needed for unreflect* calls.
2090             if (checkSecurity)
2091                 checkSecurityManager(refc, field);
2092             DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2093             boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2094                                     restrictProtectedReceiver(field));
2095             if (doRestrict)
2096                 return restrictReceiver(field, dmh, lookupClass());
2097             return dmh;
2098         }
2099         private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2100                                             Class<?> refc, MemberName getField, MemberName putField)
2101                 throws IllegalAccessException {
2102             final boolean checkSecurity = true;
2103             return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2104         }
2105         private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2106                                                              Class<?> refc, MemberName getField, MemberName putField)
2107                 throws IllegalAccessException {
2108             final boolean checkSecurity = false;
2109             return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2110         }
2111         private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2112                                                   Class<?> refc, MemberName getField, MemberName putField,
2113                                                   boolean checkSecurity) throws IllegalAccessException {
2114             assert getField.isStatic() == putField.isStatic();
2115             assert getField.isGetter() && putField.isSetter();
2116             assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2117             assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2118 
2119             checkField(getRefKind, refc, getField);
2120             if (checkSecurity)
2121                 checkSecurityManager(refc, getField);
2122 
2123             if (!putField.isFinal()) {
2124                 // A VarHandle does not support updates to final fields, any
2125                 // such VarHandle to a final field will be read-only and
2126                 // therefore the following write-based accessibility checks are
2127                 // only required for non-final fields
2128                 checkField(putRefKind, refc, putField);
2129                 if (checkSecurity)
2130                     checkSecurityManager(refc, putField);
2131             }
2132 
2133             boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2134                                   restrictProtectedReceiver(getField));
2135             if (doRestrict) {
2136                 assert !getField.isStatic();
2137                 // receiver type of VarHandle is too wide; narrow to caller
2138                 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2139                     throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2140                 }
2141                 refc = lookupClass();
2142             }
2143             return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2144         }
2145         /** Check access and get the requested constructor. */
2146         private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2147             final boolean checkSecurity = true;
2148             return getDirectConstructorCommon(refc, ctor, checkSecurity);
2149         }
2150         /** Check access and get the requested constructor, eliding security manager checks. */
2151         private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2152             final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
2153             return getDirectConstructorCommon(refc, ctor, checkSecurity);
2154         }
2155         /** Common code for all constructors; do not call directly except from immediately above. */
2156         private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2157                                                   boolean checkSecurity) throws IllegalAccessException {
2158             assert(ctor.isConstructor());
2159             checkAccess(REF_newInvokeSpecial, refc, ctor);
2160             // Optionally check with the security manager; this isn't needed for unreflect* calls.
2161             if (checkSecurity)
2162                 checkSecurityManager(refc, ctor);
2163             assert(!MethodHandleNatives.isCallerSensitive(ctor));  // maybeBindCaller not relevant here
2164             return DirectMethodHandle.make(ctor).setVarargs(ctor);
2165         }
2166 
2167         /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2168          */
2169         /*non-public*/
2170         MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2171             if (!(type instanceof Class || type instanceof MethodType))
2172                 throw new InternalError("unresolved MemberName");
2173             MemberName member = new MemberName(refKind, defc, name, type);
2174             MethodHandle mh = LOOKASIDE_TABLE.get(member);
2175             if (mh != null) {
2176                 checkSymbolicClass(defc);
2177                 return mh;
2178             }
2179             // Treat MethodHandle.invoke and invokeExact specially.
2180             if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2181                 mh = findVirtualForMH(member.getName(), member.getMethodType());
2182                 if (mh != null) {
2183                     return mh;
2184                 }
2185             }
2186             MemberName resolved = resolveOrFail(refKind, member);
2187             mh = getDirectMethodForConstant(refKind, defc, resolved);
2188             if (mh instanceof DirectMethodHandle
2189                     && canBeCached(refKind, defc, resolved)) {
2190                 MemberName key = mh.internalMemberName();
2191                 if (key != null) {
2192                     key = key.asNormalOriginal();
2193                 }
2194                 if (member.equals(key)) {  // better safe than sorry
2195                     LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2196                 }
2197             }
2198             return mh;
2199         }
2200         private
2201         boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2202             if (refKind == REF_invokeSpecial) {
2203                 return false;
2204             }
2205             if (!Modifier.isPublic(defc.getModifiers()) ||
2206                     !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2207                     !member.isPublic() ||
2208                     member.isCallerSensitive()) {
2209                 return false;
2210             }
2211             ClassLoader loader = defc.getClassLoader();
2212             if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2213                 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2214                 boolean found = false;
2215                 while (sysl != null) {
2216                     if (loader == sysl) { found = true; break; }
2217                     sysl = sysl.getParent();
2218                 }
2219                 if (!found) {
2220                     return false;
2221                 }
2222             }
2223             try {
2224                 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2225                     new MemberName(refKind, defc, member.getName(), member.getType()));
2226                 checkSecurityManager(defc, resolved2);
2227             } catch (ReflectiveOperationException | SecurityException ex) {
2228                 return false;
2229             }
2230             return true;
2231         }
2232         private
2233         MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2234                 throws ReflectiveOperationException {
2235             if (MethodHandleNatives.refKindIsField(refKind)) {
2236                 return getDirectFieldNoSecurityManager(refKind, defc, member);
2237             } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2238                 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2239             } else if (refKind == REF_newInvokeSpecial) {
2240                 return getDirectConstructorNoSecurityManager(defc, member);
2241             }
2242             // oops
2243             throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2244         }
2245 
2246         static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2247     }
2248 
2249     /**
2250      * Helper class used to lazily create PUBLIC_LOOKUP with a lookup class
2251      * in an <em>unnamed module</em>.
2252      *
2253      * @see Lookup#publicLookup
2254      */
2255     private static class LookupHelper {
2256         private static final String UNNAMED = "Unnamed";
2257         private static final String OBJECT  = "java/lang/Object";
2258 
2259         private static Class<?> createClass() {
2260             try {
2261                 ClassWriter cw = new ClassWriter(0);
2262                 cw.visit(Opcodes.V1_8,
2263                          Opcodes.ACC_FINAL + Opcodes.ACC_SUPER,
2264                          UNNAMED,
2265                          null,
2266                          OBJECT,
2267                          null);
2268                 cw.visitSource(UNNAMED, null);
2269                 cw.visitEnd();
2270                 byte[] bytes = cw.toByteArray();
2271                 ClassLoader loader = new ClassLoader(null) {
2272                     @Override
2273                     protected Class<?> findClass(String cn) throws ClassNotFoundException {
2274                         if (cn.equals(UNNAMED))
2275                             return super.defineClass(UNNAMED, bytes, 0, bytes.length);
2276                         throw new ClassNotFoundException(cn);
2277                     }
2278                 };
2279                 return loader.loadClass(UNNAMED);
2280             } catch (Exception e) {
2281                 throw new InternalError(e);
2282             }
2283         }
2284 
2285         private static final Class<?> PUBLIC_LOOKUP_CLASS = createClass();
2286 
2287         /**
2288          * Lookup that is trusted minimally. It can only be used to create
2289          * method handles to publicly accessible members in exported packages.
2290          *
2291          * @see MethodHandles#publicLookup
2292          */
2293         static final Lookup PUBLIC_LOOKUP = new Lookup(PUBLIC_LOOKUP_CLASS, Lookup.PUBLIC);
2294     }
2295 
2296     /**
2297      * Produces a method handle constructing arrays of a desired type.
2298      * The return type of the method handle will be the array type.
2299      * The type of its sole argument will be {@code int}, which specifies the size of the array.
2300      * @param arrayClass an array type
2301      * @return a method handle which can create arrays of the given type
2302      * @throws NullPointerException if the argument is {@code null}
2303      * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2304      * @see java.lang.reflect.Array#newInstance(Class, int)
2305      * @since 9
2306      */
2307     public static
2308     MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2309         if (!arrayClass.isArray()) {
2310             throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2311         }
2312         MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2313                 bindTo(arrayClass.getComponentType());
2314         return ani.asType(ani.type().changeReturnType(arrayClass));
2315     }
2316 
2317     /**
2318      * Produces a method handle returning the length of an array.
2319      * The type of the method handle will have {@code int} as return type,
2320      * and its sole argument will be the array type.
2321      * @param arrayClass an array type
2322      * @return a method handle which can retrieve the length of an array of the given array type
2323      * @throws NullPointerException if the argument is {@code null}
2324      * @throws IllegalArgumentException if arrayClass is not an array type
2325      * @since 9
2326      */
2327     public static
2328     MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2329         return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2330     }
2331 
2332     /**
2333      * Produces a method handle giving read access to elements of an array.
2334      * The type of the method handle will have a return type of the array's
2335      * element type.  Its first argument will be the array type,
2336      * and the second will be {@code int}.
2337      * @param arrayClass an array type
2338      * @return a method handle which can load values from the given array type
2339      * @throws NullPointerException if the argument is null
2340      * @throws  IllegalArgumentException if arrayClass is not an array type
2341      */
2342     public static
2343     MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2344         return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2345     }
2346 
2347     /**
2348      * Produces a method handle giving write access to elements of an array.
2349      * The type of the method handle will have a void return type.
2350      * Its last argument will be the array's element type.
2351      * The first and second arguments will be the array type and int.
2352      * @param arrayClass the class of an array
2353      * @return a method handle which can store values into the array type
2354      * @throws NullPointerException if the argument is null
2355      * @throws IllegalArgumentException if arrayClass is not an array type
2356      */
2357     public static
2358     MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2359         return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2360     }
2361 
2362     /**
2363      *
2364      * Produces a VarHandle giving access to elements of an array type
2365      * {@code T[]}, supporting shape {@code (T[], int : T)}.
2366      * <p>
2367      * Certain access modes of the returned VarHandle are unsupported under
2368      * the following conditions:
2369      * <ul>
2370      * <li>if the component type is anything other than {@code byte},
2371      *     {@code short}, {@code char}, {@code int}, {@code long},
2372      *     {@code float}, or {@code double} then numeric atomic update access
2373      *     modes are unsupported.
2374      * <li>if the field type is anything other than {@code boolean},
2375      *     {@code byte}, {@code short}, {@code char}, {@code int} or
2376      *     {@code long} then bitwise atomic update access modes are
2377      *     unsupported.
2378      * </ul>
2379      * <p>
2380      * If the component type is {@code float} or {@code double} then numeric
2381      * and atomic update access modes compare values using their bitwise
2382      * representation (see {@link Float#floatToRawIntBits} and
2383      * {@link Double#doubleToRawLongBits}, respectively).
2384      * @apiNote
2385      * Bitwise comparison of {@code float} values or {@code double} values,
2386      * as performed by the numeric and atomic update access modes, differ
2387      * from the primitive {@code ==} operator and the {@link Float#equals}
2388      * and {@link Double#equals} methods, specifically with respect to
2389      * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2390      * Care should be taken when performing a compare and set or a compare
2391      * and exchange operation with such values since the operation may
2392      * unexpectedly fail.
2393      * There are many possible NaN values that are considered to be
2394      * {@code NaN} in Java, although no IEEE 754 floating-point operation
2395      * provided by Java can distinguish between them.  Operation failure can
2396      * occur if the expected or witness value is a NaN value and it is
2397      * transformed (perhaps in a platform specific manner) into another NaN
2398      * value, and thus has a different bitwise representation (see
2399      * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2400      * details).
2401      * The values {@code -0.0} and {@code +0.0} have different bitwise
2402      * representations but are considered equal when using the primitive
2403      * {@code ==} operator.  Operation failure can occur if, for example, a
2404      * numeric algorithm computes an expected value to be say {@code -0.0}
2405      * and previously computed the witness value to be say {@code +0.0}.
2406      * @param arrayClass the class of an array, of type {@code T[]}
2407      * @return a VarHandle giving access to elements of an array
2408      * @throws NullPointerException if the arrayClass is null
2409      * @throws IllegalArgumentException if arrayClass is not an array type
2410      * @since 9
2411      */
2412     public static
2413     VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2414         return VarHandles.makeArrayElementHandle(arrayClass);
2415     }
2416 
2417     /**
2418      * Produces a VarHandle giving access to elements of a {@code byte[]} array
2419      * viewed as if it were a different primitive array type, such as
2420      * {@code int[]} or {@code long[]}.  The shape of the resulting VarHandle is
2421      * {@code (byte[], int : T)}, where the {@code int} coordinate type
2422      * corresponds to an argument that is an index in a {@code byte[]} array,
2423      * and {@code T} is the component type of the given view array class.  The
2424      * returned VarHandle accesses bytes at an index in a {@code byte[]} array,
2425      * composing bytes to or from a value of {@code T} according to the given
2426      * endianness.
2427      * <p>
2428      * The supported component types (variables types) are {@code short},
2429      * {@code char}, {@code int}, {@code long}, {@code float} and
2430      * {@code double}.
2431      * <p>
2432      * Access of bytes at a given index will result in an
2433      * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2434      * or greater than the {@code byte[]} array length minus the size (in bytes)
2435      * of {@code T}.
2436      * <p>
2437      * Access of bytes at an index may be aligned or misaligned for {@code T},
2438      * with respect to the underlying memory address, {@code A} say, associated
2439      * with the array and index.
2440      * If access is misaligned then access for anything other than the
2441      * {@code get} and {@code set} access modes will result in an
2442      * {@code IllegalStateException}.  In such cases atomic access is only
2443      * guaranteed with respect to the largest power of two that divides the GCD
2444      * of {@code A} and the size (in bytes) of {@code T}.
2445      * If access is aligned then following access modes are supported and are
2446      * guaranteed to support atomic access:
2447      * <ul>
2448      * <li>read write access modes for all {@code T}, with the exception of
2449      *     access modes {@code get} and {@code set} for {@code long} and
2450      *     {@code double} on 32-bit platforms.
2451      * <li>atomic update access modes for {@code int}, {@code long},
2452      *     {@code float} or {@code double}.
2453      *     (Future major platform releases of the JDK may support additional
2454      *     types for certain currently unsupported access modes.)
2455      * <li>numeric atomic update access modes for {@code int} and {@code long}.
2456      *     (Future major platform releases of the JDK may support additional
2457      *     numeric types for certain currently unsupported access modes.)
2458      * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2459      *     (Future major platform releases of the JDK may support additional
2460      *     numeric types for certain currently unsupported access modes.)
2461      * </ul>
2462      * <p>
2463      * Misaligned access, and therefore atomicity guarantees, may be determined
2464      * for {@code byte[]} arrays without operating on a specific array.  Given
2465      * an {@code index}, {@code T} and it's corresponding boxed type,
2466      * {@code T_BOX}, misalignment may be determined as follows:
2467      * <pre>{@code
2468      * int sizeOfT = T_BOX.BYTES;  // size in bytes of T
2469      * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2470      *     alignmentOffset(0, sizeOfT);
2471      * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2472      * boolean isMisaligned = misalignedAtIndex != 0;
2473      * }</pre>
2474      * <p>
2475      * If the variable type is {@code float} or {@code double} then atomic
2476      * update access modes compare values using their bitwise representation
2477      * (see {@link Float#floatToRawIntBits} and
2478      * {@link Double#doubleToRawLongBits}, respectively).
2479      * @param viewArrayClass the view array class, with a component type of
2480      * type {@code T}
2481      * @param byteOrder the endianness of the view array elements, as
2482      * stored in the underlying {@code byte} array
2483      * @return a VarHandle giving access to elements of a {@code byte[]} array
2484      * viewed as if elements corresponding to the components type of the view
2485      * array class
2486      * @throws NullPointerException if viewArrayClass or byteOrder is null
2487      * @throws IllegalArgumentException if viewArrayClass is not an array type
2488      * @throws UnsupportedOperationException if the component type of
2489      * viewArrayClass is not supported as a variable type
2490      * @since 9
2491      */
2492     public static
2493     VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2494                                      ByteOrder byteOrder) throws IllegalArgumentException {
2495         Objects.requireNonNull(byteOrder);
2496         return VarHandles.byteArrayViewHandle(viewArrayClass,
2497                                               byteOrder == ByteOrder.BIG_ENDIAN);
2498     }
2499 
2500     /**
2501      * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2502      * viewed as if it were an array of elements of a different primitive
2503      * component type to that of {@code byte}, such as {@code int[]} or
2504      * {@code long[]}.  The shape of the resulting VarHandle is
2505      * {@code (ByteBuffer, int : T)}, where the {@code int} coordinate type
2506      * corresponds to an argument that is an index in a {@code ByteBuffer}, and
2507      * {@code T} is the component type of the given view array class.  The
2508      * returned VarHandle accesses bytes at an index in a {@code ByteBuffer},
2509      * composing bytes to or from a value of {@code T} according to the given
2510      * endianness.
2511      * <p>
2512      * The supported component types (variables types) are {@code short},
2513      * {@code char}, {@code int}, {@code long}, {@code float} and
2514      * {@code double}.
2515      * <p>
2516      * Access will result in a {@code ReadOnlyBufferException} for anything
2517      * other than the read access modes if the {@code ByteBuffer} is read-only.
2518      * <p>
2519      * Access of bytes at a given index will result in an
2520      * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2521      * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2522      * {@code T}.
2523      * <p>
2524      * Access of bytes at an index may be aligned or misaligned for {@code T},
2525      * with respect to the underlying memory address, {@code A} say, associated
2526      * with the {@code ByteBuffer} and index.
2527      * If access is misaligned then access for anything other than the
2528      * {@code get} and {@code set} access modes will result in an
2529      * {@code IllegalStateException}.  In such cases atomic access is only
2530      * guaranteed with respect to the largest power of two that divides the GCD
2531      * of {@code A} and the size (in bytes) of {@code T}.
2532      * If access is aligned then following access modes are supported and are
2533      * guaranteed to support atomic access:
2534      * <ul>
2535      * <li>read write access modes for all {@code T}, with the exception of
2536      *     access modes {@code get} and {@code set} for {@code long} and
2537      *     {@code double} on 32-bit platforms.
2538      * <li>atomic update access modes for {@code int}, {@code long},
2539      *     {@code float} or {@code double}.
2540      *     (Future major platform releases of the JDK may support additional
2541      *     types for certain currently unsupported access modes.)
2542      * <li>numeric atomic update access modes for {@code int} and {@code long}.
2543      *     (Future major platform releases of the JDK may support additional
2544      *     numeric types for certain currently unsupported access modes.)
2545      * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2546      *     (Future major platform releases of the JDK may support additional
2547      *     numeric types for certain currently unsupported access modes.)
2548      * </ul>
2549      * <p>
2550      * Misaligned access, and therefore atomicity guarantees, may be determined
2551      * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2552      * {@code index}, {@code T} and it's corresponding boxed type,
2553      * {@code T_BOX}, as follows:
2554      * <pre>{@code
2555      * int sizeOfT = T_BOX.BYTES;  // size in bytes of T
2556      * ByteBuffer bb = ...
2557      * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2558      * boolean isMisaligned = misalignedAtIndex != 0;
2559      * }</pre>
2560      * <p>
2561      * If the variable type is {@code float} or {@code double} then atomic
2562      * update access modes compare values using their bitwise representation
2563      * (see {@link Float#floatToRawIntBits} and
2564      * {@link Double#doubleToRawLongBits}, respectively).
2565      * @param viewArrayClass the view array class, with a component type of
2566      * type {@code T}
2567      * @param byteOrder the endianness of the view array elements, as
2568      * stored in the underlying {@code ByteBuffer} (Note this overrides the
2569      * endianness of a {@code ByteBuffer})
2570      * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2571      * viewed as if elements corresponding to the components type of the view
2572      * array class
2573      * @throws NullPointerException if viewArrayClass or byteOrder is null
2574      * @throws IllegalArgumentException if viewArrayClass is not an array type
2575      * @throws UnsupportedOperationException if the component type of
2576      * viewArrayClass is not supported as a variable type
2577      * @since 9
2578      */
2579     public static
2580     VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2581                                       ByteOrder byteOrder) throws IllegalArgumentException {
2582         Objects.requireNonNull(byteOrder);
2583         return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2584                                                    byteOrder == ByteOrder.BIG_ENDIAN);
2585     }
2586 
2587 
2588     /// method handle invocation (reflective style)
2589 
2590     /**
2591      * Produces a method handle which will invoke any method handle of the
2592      * given {@code type}, with a given number of trailing arguments replaced by
2593      * a single trailing {@code Object[]} array.
2594      * The resulting invoker will be a method handle with the following
2595      * arguments:
2596      * <ul>
2597      * <li>a single {@code MethodHandle} target
2598      * <li>zero or more leading values (counted by {@code leadingArgCount})
2599      * <li>an {@code Object[]} array containing trailing arguments
2600      * </ul>
2601      * <p>
2602      * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2603      * the indicated {@code type}.
2604      * That is, if the target is exactly of the given {@code type}, it will behave
2605      * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2606      * is used to convert the target to the required {@code type}.
2607      * <p>
2608      * The type of the returned invoker will not be the given {@code type}, but rather
2609      * will have all parameters except the first {@code leadingArgCount}
2610      * replaced by a single array of type {@code Object[]}, which will be
2611      * the final parameter.
2612      * <p>
2613      * Before invoking its target, the invoker will spread the final array, apply
2614      * reference casts as necessary, and unbox and widen primitive arguments.
2615      * If, when the invoker is called, the supplied array argument does
2616      * not have the correct number of elements, the invoker will throw
2617      * an {@link IllegalArgumentException} instead of invoking the target.
2618      * <p>
2619      * This method is equivalent to the following code (though it may be more efficient):
2620      * <blockquote><pre>{@code
2621 MethodHandle invoker = MethodHandles.invoker(type);
2622 int spreadArgCount = type.parameterCount() - leadingArgCount;
2623 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2624 return invoker;
2625      * }</pre></blockquote>
2626      * This method throws no reflective or security exceptions.
2627      * @param type the desired target type
2628      * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2629      * @return a method handle suitable for invoking any method handle of the given type
2630      * @throws NullPointerException if {@code type} is null
2631      * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2632      *                  the range from 0 to {@code type.parameterCount()} inclusive,
2633      *                  or if the resulting method handle's type would have
2634      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
2635      */
2636     public static
2637     MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2638         if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2639             throw newIllegalArgumentException("bad argument count", leadingArgCount);
2640         type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2641         return type.invokers().spreadInvoker(leadingArgCount);
2642     }
2643 
2644     /**
2645      * Produces a special <em>invoker method handle</em> which can be used to
2646      * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2647      * The resulting invoker will have a type which is
2648      * exactly equal to the desired type, except that it will accept
2649      * an additional leading argument of type {@code MethodHandle}.
2650      * <p>
2651      * This method is equivalent to the following code (though it may be more efficient):
2652      * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2653      *
2654      * <p style="font-size:smaller;">
2655      * <em>Discussion:</em>
2656      * Invoker method handles can be useful when working with variable method handles
2657      * of unknown types.
2658      * For example, to emulate an {@code invokeExact} call to a variable method
2659      * handle {@code M}, extract its type {@code T},
2660      * look up the invoker method {@code X} for {@code T},
2661      * and call the invoker method, as {@code X.invoke(T, A...)}.
2662      * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2663      * is unknown.)
2664      * If spreading, collecting, or other argument transformations are required,
2665      * they can be applied once to the invoker {@code X} and reused on many {@code M}
2666      * method handle values, as long as they are compatible with the type of {@code X}.
2667      * <p style="font-size:smaller;">
2668      * <em>(Note:  The invoker method is not available via the Core Reflection API.
2669      * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2670      * on the declared {@code invokeExact} or {@code invoke} method will raise an
2671      * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2672      * <p>
2673      * This method throws no reflective or security exceptions.
2674      * @param type the desired target type
2675      * @return a method handle suitable for invoking any method handle of the given type
2676      * @throws IllegalArgumentException if the resulting method handle's type would have
2677      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
2678      */
2679     public static
2680     MethodHandle exactInvoker(MethodType type) {
2681         return type.invokers().exactInvoker();
2682     }
2683 
2684     /**
2685      * Produces a special <em>invoker method handle</em> which can be used to
2686      * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2687      * The resulting invoker will have a type which is
2688      * exactly equal to the desired type, except that it will accept
2689      * an additional leading argument of type {@code MethodHandle}.
2690      * <p>
2691      * Before invoking its target, if the target differs from the expected type,
2692      * the invoker will apply reference casts as
2693      * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2694      * Similarly, the return value will be converted as necessary.
2695      * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2696      * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2697      * <p>
2698      * This method is equivalent to the following code (though it may be more efficient):
2699      * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2700      * <p style="font-size:smaller;">
2701      * <em>Discussion:</em>
2702      * A {@linkplain MethodType#genericMethodType general method type} is one which
2703      * mentions only {@code Object} arguments and return values.
2704      * An invoker for such a type is capable of calling any method handle
2705      * of the same arity as the general type.
2706      * <p style="font-size:smaller;">
2707      * <em>(Note:  The invoker method is not available via the Core Reflection API.
2708      * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2709      * on the declared {@code invokeExact} or {@code invoke} method will raise an
2710      * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2711      * <p>
2712      * This method throws no reflective or security exceptions.
2713      * @param type the desired target type
2714      * @return a method handle suitable for invoking any method handle convertible to the given type
2715      * @throws IllegalArgumentException if the resulting method handle's type would have
2716      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
2717      */
2718     public static
2719     MethodHandle invoker(MethodType type) {
2720         return type.invokers().genericInvoker();
2721     }
2722 
2723     /**
2724      * Produces a special <em>invoker method handle</em> which can be used to
2725      * invoke a signature-polymorphic access mode method on any VarHandle whose
2726      * associated access mode type is compatible with the given type.
2727      * The resulting invoker will have a type which is exactly equal to the
2728      * desired given type, except that it will accept an additional leading
2729      * argument of type {@code VarHandle}.
2730      *
2731      * @param accessMode the VarHandle access mode
2732      * @param type the desired target type
2733      * @return a method handle suitable for invoking an access mode method of
2734      *         any VarHandle whose access mode type is of the given type.
2735      * @since 9
2736      */
2737     static public
2738     MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2739         return type.invokers().varHandleMethodExactInvoker(accessMode);
2740     }
2741 
2742     /**
2743      * Produces a special <em>invoker method handle</em> which can be used to
2744      * invoke a signature-polymorphic access mode method on any VarHandle whose
2745      * associated access mode type is compatible with the given type.
2746      * The resulting invoker will have a type which is exactly equal to the
2747      * desired given type, except that it will accept an additional leading
2748      * argument of type {@code VarHandle}.
2749      * <p>
2750      * Before invoking its target, if the access mode type differs from the
2751      * desired given type, the invoker will apply reference casts as necessary
2752      * and box, unbox, or widen primitive values, as if by
2753      * {@link MethodHandle#asType asType}.  Similarly, the return value will be
2754      * converted as necessary.
2755      * <p>
2756      * This method is equivalent to the following code (though it may be more
2757      * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2758      *
2759      * @param accessMode the VarHandle access mode
2760      * @param type the desired target type
2761      * @return a method handle suitable for invoking an access mode method of
2762      *         any VarHandle whose access mode type is convertible to the given
2763      *         type.
2764      * @since 9
2765      */
2766     static public
2767     MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2768         return type.invokers().varHandleMethodInvoker(accessMode);
2769     }
2770 
2771     static /*non-public*/
2772     MethodHandle basicInvoker(MethodType type) {
2773         return type.invokers().basicInvoker();
2774     }
2775 
2776      /// method handle modification (creation from other method handles)
2777 
2778     /**
2779      * Produces a method handle which adapts the type of the
2780      * given method handle to a new type by pairwise argument and return type conversion.
2781      * The original type and new type must have the same number of arguments.
2782      * The resulting method handle is guaranteed to report a type
2783      * which is equal to the desired new type.
2784      * <p>
2785      * If the original type and new type are equal, returns target.
2786      * <p>
2787      * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
2788      * and some additional conversions are also applied if those conversions fail.
2789      * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
2790      * if possible, before or instead of any conversions done by {@code asType}:
2791      * <ul>
2792      * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
2793      *     then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2794      *     (This treatment of interfaces follows the usage of the bytecode verifier.)
2795      * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2796      *     the boolean is converted to a byte value, 1 for true, 0 for false.
2797      *     (This treatment follows the usage of the bytecode verifier.)
2798      * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2799      *     <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2800      *     and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2801      * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2802      *     then a Java casting conversion (JLS 5.5) is applied.
2803      *     (Specifically, <em>T0</em> will convert to <em>T1</em> by
2804      *     widening and/or narrowing.)
2805      * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2806      *     conversion will be applied at runtime, possibly followed
2807      *     by a Java casting conversion (JLS 5.5) on the primitive value,
2808      *     possibly followed by a conversion from byte to boolean by testing
2809      *     the low-order bit.
2810      * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2811      *     and if the reference is null at runtime, a zero value is introduced.
2812      * </ul>
2813      * @param target the method handle to invoke after arguments are retyped
2814      * @param newType the expected type of the new method handle
2815      * @return a method handle which delegates to the target after performing
2816      *           any necessary argument conversions, and arranges for any
2817      *           necessary return value conversions
2818      * @throws NullPointerException if either argument is null
2819      * @throws WrongMethodTypeException if the conversion cannot be made
2820      * @see MethodHandle#asType
2821      */
2822     public static
2823     MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2824         explicitCastArgumentsChecks(target, newType);
2825         // use the asTypeCache when possible:
2826         MethodType oldType = target.type();
2827         if (oldType == newType)  return target;
2828         if (oldType.explicitCastEquivalentToAsType(newType)) {
2829             return target.asFixedArity().asType(newType);
2830         }
2831         return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2832     }
2833 
2834     private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2835         if (target.type().parameterCount() != newType.parameterCount()) {
2836             throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2837         }
2838     }
2839 
2840     /**
2841      * Produces a method handle which adapts the calling sequence of the
2842      * given method handle to a new type, by reordering the arguments.
2843      * The resulting method handle is guaranteed to report a type
2844      * which is equal to the desired new type.
2845      * <p>
2846      * The given array controls the reordering.
2847      * Call {@code #I} the number of incoming parameters (the value
2848      * {@code newType.parameterCount()}, and call {@code #O} the number
2849      * of outgoing parameters (the value {@code target.type().parameterCount()}).
2850      * Then the length of the reordering array must be {@code #O},
2851      * and each element must be a non-negative number less than {@code #I}.
2852      * For every {@code N} less than {@code #O}, the {@code N}-th
2853      * outgoing argument will be taken from the {@code I}-th incoming
2854      * argument, where {@code I} is {@code reorder[N]}.
2855      * <p>
2856      * No argument or return value conversions are applied.
2857      * The type of each incoming argument, as determined by {@code newType},
2858      * must be identical to the type of the corresponding outgoing parameter
2859      * or parameters in the target method handle.
2860      * The return type of {@code newType} must be identical to the return
2861      * type of the original target.
2862      * <p>
2863      * The reordering array need not specify an actual permutation.
2864      * An incoming argument will be duplicated if its index appears
2865      * more than once in the array, and an incoming argument will be dropped
2866      * if its index does not appear in the array.
2867      * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2868      * incoming arguments which are not mentioned in the reordering array
2869      * may be of any type, as determined only by {@code newType}.
2870      * <blockquote><pre>{@code
2871 import static java.lang.invoke.MethodHandles.*;
2872 import static java.lang.invoke.MethodType.*;
2873 ...
2874 MethodType intfn1 = methodType(int.class, int.class);
2875 MethodType intfn2 = methodType(int.class, int.class, int.class);
2876 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2877 assert(sub.type().equals(intfn2));
2878 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2879 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2880 assert((int)rsub.invokeExact(1, 100) == 99);
2881 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2882 assert(add.type().equals(intfn2));
2883 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2884 assert(twice.type().equals(intfn1));
2885 assert((int)twice.invokeExact(21) == 42);
2886      * }</pre></blockquote>
2887      * <p>
2888      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
2889      * variable-arity method handle}, even if the original target method handle was.
2890      * @param target the method handle to invoke after arguments are reordered
2891      * @param newType the expected type of the new method handle
2892      * @param reorder an index array which controls the reordering
2893      * @return a method handle which delegates to the target after it
2894      *           drops unused arguments and moves and/or duplicates the other arguments
2895      * @throws NullPointerException if any argument is null
2896      * @throws IllegalArgumentException if the index array length is not equal to
2897      *                  the arity of the target, or if any index array element
2898      *                  not a valid index for a parameter of {@code newType},
2899      *                  or if two corresponding parameter types in
2900      *                  {@code target.type()} and {@code newType} are not identical,
2901      */
2902     public static
2903     MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2904         reorder = reorder.clone();  // get a private copy
2905         MethodType oldType = target.type();
2906         permuteArgumentChecks(reorder, newType, oldType);
2907         // first detect dropped arguments and handle them separately
2908         int[] originalReorder = reorder;
2909         BoundMethodHandle result = target.rebind();
2910         LambdaForm form = result.form;
2911         int newArity = newType.parameterCount();
2912         // Normalize the reordering into a real permutation,
2913         // by removing duplicates and adding dropped elements.
2914         // This somewhat improves lambda form caching, as well
2915         // as simplifying the transform by breaking it up into steps.
2916         for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
2917             if (ddIdx > 0) {
2918                 // We found a duplicated entry at reorder[ddIdx].
2919                 // Example:  (x,y,z)->asList(x,y,z)
2920                 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
2921                 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
2922                 // The starred element corresponds to the argument
2923                 // deleted by the dupArgumentForm transform.
2924                 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
2925                 boolean killFirst = false;
2926                 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
2927                     // Set killFirst if the dup is larger than an intervening position.
2928                     // This will remove at least one inversion from the permutation.
2929                     if (dupVal > val) killFirst = true;
2930                 }
2931                 if (!killFirst) {
2932                     srcPos = dstPos;
2933                     dstPos = ddIdx;
2934                 }
2935                 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
2936                 assert (reorder[srcPos] == reorder[dstPos]);
2937                 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
2938                 // contract the reordering by removing the element at dstPos
2939                 int tailPos = dstPos + 1;
2940                 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
2941                 reorder = Arrays.copyOf(reorder, reorder.length - 1);
2942             } else {
2943                 int dropVal = ~ddIdx, insPos = 0;
2944                 while (insPos < reorder.length && reorder[insPos] < dropVal) {
2945                     // Find first element of reorder larger than dropVal.
2946                     // This is where we will insert the dropVal.
2947                     insPos += 1;
2948                 }
2949                 Class<?> ptype = newType.parameterType(dropVal);
2950                 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
2951                 oldType = oldType.insertParameterTypes(insPos, ptype);
2952                 // expand the reordering by inserting an element at insPos
2953                 int tailPos = insPos + 1;
2954                 reorder = Arrays.copyOf(reorder, reorder.length + 1);
2955                 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
2956                 reorder[insPos] = dropVal;
2957             }
2958             assert (permuteArgumentChecks(reorder, newType, oldType));
2959         }
2960         assert (reorder.length == newArity);  // a perfect permutation
2961         // Note:  This may cache too many distinct LFs. Consider backing off to varargs code.
2962         form = form.editor().permuteArgumentsForm(1, reorder);
2963         if (newType == result.type() && form == result.internalForm())
2964             return result;
2965         return result.copyWith(newType, form);
2966     }
2967 
2968     /**
2969      * Return an indication of any duplicate or omission in reorder.
2970      * If the reorder contains a duplicate entry, return the index of the second occurrence.
2971      * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
2972      * Otherwise, return zero.
2973      * If an element not in [0..newArity-1] is encountered, return reorder.length.
2974      */
2975     private static int findFirstDupOrDrop(int[] reorder, int newArity) {
2976         final int BIT_LIMIT = 63;  // max number of bits in bit mask
2977         if (newArity < BIT_LIMIT) {
2978             long mask = 0;
2979             for (int i = 0; i < reorder.length; i++) {
2980                 int arg = reorder[i];
2981                 if (arg >= newArity) {
2982                     return reorder.length;
2983                 }
2984                 long bit = 1L << arg;
2985                 if ((mask & bit) != 0) {
2986                     return i;  // >0 indicates a dup
2987                 }
2988                 mask |= bit;
2989             }
2990             if (mask == (1L << newArity) - 1) {
2991                 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2992                 return 0;
2993             }
2994             // find first zero
2995             long zeroBit = Long.lowestOneBit(~mask);
2996             int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2997             assert(zeroPos <= newArity);
2998             if (zeroPos == newArity) {
2999                 return 0;
3000             }
3001             return ~zeroPos;
3002         } else {
3003             // same algorithm, different bit set
3004             BitSet mask = new BitSet(newArity);
3005             for (int i = 0; i < reorder.length; i++) {
3006                 int arg = reorder[i];
3007                 if (arg >= newArity) {
3008                     return reorder.length;
3009                 }
3010                 if (mask.get(arg)) {
3011                     return i;  // >0 indicates a dup
3012                 }
3013                 mask.set(arg);
3014             }
3015             int zeroPos = mask.nextClearBit(0);
3016             assert(zeroPos <= newArity);
3017             if (zeroPos == newArity) {
3018                 return 0;
3019             }
3020             return ~zeroPos;
3021         }
3022     }
3023 
3024     private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3025         if (newType.returnType() != oldType.returnType())
3026             throw newIllegalArgumentException("return types do not match",
3027                     oldType, newType);
3028         if (reorder.length == oldType.parameterCount()) {
3029             int limit = newType.parameterCount();
3030             boolean bad = false;
3031             for (int j = 0; j < reorder.length; j++) {
3032                 int i = reorder[j];
3033                 if (i < 0 || i >= limit) {
3034                     bad = true; break;
3035                 }
3036                 Class<?> src = newType.parameterType(i);
3037                 Class<?> dst = oldType.parameterType(j);
3038                 if (src != dst)
3039                     throw newIllegalArgumentException("parameter types do not match after reorder",
3040                             oldType, newType);
3041             }
3042             if (!bad)  return true;
3043         }
3044         throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3045     }
3046 
3047     /**
3048      * Produces a method handle of the requested return type which returns the given
3049      * constant value every time it is invoked.
3050      * <p>
3051      * Before the method handle is returned, the passed-in value is converted to the requested type.
3052      * If the requested type is primitive, widening primitive conversions are attempted,
3053      * else reference conversions are attempted.
3054      * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3055      * @param type the return type of the desired method handle
3056      * @param value the value to return
3057      * @return a method handle of the given return type and no arguments, which always returns the given value
3058      * @throws NullPointerException if the {@code type} argument is null
3059      * @throws ClassCastException if the value cannot be converted to the required return type
3060      * @throws IllegalArgumentException if the given type is {@code void.class}
3061      */
3062     public static
3063     MethodHandle constant(Class<?> type, Object value) {
3064         if (type.isPrimitive()) {
3065             if (type == void.class)
3066                 throw newIllegalArgumentException("void type");
3067             Wrapper w = Wrapper.forPrimitiveType(type);
3068             value = w.convert(value, type);
3069             if (w.zero().equals(value))
3070                 return zero(w, type);
3071             return insertArguments(identity(type), 0, value);
3072         } else {
3073             if (value == null)
3074                 return zero(Wrapper.OBJECT, type);
3075             return identity(type).bindTo(value);
3076         }
3077     }
3078 
3079     /**
3080      * Produces a method handle which returns its sole argument when invoked.
3081      * @param type the type of the sole parameter and return value of the desired method handle
3082      * @return a unary method handle which accepts and returns the given type
3083      * @throws NullPointerException if the argument is null
3084      * @throws IllegalArgumentException if the given type is {@code void.class}
3085      */
3086     public static
3087     MethodHandle identity(Class<?> type) {
3088         Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3089         int pos = btw.ordinal();
3090         MethodHandle ident = IDENTITY_MHS[pos];
3091         if (ident == null) {
3092             ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3093         }
3094         if (ident.type().returnType() == type)
3095             return ident;
3096         // something like identity(Foo.class); do not bother to intern these
3097         assert (btw == Wrapper.OBJECT);
3098         return makeIdentity(type);
3099     }
3100 
3101     /**
3102      * Produces a constant method handle of the requested return type which
3103      * returns the default value for that type every time it is invoked.
3104      * The resulting constant method handle will have no side effects.
3105      * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3106      * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3107      * since {@code explicitCastArguments} converts {@code null} to default values.
3108      * @param type the expected return type of the desired method handle
3109      * @return a constant method handle that takes no arguments
3110      *         and returns the default value of the given type (or void, if the type is void)
3111      * @throws NullPointerException if the argument is null
3112      * @see MethodHandles#constant
3113      * @see MethodHandles#empty
3114      * @see MethodHandles#explicitCastArguments
3115      * @since 9
3116      */
3117     public static  MethodHandle zero(Class<?> type) {
3118         Objects.requireNonNull(type);
3119         return type.isPrimitive() ?  zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3120     }
3121 
3122     private static MethodHandle identityOrVoid(Class<?> type) {
3123         return type == void.class ? zero(type) : identity(type);
3124     }
3125 
3126     /**
3127      * Produces a method handle of the requested type which ignores any arguments, does nothing,
3128      * and returns a suitable default depending on the return type.
3129      * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3130      * <p>The returned method handle is equivalent to
3131      * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3132      * <p>
3133      * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3134      * {@code guardWithTest(pred, target, empty(target.type())}.
3135      * @param type the type of the desired method handle
3136      * @return a constant method handle of the given type, which returns a default value of the given return type
3137      * @throws NullPointerException if the argument is null
3138      * @see MethodHandles#zero
3139      * @see MethodHandles#constant
3140      * @since 9
3141      */
3142     public static  MethodHandle empty(MethodType type) {
3143         Objects.requireNonNull(type);
3144         return dropArguments(zero(type.returnType()), 0, type.parameterList());
3145     }
3146 
3147     private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3148     private static MethodHandle makeIdentity(Class<?> ptype) {
3149         MethodType mtype = methodType(ptype, ptype);
3150         LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3151         return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3152     }
3153 
3154     private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3155         int pos = btw.ordinal();
3156         MethodHandle zero = ZERO_MHS[pos];
3157         if (zero == null) {
3158             zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3159         }
3160         if (zero.type().returnType() == rtype)
3161             return zero;
3162         assert(btw == Wrapper.OBJECT);
3163         return makeZero(rtype);
3164     }
3165     private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3166     private static MethodHandle makeZero(Class<?> rtype) {
3167         MethodType mtype = methodType(rtype);
3168         LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3169         return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3170     }
3171 
3172     private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3173         // Simulate a CAS, to avoid racy duplication of results.
3174         MethodHandle prev = cache[pos];
3175         if (prev != null) return prev;
3176         return cache[pos] = value;
3177     }
3178 
3179     /**
3180      * Provides a target method handle with one or more <em>bound arguments</em>
3181      * in advance of the method handle's invocation.
3182      * The formal parameters to the target corresponding to the bound
3183      * arguments are called <em>bound parameters</em>.
3184      * Returns a new method handle which saves away the bound arguments.
3185      * When it is invoked, it receives arguments for any non-bound parameters,
3186      * binds the saved arguments to their corresponding parameters,
3187      * and calls the original target.
3188      * <p>
3189      * The type of the new method handle will drop the types for the bound
3190      * parameters from the original target type, since the new method handle
3191      * will no longer require those arguments to be supplied by its callers.
3192      * <p>
3193      * Each given argument object must match the corresponding bound parameter type.
3194      * If a bound parameter type is a primitive, the argument object
3195      * must be a wrapper, and will be unboxed to produce the primitive value.
3196      * <p>
3197      * The {@code pos} argument selects which parameters are to be bound.
3198      * It may range between zero and <i>N-L</i> (inclusively),
3199      * where <i>N</i> is the arity of the target method handle
3200      * and <i>L</i> is the length of the values array.
3201      * <p>
3202      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3203      * variable-arity method handle}, even if the original target method handle was.
3204      * @param target the method handle to invoke after the argument is inserted
3205      * @param pos where to insert the argument (zero for the first)
3206      * @param values the series of arguments to insert
3207      * @return a method handle which inserts an additional argument,
3208      *         before calling the original method handle
3209      * @throws NullPointerException if the target or the {@code values} array is null
3210      * @see MethodHandle#bindTo
3211      */
3212     public static
3213     MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3214         int insCount = values.length;
3215         Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3216         if (insCount == 0)  return target;
3217         BoundMethodHandle result = target.rebind();
3218         for (int i = 0; i < insCount; i++) {
3219             Object value = values[i];
3220             Class<?> ptype = ptypes[pos+i];
3221             if (ptype.isPrimitive()) {
3222                 result = insertArgumentPrimitive(result, pos, ptype, value);
3223             } else {
3224                 value = ptype.cast(value);  // throw CCE if needed
3225                 result = result.bindArgumentL(pos, value);
3226             }
3227         }
3228         return result;
3229     }
3230 
3231     private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3232                                                              Class<?> ptype, Object value) {
3233         Wrapper w = Wrapper.forPrimitiveType(ptype);
3234         // perform unboxing and/or primitive conversion
3235         value = w.convert(value, ptype);
3236         switch (w) {
3237         case INT:     return result.bindArgumentI(pos, (int)value);
3238         case LONG:    return result.bindArgumentJ(pos, (long)value);
3239         case FLOAT:   return result.bindArgumentF(pos, (float)value);
3240         case DOUBLE:  return result.bindArgumentD(pos, (double)value);
3241         default:      return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3242         }
3243     }
3244 
3245     private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3246         MethodType oldType = target.type();
3247         int outargs = oldType.parameterCount();
3248         int inargs  = outargs - insCount;
3249         if (inargs < 0)
3250             throw newIllegalArgumentException("too many values to insert");
3251         if (pos < 0 || pos > inargs)
3252             throw newIllegalArgumentException("no argument type to append");
3253         return oldType.ptypes();
3254     }
3255 
3256     /**
3257      * Produces a method handle which will discard some dummy arguments
3258      * before calling some other specified <i>target</i> method handle.
3259      * The type of the new method handle will be the same as the target's type,
3260      * except it will also include the dummy argument types,
3261      * at some given position.
3262      * <p>
3263      * The {@code pos} argument may range between zero and <i>N</i>,
3264      * where <i>N</i> is the arity of the target.
3265      * If {@code pos} is zero, the dummy arguments will precede
3266      * the target's real arguments; if {@code pos} is <i>N</i>
3267      * they will come after.
3268      * <p>
3269      * <b>Example:</b>
3270      * <blockquote><pre>{@code
3271 import static java.lang.invoke.MethodHandles.*;
3272 import static java.lang.invoke.MethodType.*;
3273 ...
3274 MethodHandle cat = lookup().findVirtual(String.class,
3275   "concat", methodType(String.class, String.class));
3276 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3277 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3278 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3279 assertEquals(bigType, d0.type());
3280 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3281      * }</pre></blockquote>
3282      * <p>
3283      * This method is also equivalent to the following code:
3284      * <blockquote><pre>
3285      * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3286      * </pre></blockquote>
3287      * @param target the method handle to invoke after the arguments are dropped
3288      * @param valueTypes the type(s) of the argument(s) to drop
3289      * @param pos position of first argument to drop (zero for the leftmost)
3290      * @return a method handle which drops arguments of the given types,
3291      *         before calling the original method handle
3292      * @throws NullPointerException if the target is null,
3293      *                              or if the {@code valueTypes} list or any of its elements is null
3294      * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3295      *                  or if {@code pos} is negative or greater than the arity of the target,
3296      *                  or if the new method handle's type would have too many parameters
3297      */
3298     public static
3299     MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3300         return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3301     }
3302 
3303     private static List<Class<?>> copyTypes(Object[] array) {
3304         return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3305     }
3306 
3307     private static
3308     MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3309         MethodType oldType = target.type();  // get NPE
3310         int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3311         MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3312         if (dropped == 0)  return target;
3313         BoundMethodHandle result = target.rebind();
3314         LambdaForm lform = result.form;
3315         int insertFormArg = 1 + pos;
3316         for (Class<?> ptype : valueTypes) {
3317             lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3318         }
3319         result = result.copyWith(newType, lform);
3320         return result;
3321     }
3322 
3323     private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3324         int dropped = valueTypes.size();
3325         MethodType.checkSlotCount(dropped);
3326         int outargs = oldType.parameterCount();
3327         int inargs  = outargs + dropped;
3328         if (pos < 0 || pos > outargs)
3329             throw newIllegalArgumentException("no argument type to remove"
3330                     + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3331                     );
3332         return dropped;
3333     }
3334 
3335     /**
3336      * Produces a method handle which will discard some dummy arguments
3337      * before calling some other specified <i>target</i> method handle.
3338      * The type of the new method handle will be the same as the target's type,
3339      * except it will also include the dummy argument types,
3340      * at some given position.
3341      * <p>
3342      * The {@code pos} argument may range between zero and <i>N</i>,
3343      * where <i>N</i> is the arity of the target.
3344      * If {@code pos} is zero, the dummy arguments will precede
3345      * the target's real arguments; if {@code pos} is <i>N</i>
3346      * they will come after.
3347      * @apiNote
3348      * <blockquote><pre>{@code
3349 import static java.lang.invoke.MethodHandles.*;
3350 import static java.lang.invoke.MethodType.*;
3351 ...
3352 MethodHandle cat = lookup().findVirtual(String.class,
3353   "concat", methodType(String.class, String.class));
3354 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3355 MethodHandle d0 = dropArguments(cat, 0, String.class);
3356 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3357 MethodHandle d1 = dropArguments(cat, 1, String.class);
3358 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3359 MethodHandle d2 = dropArguments(cat, 2, String.class);
3360 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3361 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3362 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3363      * }</pre></blockquote>
3364      * <p>
3365      * This method is also equivalent to the following code:
3366      * <blockquote><pre>
3367      * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3368      * </pre></blockquote>
3369      * @param target the method handle to invoke after the arguments are dropped
3370      * @param valueTypes the type(s) of the argument(s) to drop
3371      * @param pos position of first argument to drop (zero for the leftmost)
3372      * @return a method handle which drops arguments of the given types,
3373      *         before calling the original method handle
3374      * @throws NullPointerException if the target is null,
3375      *                              or if the {@code valueTypes} array or any of its elements is null
3376      * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3377      *                  or if {@code pos} is negative or greater than the arity of the target,
3378      *                  or if the new method handle's type would have
3379      *                  <a href="MethodHandle.html#maxarity">too many parameters</a>
3380      */
3381     public static
3382     MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3383         return dropArguments0(target, pos, copyTypes(valueTypes));
3384     }
3385 
3386     // private version which allows caller some freedom with error handling
3387     private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3388                                       boolean nullOnFailure) {
3389         newTypes = copyTypes(newTypes.toArray());
3390         List<Class<?>> oldTypes = target.type().parameterList();
3391         int match = oldTypes.size();
3392         if (skip != 0) {
3393             if (skip < 0 || skip > match) {
3394                 throw newIllegalArgumentException("illegal skip", skip, target);
3395             }
3396             oldTypes = oldTypes.subList(skip, match);
3397             match -= skip;
3398         }
3399         List<Class<?>> addTypes = newTypes;
3400         int add = addTypes.size();
3401         if (pos != 0) {
3402             if (pos < 0 || pos > add) {
3403                 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3404             }
3405             addTypes = addTypes.subList(pos, add);
3406             add -= pos; assert(addTypes.size() == add);
3407         }
3408         // Do not add types which already match the existing arguments.
3409         if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3410             if (nullOnFailure) {
3411                 return null;
3412             }
3413             throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3414         }
3415         addTypes = addTypes.subList(match, add);
3416         add -= match; assert(addTypes.size() == add);
3417         // newTypes:     (   P*[pos], M*[match], A*[add] )
3418         // target: ( S*[skip],        M*[match]  )
3419         MethodHandle adapter = target;
3420         if (add > 0) {
3421             adapter = dropArguments0(adapter, skip+ match, addTypes);
3422         }
3423         // adapter: (S*[skip],        M*[match], A*[add] )
3424         if (pos > 0) {
3425             adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3426        }
3427         // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3428         return adapter;
3429     }
3430 
3431     /**
3432      * Adapts a target method handle to match the given parameter type list, if necessary, by adding dummy arguments.
3433      * Some leading parameters are first skipped; they will be left unchanged and are otherwise ignored.
3434      * The remaining types in the target's parameter type list must be contained as a sub-list of the given type list,
3435      * at the given position.
3436      * Any non-matching parameter types (before or after the matching sub-list) are inserted in corresponding
3437      * positions of the target method handle's parameters, as if by {@link #dropArguments}.
3438      * (More precisely, elements in the new list before {@code pos} are inserted into the target list at {@code skip},
3439      * while elements in the new list after the match beginning at {@code pos} are inserted at the end of the
3440      * target list.)
3441      * The target's return type will be unchanged.
3442      * @apiNote
3443      * Two method handles whose argument lists are "effectively identical" (i.e., identical
3444      * in a common prefix) may be mutually converted to a common type
3445      * by two calls to {@code dropArgumentsToMatch}, as follows:
3446      * <blockquote><pre>{@code
3447 import static java.lang.invoke.MethodHandles.*;
3448 import static java.lang.invoke.MethodType.*;
3449 ...
3450 ...
3451 MethodHandle h0 = constant(boolean.class, true);
3452 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3453 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3454 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3455 if (h1.type().parameterCount() < h2.type().parameterCount())
3456     h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0);  // lengthen h1
3457 else
3458     h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0);    // lengthen h2
3459 MethodHandle h3 = guardWithTest(h0, h1, h2);
3460 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3461      * }</pre></blockquote>
3462      * @param target the method handle to adapt
3463      * @param skip number of targets parameters to disregard (they will be unchanged)
3464      * @param newTypes the desired argument list of the method handle
3465      * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3466      * @return a possibly adapted method handle
3467      * @throws NullPointerException if either argument is null
3468      * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3469      *         or if {@code skip} is negative or greater than the arity of the target,
3470      *         or if {@code pos} is negative or greater than the newTypes list size,
3471      *         or if the non-skipped target parameter types match the new types at {@code pos}
3472      * @since 9
3473      */
3474     public static
3475     MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3476         Objects.requireNonNull(target);
3477         Objects.requireNonNull(newTypes);
3478         return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3479     }
3480 
3481     /**
3482      * Adapts a target method handle by pre-processing
3483      * one or more of its arguments, each with its own unary filter function,
3484      * and then calling the target with each pre-processed argument
3485      * replaced by the result of its corresponding filter function.
3486      * <p>
3487      * The pre-processing is performed by one or more method handles,
3488      * specified in the elements of the {@code filters} array.
3489      * The first element of the filter array corresponds to the {@code pos}
3490      * argument of the target, and so on in sequence.
3491      * <p>
3492      * Null arguments in the array are treated as identity functions,
3493      * and the corresponding arguments left unchanged.
3494      * (If there are no non-null elements in the array, the original target is returned.)
3495      * Each filter is applied to the corresponding argument of the adapter.
3496      * <p>
3497      * If a filter {@code F} applies to the {@code N}th argument of
3498      * the target, then {@code F} must be a method handle which
3499      * takes exactly one argument.  The type of {@code F}'s sole argument
3500      * replaces the corresponding argument type of the target
3501      * in the resulting adapted method handle.
3502      * The return type of {@code F} must be identical to the corresponding
3503      * parameter type of the target.
3504      * <p>
3505      * It is an error if there are elements of {@code filters}
3506      * (null or not)
3507      * which do not correspond to argument positions in the target.
3508      * <p><b>Example:</b>
3509      * <blockquote><pre>{@code
3510 import static java.lang.invoke.MethodHandles.*;
3511 import static java.lang.invoke.MethodType.*;
3512 ...
3513 MethodHandle cat = lookup().findVirtual(String.class,
3514   "concat", methodType(String.class, String.class));
3515 MethodHandle upcase = lookup().findVirtual(String.class,
3516   "toUpperCase", methodType(String.class));
3517 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3518 MethodHandle f0 = filterArguments(cat, 0, upcase);
3519 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3520 MethodHandle f1 = filterArguments(cat, 1, upcase);
3521 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3522 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3523 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3524      * }</pre></blockquote>
3525      * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3526      * denotes the return type of both the {@code target} and resulting adapter.
3527      * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3528      * of the parameters and arguments that precede and follow the filter position
3529      * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3530      * values of the filtered parameters and arguments; they also represent the
3531      * return types of the {@code filter[i]} handles. The latter accept arguments
3532      * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3533      * the resulting adapter.
3534      * <blockquote><pre>{@code
3535      * T target(P... p, A[i]... a[i], B... b);
3536      * A[i] filter[i](V[i]);
3537      * T adapter(P... p, V[i]... v[i], B... b) {
3538      *   return target(p..., filter[i](v[i])..., b...);
3539      * }
3540      * }</pre></blockquote>
3541      * <p>
3542      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3543      * variable-arity method handle}, even if the original target method handle was.
3544      *
3545      * @param target the method handle to invoke after arguments are filtered
3546      * @param pos the position of the first argument to filter
3547      * @param filters method handles to call initially on filtered arguments
3548      * @return method handle which incorporates the specified argument filtering logic
3549      * @throws NullPointerException if the target is null
3550      *                              or if the {@code filters} array is null
3551      * @throws IllegalArgumentException if a non-null element of {@code filters}
3552      *          does not match a corresponding argument type of target as described above,
3553      *          or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3554      *          or if the resulting method handle's type would have
3555      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
3556      */
3557     public static
3558     MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3559         filterArgumentsCheckArity(target, pos, filters);
3560         MethodHandle adapter = target;
3561         int curPos = pos-1;  // pre-incremented
3562         for (MethodHandle filter : filters) {
3563             curPos += 1;
3564             if (filter == null)  continue;  // ignore null elements of filters
3565             adapter = filterArgument(adapter, curPos, filter);
3566         }
3567         return adapter;
3568     }
3569 
3570     /*non-public*/ static
3571     MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3572         filterArgumentChecks(target, pos, filter);
3573         MethodType targetType = target.type();
3574         MethodType filterType = filter.type();
3575         BoundMethodHandle result = target.rebind();
3576         Class<?> newParamType = filterType.parameterType(0);
3577         LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3578         MethodType newType = targetType.changeParameterType(pos, newParamType);
3579         result = result.copyWithExtendL(newType, lform, filter);
3580         return result;
3581     }
3582 
3583     private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3584         MethodType targetType = target.type();
3585         int maxPos = targetType.parameterCount();
3586         if (pos + filters.length > maxPos)
3587             throw newIllegalArgumentException("too many filters");
3588     }
3589 
3590     private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3591         MethodType targetType = target.type();
3592         MethodType filterType = filter.type();
3593         if (filterType.parameterCount() != 1
3594             || filterType.returnType() != targetType.parameterType(pos))
3595             throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3596     }
3597 
3598     /**
3599      * Adapts a target method handle by pre-processing
3600      * a sub-sequence of its arguments with a filter (another method handle).
3601      * The pre-processed arguments are replaced by the result (if any) of the
3602      * filter function.
3603      * The target is then called on the modified (usually shortened) argument list.
3604      * <p>
3605      * If the filter returns a value, the target must accept that value as
3606      * its argument in position {@code pos}, preceded and/or followed by
3607      * any arguments not passed to the filter.
3608      * If the filter returns void, the target must accept all arguments
3609      * not passed to the filter.
3610      * No arguments are reordered, and a result returned from the filter
3611      * replaces (in order) the whole subsequence of arguments originally
3612      * passed to the adapter.
3613      * <p>
3614      * The argument types (if any) of the filter
3615      * replace zero or one argument types of the target, at position {@code pos},
3616      * in the resulting adapted method handle.
3617      * The return type of the filter (if any) must be identical to the
3618      * argument type of the target at position {@code pos}, and that target argument
3619      * is supplied by the return value of the filter.
3620      * <p>
3621      * In all cases, {@code pos} must be greater than or equal to zero, and
3622      * {@code pos} must also be less than or equal to the target's arity.
3623      * <p><b>Example:</b>
3624      * <blockquote><pre>{@code
3625 import static java.lang.invoke.MethodHandles.*;
3626 import static java.lang.invoke.MethodType.*;
3627 ...
3628 MethodHandle deepToString = publicLookup()
3629   .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3630 
3631 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3632 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3633 
3634 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3635 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3636 
3637 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3638 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3639 assertEquals("[top, [up, down], strange]",
3640              (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3641 
3642 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3643 assertEquals("[top, [up, down], [strange]]",
3644              (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3645 
3646 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3647 assertEquals("[top, [[up, down, strange], charm], bottom]",
3648              (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3649      * }</pre></blockquote>
3650      * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3651      * represents the return type of the {@code target} and resulting adapter.
3652      * {@code V}/{@code v} stand for the return type and value of the
3653      * {@code filter}, which are also found in the signature and arguments of
3654      * the {@code target}, respectively, unless {@code V} is {@code void}.
3655      * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3656      * and values preceding and following the collection position, {@code pos},
3657      * in the {@code target}'s signature. They also turn up in the resulting
3658      * adapter's signature and arguments, where they surround
3659      * {@code B}/{@code b}, which represent the parameter types and arguments
3660      * to the {@code filter} (if any).
3661      * <blockquote><pre>{@code
3662      * T target(A...,V,C...);
3663      * V filter(B...);
3664      * T adapter(A... a,B... b,C... c) {
3665      *   V v = filter(b...);
3666      *   return target(a...,v,c...);
3667      * }
3668      * // and if the filter has no arguments:
3669      * T target2(A...,V,C...);
3670      * V filter2();
3671      * T adapter2(A... a,C... c) {
3672      *   V v = filter2();
3673      *   return target2(a...,v,c...);
3674      * }
3675      * // and if the filter has a void return:
3676      * T target3(A...,C...);
3677      * void filter3(B...);
3678      * T adapter3(A... a,B... b,C... c) {
3679      *   filter3(b...);
3680      *   return target3(a...,c...);
3681      * }
3682      * }</pre></blockquote>
3683      * <p>
3684      * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3685      * one which first "folds" the affected arguments, and then drops them, in separate
3686      * steps as follows:
3687      * <blockquote><pre>{@code
3688      * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3689      * mh = MethodHandles.foldArguments(mh, coll); //step 1
3690      * }</pre></blockquote>
3691      * If the target method handle consumes no arguments besides than the result
3692      * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3693      * is equivalent to {@code filterReturnValue(coll, mh)}.
3694      * If the filter method handle {@code coll} consumes one argument and produces
3695      * a non-void result, then {@code collectArguments(mh, N, coll)}
3696      * is equivalent to {@code filterArguments(mh, N, coll)}.
3697      * Other equivalences are possible but would require argument permutation.
3698      * <p>
3699      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3700      * variable-arity method handle}, even if the original target method handle was.
3701      *
3702      * @param target the method handle to invoke after filtering the subsequence of arguments
3703      * @param pos the position of the first adapter argument to pass to the filter,
3704      *            and/or the target argument which receives the result of the filter
3705      * @param filter method handle to call on the subsequence of arguments
3706      * @return method handle which incorporates the specified argument subsequence filtering logic
3707      * @throws NullPointerException if either argument is null
3708      * @throws IllegalArgumentException if the return type of {@code filter}
3709      *          is non-void and is not the same as the {@code pos} argument of the target,
3710      *          or if {@code pos} is not between 0 and the target's arity, inclusive,
3711      *          or if the resulting method handle's type would have
3712      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
3713      * @see MethodHandles#foldArguments
3714      * @see MethodHandles#filterArguments
3715      * @see MethodHandles#filterReturnValue
3716      */
3717     public static
3718     MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3719         MethodType newType = collectArgumentsChecks(target, pos, filter);
3720         MethodType collectorType = filter.type();
3721         BoundMethodHandle result = target.rebind();
3722         LambdaForm lform;
3723         if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3724             lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3725             if (lform != null) {
3726                 return result.copyWith(newType, lform);
3727             }
3728         }
3729         lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3730         return result.copyWithExtendL(newType, lform, filter);
3731     }
3732 
3733     private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3734         MethodType targetType = target.type();
3735         MethodType filterType = filter.type();
3736         Class<?> rtype = filterType.returnType();
3737         List<Class<?>> filterArgs = filterType.parameterList();
3738         if (rtype == void.class) {
3739             return targetType.insertParameterTypes(pos, filterArgs);
3740         }
3741         if (rtype != targetType.parameterType(pos)) {
3742             throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3743         }
3744         return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3745     }
3746 
3747     /**
3748      * Adapts a target method handle by post-processing
3749      * its return value (if any) with a filter (another method handle).
3750      * The result of the filter is returned from the adapter.
3751      * <p>
3752      * If the target returns a value, the filter must accept that value as
3753      * its only argument.
3754      * If the target returns void, the filter must accept no arguments.
3755      * <p>
3756      * The return type of the filter
3757      * replaces the return type of the target
3758      * in the resulting adapted method handle.
3759      * The argument type of the filter (if any) must be identical to the
3760      * return type of the target.
3761      * <p><b>Example:</b>
3762      * <blockquote><pre>{@code
3763 import static java.lang.invoke.MethodHandles.*;
3764 import static java.lang.invoke.MethodType.*;
3765 ...
3766 MethodHandle cat = lookup().findVirtual(String.class,
3767   "concat", methodType(String.class, String.class));
3768 MethodHandle length = lookup().findVirtual(String.class,
3769   "length", methodType(int.class));
3770 System.out.println((String) cat.invokeExact("x", "y")); // xy
3771 MethodHandle f0 = filterReturnValue(cat, length);
3772 System.out.println((int) f0.invokeExact("x", "y")); // 2
3773      * }</pre></blockquote>
3774      * <p>Here is pseudocode for the resulting adapter. In the code,
3775      * {@code T}/{@code t} represent the result type and value of the
3776      * {@code target}; {@code V}, the result type of the {@code filter}; and
3777      * {@code A}/{@code a}, the types and values of the parameters and arguments
3778      * of the {@code target} as well as the resulting adapter.
3779      * <blockquote><pre>{@code
3780      * T target(A...);
3781      * V filter(T);
3782      * V adapter(A... a) {
3783      *   T t = target(a...);
3784      *   return filter(t);
3785      * }
3786      * // and if the target has a void return:
3787      * void target2(A...);
3788      * V filter2();
3789      * V adapter2(A... a) {
3790      *   target2(a...);
3791      *   return filter2();
3792      * }
3793      * // and if the filter has a void return:
3794      * T target3(A...);
3795      * void filter3(V);
3796      * void adapter3(A... a) {
3797      *   T t = target3(a...);
3798      *   filter3(t);
3799      * }
3800      * }</pre></blockquote>
3801      * <p>
3802      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3803      * variable-arity method handle}, even if the original target method handle was.
3804      * @param target the method handle to invoke before filtering the return value
3805      * @param filter method handle to call on the return value
3806      * @return method handle which incorporates the specified return value filtering logic
3807      * @throws NullPointerException if either argument is null
3808      * @throws IllegalArgumentException if the argument list of {@code filter}
3809      *          does not match the return type of target as described above
3810      */
3811     public static
3812     MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
3813         MethodType targetType = target.type();
3814         MethodType filterType = filter.type();
3815         filterReturnValueChecks(targetType, filterType);
3816         BoundMethodHandle result = target.rebind();
3817         BasicType rtype = BasicType.basicType(filterType.returnType());
3818         LambdaForm lform = result.editor().filterReturnForm(rtype, false);
3819         MethodType newType = targetType.changeReturnType(filterType.returnType());
3820         result = result.copyWithExtendL(newType, lform, filter);
3821         return result;
3822     }
3823 
3824     private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
3825         Class<?> rtype = targetType.returnType();
3826         int filterValues = filterType.parameterCount();
3827         if (filterValues == 0
3828                 ? (rtype != void.class)
3829                 : (rtype != filterType.parameterType(0) || filterValues != 1))
3830             throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3831     }
3832 
3833     /**
3834      * Adapts a target method handle by pre-processing
3835      * some of its arguments, and then calling the target with
3836      * the result of the pre-processing, inserted into the original
3837      * sequence of arguments.
3838      * <p>
3839      * The pre-processing is performed by {@code combiner}, a second method handle.
3840      * Of the arguments passed to the adapter, the first {@code N} arguments
3841      * are copied to the combiner, which is then called.
3842      * (Here, {@code N} is defined as the parameter count of the combiner.)
3843      * After this, control passes to the target, with any result
3844      * from the combiner inserted before the original {@code N} incoming
3845      * arguments.
3846      * <p>
3847      * If the combiner returns a value, the first parameter type of the target
3848      * must be identical with the return type of the combiner, and the next
3849      * {@code N} parameter types of the target must exactly match the parameters
3850      * of the combiner.
3851      * <p>
3852      * If the combiner has a void return, no result will be inserted,
3853      * and the first {@code N} parameter types of the target
3854      * must exactly match the parameters of the combiner.
3855      * <p>
3856      * The resulting adapter is the same type as the target, except that the
3857      * first parameter type is dropped,
3858      * if it corresponds to the result of the combiner.
3859      * <p>
3860      * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
3861      * that either the combiner or the target does not wish to receive.
3862      * If some of the incoming arguments are destined only for the combiner,
3863      * consider using {@link MethodHandle#asCollector asCollector} instead, since those
3864      * arguments will not need to be live on the stack on entry to the
3865      * target.)
3866      * <p><b>Example:</b>
3867      * <blockquote><pre>{@code
3868 import static java.lang.invoke.MethodHandles.*;
3869 import static java.lang.invoke.MethodType.*;
3870 ...
3871 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
3872   "println", methodType(void.class, String.class))
3873     .bindTo(System.out);
3874 MethodHandle cat = lookup().findVirtual(String.class,
3875   "concat", methodType(String.class, String.class));
3876 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
3877 MethodHandle catTrace = foldArguments(cat, trace);
3878 // also prints "boo":
3879 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
3880      * }</pre></blockquote>
3881      * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3882      * represents the result type of the {@code target} and resulting adapter.
3883      * {@code V}/{@code v} represent the type and value of the parameter and argument
3884      * of {@code target} that precedes the folding position; {@code V} also is
3885      * the result type of the {@code combiner}. {@code A}/{@code a} denote the
3886      * types and values of the {@code N} parameters and arguments at the folding
3887      * position. {@code B}/{@code b} represent the types and values of the
3888      * {@code target} parameters and arguments that follow the folded parameters
3889      * and arguments.
3890      * <blockquote><pre>{@code
3891      * // there are N arguments in A...
3892      * T target(V, A[N]..., B...);
3893      * V combiner(A...);
3894      * T adapter(A... a, B... b) {
3895      *   V v = combiner(a...);
3896      *   return target(v, a..., b...);
3897      * }
3898      * // and if the combiner has a void return:
3899      * T target2(A[N]..., B...);
3900      * void combiner2(A...);
3901      * T adapter2(A... a, B... b) {
3902      *   combiner2(a...);
3903      *   return target2(a..., b...);
3904      * }
3905      * }</pre></blockquote>
3906      * <p>
3907      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3908      * variable-arity method handle}, even if the original target method handle was.
3909      * @param target the method handle to invoke after arguments are combined
3910      * @param combiner method handle to call initially on the incoming arguments
3911      * @return method handle which incorporates the specified argument folding logic
3912      * @throws NullPointerException if either argument is null
3913      * @throws IllegalArgumentException if {@code combiner}'s return type
3914      *          is non-void and not the same as the first argument type of
3915      *          the target, or if the initial {@code N} argument types
3916      *          of the target
3917      *          (skipping one matching the {@code combiner}'s return type)
3918      *          are not identical with the argument types of {@code combiner}
3919      */
3920     public static
3921     MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
3922         return foldArguments(target, 0, combiner);
3923     }
3924 
3925     private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
3926         int foldArgs   = combinerType.parameterCount();
3927         Class<?> rtype = combinerType.returnType();
3928         int foldVals = rtype == void.class ? 0 : 1;
3929         int afterInsertPos = foldPos + foldVals;
3930         boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
3931         if (ok) {
3932             for (int i = 0; i < foldArgs; i++) {
3933                 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
3934                     ok = false;
3935                     break;
3936                 }
3937             }
3938         }
3939         if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
3940             ok = false;
3941         if (!ok)
3942             throw misMatchedTypes("target and combiner types", targetType, combinerType);
3943         return rtype;
3944     }
3945 



























3946     /**
3947      * Makes a method handle which adapts a target method handle,
3948      * by guarding it with a test, a boolean-valued method handle.
3949      * If the guard fails, a fallback handle is called instead.
3950      * All three method handles must have the same corresponding
3951      * argument and return types, except that the return type
3952      * of the test must be boolean, and the test is allowed
3953      * to have fewer arguments than the other two method handles.
3954      * <p>
3955      * Here is pseudocode for the resulting adapter. In the code, {@code T}
3956      * represents the uniform result type of the three involved handles;
3957      * {@code A}/{@code a}, the types and values of the {@code target}
3958      * parameters and arguments that are consumed by the {@code test}; and
3959      * {@code B}/{@code b}, those types and values of the {@code target}
3960      * parameters and arguments that are not consumed by the {@code test}.
3961      * <blockquote><pre>{@code
3962      * boolean test(A...);
3963      * T target(A...,B...);
3964      * T fallback(A...,B...);
3965      * T adapter(A... a,B... b) {
3966      *   if (test(a...))
3967      *     return target(a..., b...);
3968      *   else
3969      *     return fallback(a..., b...);
3970      * }
3971      * }</pre></blockquote>
3972      * Note that the test arguments ({@code a...} in the pseudocode) cannot
3973      * be modified by execution of the test, and so are passed unchanged
3974      * from the caller to the target or fallback as appropriate.
3975      * @param test method handle used for test, must return boolean
3976      * @param target method handle to call if test passes
3977      * @param fallback method handle to call if test fails
3978      * @return method handle which incorporates the specified if/then/else logic
3979      * @throws NullPointerException if any argument is null
3980      * @throws IllegalArgumentException if {@code test} does not return boolean,
3981      *          or if all three method types do not match (with the return
3982      *          type of {@code test} changed to match that of the target).
3983      */
3984     public static
3985     MethodHandle guardWithTest(MethodHandle test,
3986                                MethodHandle target,
3987                                MethodHandle fallback) {
3988         MethodType gtype = test.type();
3989         MethodType ttype = target.type();
3990         MethodType ftype = fallback.type();
3991         if (!ttype.equals(ftype))
3992             throw misMatchedTypes("target and fallback types", ttype, ftype);
3993         if (gtype.returnType() != boolean.class)
3994             throw newIllegalArgumentException("guard type is not a predicate "+gtype);
3995         List<Class<?>> targs = ttype.parameterList();
3996         test = dropArgumentsToMatch(test, 0, targs, 0, true);
3997         if (test == null) {
3998             throw misMatchedTypes("target and test types", ttype, gtype);
3999         }
4000         return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4001     }
4002 
4003     static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4004         return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4005     }
4006 
4007     /**
4008      * Makes a method handle which adapts a target method handle,
4009      * by running it inside an exception handler.
4010      * If the target returns normally, the adapter returns that value.
4011      * If an exception matching the specified type is thrown, the fallback
4012      * handle is called instead on the exception, plus the original arguments.
4013      * <p>
4014      * The target and handler must have the same corresponding
4015      * argument and return types, except that handler may omit trailing arguments
4016      * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4017      * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4018      * <p>
4019      * Here is pseudocode for the resulting adapter. In the code, {@code T}
4020      * represents the return type of the {@code target} and {@code handler},
4021      * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4022      * the types and values of arguments to the resulting handle consumed by
4023      * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4024      * resulting handle discarded by {@code handler}.
4025      * <blockquote><pre>{@code
4026      * T target(A..., B...);
4027      * T handler(ExType, A...);
4028      * T adapter(A... a, B... b) {
4029      *   try {
4030      *     return target(a..., b...);
4031      *   } catch (ExType ex) {
4032      *     return handler(ex, a...);
4033      *   }
4034      * }
4035      * }</pre></blockquote>
4036      * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4037      * be modified by execution of the target, and so are passed unchanged
4038      * from the caller to the handler, if the handler is invoked.
4039      * <p>
4040      * The target and handler must return the same type, even if the handler
4041      * always throws.  (This might happen, for instance, because the handler
4042      * is simulating a {@code finally} clause).
4043      * To create such a throwing handler, compose the handler creation logic
4044      * with {@link #throwException throwException},
4045      * in order to create a method handle of the correct return type.
4046      * @param target method handle to call
4047      * @param exType the type of exception which the handler will catch
4048      * @param handler method handle to call if a matching exception is thrown
4049      * @return method handle which incorporates the specified try/catch logic
4050      * @throws NullPointerException if any argument is null
4051      * @throws IllegalArgumentException if {@code handler} does not accept
4052      *          the given exception type, or if the method handle types do
4053      *          not match in their return types and their
4054      *          corresponding parameters
4055      * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4056      */
4057     public static
4058     MethodHandle catchException(MethodHandle target,
4059                                 Class<? extends Throwable> exType,
4060                                 MethodHandle handler) {
4061         MethodType ttype = target.type();
4062         MethodType htype = handler.type();
4063         if (!Throwable.class.isAssignableFrom(exType))
4064             throw new ClassCastException(exType.getName());
4065         if (htype.parameterCount() < 1 ||
4066             !htype.parameterType(0).isAssignableFrom(exType))
4067             throw newIllegalArgumentException("handler does not accept exception type "+exType);
4068         if (htype.returnType() != ttype.returnType())
4069             throw misMatchedTypes("target and handler return types", ttype, htype);
4070         handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4071         if (handler == null) {
4072             throw misMatchedTypes("target and handler types", ttype, htype);
4073         }
4074         return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4075     }
4076 
4077     /**
4078      * Produces a method handle which will throw exceptions of the given {@code exType}.
4079      * The method handle will accept a single argument of {@code exType},
4080      * and immediately throw it as an exception.
4081      * The method type will nominally specify a return of {@code returnType}.
4082      * The return type may be anything convenient:  It doesn't matter to the
4083      * method handle's behavior, since it will never return normally.
4084      * @param returnType the return type of the desired method handle
4085      * @param exType the parameter type of the desired method handle
4086      * @return method handle which can throw the given exceptions
4087      * @throws NullPointerException if either argument is null
4088      */
4089     public static
4090     MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4091         if (!Throwable.class.isAssignableFrom(exType))
4092             throw new ClassCastException(exType.getName());
4093         return MethodHandleImpl.throwException(methodType(returnType, exType));
4094     }
4095 
4096     /**
4097      * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4098      * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4099      * delivers the loop's result, which is the return value of the resulting handle.
4100      * <p>
4101      * Intuitively, every loop is formed by one or more "clauses", each specifying a local iteration value and/or a loop
4102      * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4103      * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4104      * terms of method handles, each clause will determine four actions:<ul>
4105      * <li>Before the loop executes, the initialization of an iteration variable or loop invariant local.
4106      * <li>When a clause executes, an update step for the iteration variable.
4107      * <li>When a clause executes, a predicate execution to test for loop exit.
4108      * <li>If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4109      * </ul>
4110      * <p>
4111      * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4112      * this case. See below for a detailed description.
4113      * <p>
4114      * Each clause function, with the exception of clause initializers, is able to observe the entire loop state,
4115      * because it will be passed <em>all</em> current iteration variable values, as well as all incoming loop
4116      * parameters. Most clause functions will not need all of this information, but they will be formally connected as
4117      * if by {@link #dropArguments}.
4118      * <p>
4119      * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4120      * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4121      * corresponds to a place where {@link IllegalArgumentException} may be thrown if the required constraint is not met
4122      * by the inputs to the loop combinator. The term "effectively identical", applied to parameter type lists, means
4123      * that they must be identical, or else one list must be a proper prefix of the other.
4124      * <p>
4125      * <em>Step 0: Determine clause structure.</em><ol type="a">
4126      * <li>The clause array (of type {@code MethodHandle[][]} must be non-{@code null} and contain at least one element.
4127      * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4128      * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4129      * four. Padding takes place by appending elements to the array.
4130      * <li>Clauses with all {@code null}s are disregarded.
4131      * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4132      * </ol>
4133      * <p>
4134      * <em>Step 1A: Determine iteration variables.</em><ol type="a">
4135      * <li>Examine init and step function return types, pairwise, to determine each clause's iteration variable type.
4136      * <li>If both functions are omitted, use {@code void}; else if one is omitted, use the other's return type; else
4137      * use the common return type (they must be identical).
4138      * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4139      * <li>This list of types is called the "common prefix".
4140      * </ol>
4141      * <p>
4142      * <em>Step 1B: Determine loop parameters.</em><ul>
4143      * <li><b>If at least one init function is given,</b><ol type="a">
4144      *   <li>Examine init function parameter lists.
4145      *   <li>Omitted init functions are deemed to have {@code null} parameter lists.
4146      *   <li>All init function parameter lists must be effectively identical.
4147      *   <li>The longest parameter list (which is necessarily unique) is called the "common suffix".
4148      * </ol>
4149      * <li><b>If no init function is given,</b><ol type="a">
4150      *   <li>Examine the suffixes of the step, pred, and fini parameter lists, after removing the "common prefix".
4151      *   <li>The longest of these suffixes is taken as the "common suffix".
4152      * </ol></ul>
4153      * <p>
4154      * <em>Step 1C: Determine loop return type.</em><ol type="a">
4155      * <li>Examine fini function return types, disregarding omitted fini functions.
4156      * <li>If there are no fini functions, use {@code void} as the loop return type.
4157      * <li>Otherwise, use the common return type of the fini functions; they must all be identical.
4158      * </ol>
4159      * <p>
4160      * <em>Step 1D: Check other types.</em><ol type="a">
4161      * <li>There must be at least one non-omitted pred function.
4162      * <li>Every non-omitted pred function must have a {@code boolean} return type.
4163      * </ol>
4164      * <p>
4165      * <em>Step 2: Determine parameter lists.</em><ol type="a">
4166      * <li>The parameter list for the resulting loop handle will be the "common suffix".
4167      * <li>The parameter list for init functions will be adjusted to the "common suffix". (Note that their parameter
4168      * lists are already effectively identical to the common suffix.)
4169      * <li>The parameter list for non-init (step, pred, and fini) functions will be adjusted to the common prefix
4170      * followed by the common suffix, called the "common parameter sequence".
4171      * <li>Every non-init, non-omitted function parameter list must be effectively identical to the common parameter
4172      * sequence.
4173      * </ol>
4174      * <p>
4175      * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4176      * <li>If an init function is omitted, use a {@linkplain #constant constant function} of the appropriate
4177      * {@code null}/zero/{@code false}/{@code void} type. (For this purpose, a constant {@code void} is simply a
4178      * function which does nothing and returns {@code void}; it can be obtained from another constant function by
4179      * {@linkplain MethodHandle#asType type conversion}.)
4180      * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4181      * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4182      * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4183      * <li>If a pred function is omitted, the corresponding fini function must also be omitted.
4184      * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4185      * as this clause is concerned.)
4186      * <li>If a fini function is omitted, use a constant {@code null}/zero/{@code false}/{@code void} function of the
4187      * loop return type.
4188      * </ol>
4189      * <p>
4190      * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4191      * <li>At this point, every init function parameter list is effectively identical to the common suffix, but some
4192      * lists may be shorter. For every init function with a short parameter list, pad out the end of the list by
4193      * {@linkplain #dropArguments dropping arguments}.
4194      * <li>At this point, every non-init function parameter list is effectively identical to the common parameter
4195      * sequence, but some lists may be shorter. For every non-init function with a short parameter list, pad out the end
4196      * of the list by {@linkplain #dropArguments dropping arguments}.
4197      * </ol>
4198      * <p>
4199      * <em>Final observations.</em><ol type="a">
4200      * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4201      * <li>All init functions have a common parameter type list, which the final loop handle will also have.
4202      * <li>All fini functions have a common return type, which the final loop handle will also have.
4203      * <li>All non-init functions have a common parameter type list, which is the common parameter sequence, of
4204      * (non-{@code void}) iteration variables followed by loop parameters.
4205      * <li>Each pair of init and step functions agrees in their return types.
4206      * <li>Each non-init function will be able to observe the current values of all iteration variables, by means of the
4207      * common prefix.
4208      * </ol>
4209      * <p>
4210      * <em>Loop execution.</em><ol type="a">
4211      * <li>When the loop is called, the loop input values are saved in locals, to be passed (as the common suffix) to
4212      * every clause function. These locals are loop invariant.
4213      * <li>Each init function is executed in clause order (passing the common suffix) and the non-{@code void} values
4214      * are saved (as the common prefix) into locals. These locals are loop varying (unless their steps are identity
4215      * functions, as noted above).
4216      * <li>All function executions (except init functions) will be passed the common parameter sequence, consisting of
4217      * the non-{@code void} iteration values (in clause order) and then the loop inputs (in argument order).
4218      * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4219      * returns {@code false}.
4220      * <li>The non-{@code void} result from a step function call is used to update the corresponding loop variable. The
4221      * updated value is immediately visible to all subsequent function calls.
4222      * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4223      * is returned from the loop as a whole.
4224      * </ol>
4225      * <p>
4226      * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the types / values
4227      * of loop variables; {@code A}/{@code a}, those of arguments passed to the resulting loop; and {@code R}, the
4228      * result types of finalizers as well as of the resulting loop.
4229      * <blockquote><pre>{@code
4230      * V... init...(A...);
4231      * boolean pred...(V..., A...);
4232      * V... step...(V..., A...);
4233      * R fini...(V..., A...);
4234      * R loop(A... a) {
4235      *   V... v... = init...(a...);
4236      *   for (;;) {
4237      *     for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4238      *       v = s(v..., a...);
4239      *       if (!p(v..., a...)) {
4240      *         return f(v..., a...);
4241      *       }
4242      *     }
4243      *   }
4244      * }
4245      * }</pre></blockquote>
4246      * <p>
4247      * @apiNote Example:
4248      * <blockquote><pre>{@code
4249      * // iterative implementation of the factorial function as a loop handle
4250      * static int one(int k) { return 1; }
4251      * static int inc(int i, int acc, int k) { return i + 1; }
4252      * static int mult(int i, int acc, int k) { return i * acc; }
4253      * static boolean pred(int i, int acc, int k) { return i < k; }
4254      * static int fin(int i, int acc, int k) { return acc; }
4255      * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4256      * // null initializer for counter, should initialize to 0
4257      * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4258      * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4259      * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4260      * assertEquals(120, loop.invoke(5));
4261      * }</pre></blockquote>
4262      *
4263      * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4264      *
4265      * @return a method handle embodying the looping behavior as defined by the arguments.
4266      *
4267      * @throws IllegalArgumentException in case any of the constraints described above is violated.
4268      *
4269      * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4270      * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4271      * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4272      * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4273      * @since 9
4274      */
4275     public static MethodHandle loop(MethodHandle[]... clauses) {
4276         // Step 0: determine clause structure.
4277         checkLoop0(clauses);
4278 
4279         List<MethodHandle> init = new ArrayList<>();
4280         List<MethodHandle> step = new ArrayList<>();
4281         List<MethodHandle> pred = new ArrayList<>();
4282         List<MethodHandle> fini = new ArrayList<>();
4283 
4284         Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4285             init.add(clause[0]); // all clauses have at least length 1
4286             step.add(clause.length <= 1 ? null : clause[1]);
4287             pred.add(clause.length <= 2 ? null : clause[2]);
4288             fini.add(clause.length <= 3 ? null : clause[3]);
4289         });
4290 
4291         assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4292         final int nclauses = init.size();
4293 
4294         // Step 1A: determine iteration variables.
4295         final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4296         for (int i = 0; i < nclauses; ++i) {
4297             MethodHandle in = init.get(i);
4298             MethodHandle st = step.get(i);
4299             if (in == null && st == null) {
4300                 iterationVariableTypes.add(void.class);
4301             } else if (in != null && st != null) {
4302                 checkLoop1a(i, in, st);
4303                 iterationVariableTypes.add(in.type().returnType());
4304             } else {
4305                 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4306             }
4307         }
4308         final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4309                 collect(Collectors.toList());
4310 
4311         // Step 1B: determine loop parameters.
4312         final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4313         checkLoop1b(init, commonSuffix);
4314 
4315         // Step 1C: determine loop return type.
4316         // Step 1D: check other types.
4317         final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4318                 map(MethodType::returnType).findFirst().orElse(void.class);
4319         checkLoop1cd(pred, fini, loopReturnType);
4320 
4321         // Step 2: determine parameter lists.
4322         final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4323         commonParameterSequence.addAll(commonSuffix);
4324         checkLoop2(step, pred, fini, commonParameterSequence);
4325 
4326         // Step 3: fill in omitted functions.
4327         for (int i = 0; i < nclauses; ++i) {
4328             Class<?> t = iterationVariableTypes.get(i);
4329             if (init.get(i) == null) {
4330                 init.set(i, empty(methodType(t, commonSuffix)));
4331             }
4332             if (step.get(i) == null) {
4333                 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4334             }
4335             if (pred.get(i) == null) {
4336                 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4337             }
4338             if (fini.get(i) == null) {
4339                 fini.set(i, empty(methodType(t, commonParameterSequence)));
4340             }
4341         }
4342 
4343         // Step 4: fill in missing parameter types.
4344         List<MethodHandle> finit = fillParameterTypes(init, commonSuffix);
4345         List<MethodHandle> fstep = fillParameterTypes(step, commonParameterSequence);
4346         List<MethodHandle> fpred = fillParameterTypes(pred, commonParameterSequence);
4347         List<MethodHandle> ffini = fillParameterTypes(fini, commonParameterSequence);
4348 
4349         assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4350                 allMatch(pl -> pl.equals(commonSuffix));
4351         assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4352                 allMatch(pl -> pl.equals(commonParameterSequence));
4353 
4354         return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4355     }
4356 
4357     private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4358         return hs.stream().map(h -> {
4359             int pc = h.type().parameterCount();
4360             int tpsize = targetParams.size();
4361             return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4362         }).collect(Collectors.toList());
4363     }
4364 
4365     /**
4366      * Constructs a {@code while} loop from an initializer, a body, and a predicate. This is a convenience wrapper for
4367      * the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4368      * <p>
4369      * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
4370      * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
4371      * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
4372      * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
4373      * generic loop combinator}.
4374      * <p>
4375      * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4376      * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4377      * passed to the loop.
4378      * <blockquote><pre>{@code
4379      * V init(A);
4380      * boolean pred(V, A);
4381      * V body(V, A);
4382      * V whileLoop(A a) {
4383      *   V v = init(a);
4384      *   while (pred(v, a)) {
4385      *     v = body(v, a);
4386      *   }
4387      *   return v;
4388      * }
4389      * }</pre></blockquote>
4390      * <p>
4391      * @apiNote Example:
4392      * <blockquote><pre>{@code
4393      * // implement the zip function for lists as a loop handle
4394      * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
4395      * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
4396      * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
4397      *   zip.add(a.next());
4398      *   zip.add(b.next());
4399      *   return zip;
4400      * }
4401      * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
4402      * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
4403      * List<String> a = Arrays.asList("a", "b", "c", "d");
4404      * List<String> b = Arrays.asList("e", "f", "g", "h");
4405      * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
4406      * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
4407      * }</pre></blockquote>
4408      *
4409      * <p>
4410      * @implSpec The implementation of this method is equivalent to:
4411      * <blockquote><pre>{@code
4412      * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4413      *     MethodHandle[]
4414      *         checkExit = {null, null, pred, identity(init.type().returnType())},
4415      *         varBody = {init, body};
4416      *     return loop(checkExit, varBody);
4417      * }
4418      * }</pre></blockquote>
4419      *
4420      * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
4421      *             result type. Passing {@code null} or a {@code void} init function will make the loop's result type
4422      *             {@code void}.
4423      * @param pred condition for the loop, which may not be {@code null}.
4424      * @param body body of the loop, which may not be {@code null}.
4425      *
4426      * @return the value of the loop variable as the loop terminates.
4427      * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4428      *
4429      * @see MethodHandles#loop(MethodHandle[][])
4430      * @since 9
4431      */
4432     public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4433         MethodHandle fin = init == null || init.type().returnType() == void.class ? zero(void.class) :
4434                 identity(init.type().returnType());
4435         MethodHandle[] checkExit = {null, null, pred, fin};
4436         MethodHandle[] varBody = {init, body};
4437         return loop(checkExit, varBody);
4438     }
4439 
4440     /**
4441      * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. This is a convenience wrapper
4442      * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4443      * <p>
4444      * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
4445      * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
4446      * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
4447      * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
4448      * generic loop combinator}.
4449      * <p>
4450      * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4451      * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4452      * passed to the loop.
4453      * <blockquote><pre>{@code
4454      * V init(A);
4455      * boolean pred(V, A);
4456      * V body(V, A);
4457      * V doWhileLoop(A a) {
4458      *   V v = init(a);
4459      *   do {
4460      *     v = body(v, a);
4461      *   } while (pred(v, a));
4462      *   return v;
4463      * }
4464      * }</pre></blockquote>
4465      * <p>
4466      * @apiNote Example:
4467      * <blockquote><pre>{@code
4468      * // int i = 0; while (i < limit) { ++i; } return i; => limit
4469      * static int zero(int limit) { return 0; }
4470      * static int step(int i, int limit) { return i + 1; }
4471      * static boolean pred(int i, int limit) { return i < limit; }
4472      * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
4473      * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
4474      * assertEquals(23, loop.invoke(23));
4475      * }</pre></blockquote>
4476      *
4477      * <p>
4478      * @implSpec The implementation of this method is equivalent to:
4479      * <blockquote><pre>{@code
4480      * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4481      *     MethodHandle[] clause = { init, body, pred, identity(init.type().returnType()) };
4482      *     return loop(clause);
4483      * }
4484      * }</pre></blockquote>
4485      *
4486      *
4487      * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
4488      *             result type. Passing {@code null} or a {@code void} init function will make the loop's result type
4489      *             {@code void}.
4490      * @param pred condition for the loop, which may not be {@code null}.
4491      * @param body body of the loop, which may not be {@code null}.
4492      *
4493      * @return the value of the loop variable as the loop terminates.
4494      * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4495      *
4496      * @see MethodHandles#loop(MethodHandle[][])
4497      * @since 9
4498      */
4499     public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4500         MethodHandle fin = init == null || init.type().returnType() == void.class ? zero(void.class) :
4501                 identity(init.type().returnType());
4502         MethodHandle[] clause = {init, body, pred, fin};
4503         return loop(clause);
4504     }
4505 
4506     /**
4507      * Constructs a loop that runs a given number of iterations. The loop counter is an {@code int} initialized from the
4508      * {@code iterations} handle evaluation result. The counter is passed to the {@code body} function, so that must
4509      * accept an initial {@code int} argument. The result of the loop execution is the final value of the additional
4510      * local state. This is a convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop
4511      * combinator}.
4512      * <p>
4513      * The result type and parameter type list of {@code init} determine those of the resulting handle. The {@code
4514      * iterations} handle must accept the same parameter types as {@code init} but return an {@code int}. The {@code
4515      * body} handle must accept the same parameter types as well, preceded by an {@code int} parameter for the counter,
4516      * and a parameter of the same type as {@code init}'s result. These constraints follow directly from those described
4517      * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4518      * <p>
4519      * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4520      * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4521      * passed to the loop.
4522      * <blockquote><pre>{@code
4523      * int iterations(A);
4524      * V init(A);
4525      * V body(int, V, A);
4526      * V countedLoop(A a) {
4527      *   int end = iterations(a);
4528      *   V v = init(a);
4529      *   for (int i = 0; i < end; ++i) {
4530      *     v = body(i, v, a);
4531      *   }
4532      *   return v;
4533      * }
4534      * }</pre></blockquote>
4535      * <p>
4536      * @apiNote Example:
4537      * <blockquote><pre>{@code
4538      * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
4539      * // => a variation on a well known theme
4540      * static String start(String arg) { return arg; }
4541      * static String step(int counter, String v, String arg) { return "na " + v; }
4542      * // assume MH_start and MH_step are handles to the two methods above
4543      * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
4544      * MethodHandle loop = MethodHandles.countedLoop(fit13, MH_start, MH_step);
4545      * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
4546      * }</pre></blockquote>
4547      *
4548      * <p>
4549      * @implSpec The implementation of this method is equivalent to:
4550      * <blockquote><pre>{@code
4551      * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
4552      *     return countedLoop(null, iterations, init, body);  // null => constant zero
4553      * }
4554      * }</pre></blockquote>
4555      *
4556      * @param iterations a handle to return the number of iterations this loop should run.
4557      * @param init initializer for additional loop state. This determines the loop's result type.
4558      *             Passing {@code null} or a {@code void} init function will make the loop's result type
4559      *             {@code void}.
4560      * @param body the body of the loop, which must not be {@code null}.
4561      *             It must accept an initial {@code int} parameter (for the counter), and then any
4562      *             additional loop-local variable plus loop parameters.
4563      *
4564      * @return a method handle representing the loop.
4565      * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4566      *
4567      * @since 9
4568      */
4569     public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
4570         return countedLoop(null, iterations, init, body);
4571     }
4572 
4573     /**
4574      * Constructs a loop that counts over a range of numbers. The loop counter is an {@code int} that will be
4575      * initialized to the {@code int} value returned from the evaluation of the {@code start} handle and run to the
4576      * value returned from {@code end} (exclusively) with a step width of 1. The counter value is passed to the {@code
4577      * body} function in each iteration; it has to accept an initial {@code int} parameter
4578      * for that. The result of the loop execution is the final value of the additional local state
4579      * obtained by running {@code init}.
4580      * This is a
4581      * convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4582      * <p>
4583      * The constraints for the {@code init} and {@code body} handles are the same as for {@link
4584      * #countedLoop(MethodHandle, MethodHandle, MethodHandle)}. Additionally, the {@code start} and {@code end} handles
4585      * must return an {@code int} and accept the same parameters as {@code init}.
4586      * <p>
4587      * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4588      * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4589      * passed to the loop.
4590      * <blockquote><pre>{@code
4591      * int start(A);
4592      * int end(A);
4593      * V init(A);
4594      * V body(int, V, A);
4595      * V countedLoop(A a) {
4596      *   int s = start(a);
4597      *   int e = end(a);
4598      *   V v = init(a);
4599      *   for (int i = s; i < e; ++i) {
4600      *     v = body(i, v, a);
4601      *   }
4602      *   return v;
4603      * }
4604      * }</pre></blockquote>
4605      *
4606      * <p>
4607      * @implSpec The implementation of this method is equivalent to:
4608      * <blockquote><pre>{@code
4609      * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
4610      *     MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
4611      *     // assume MH_increment and MH_lessThan are handles to x+1 and x<y of type int,
4612      *     // assume MH_decrement is a handle to x-1 of type int
4613      *     MethodHandle[]
4614      *         indexVar = {start, MH_increment}, // i = start; i = i+1
4615      *         loopLimit = {end, null,
4616      *                       filterArgument(MH_lessThan, 0, MH_decrement), returnVar}, // i-1<end
4617      *         bodyClause = {init,
4618      *                       filterArgument(dropArguments(body, 1, int.class), 0, MH_decrement}; // v = body(i-1, v)
4619      *     return loop(indexVar, loopLimit, bodyClause);
4620      * }
4621      * }</pre></blockquote>
4622      *
4623      * @param start a handle to return the start value of the loop counter.
4624      *              If it is {@code null}, a constant zero is assumed.
4625      * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to {@code end-1}).
4626      * @param init initializer for additional loop state. This determines the loop's result type.
4627      *             Passing {@code null} or a {@code void} init function will make the loop's result type
4628      *             {@code void}.
4629      * @param body the body of the loop, which must not be {@code null}.
4630      *             It must accept an initial {@code int} parameter (for the counter), and then any
4631      *             additional loop-local variable plus loop parameters.
4632      *
4633      * @return a method handle representing the loop.
4634      * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4635      *
4636      * @since 9
4637      */
4638     public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
4639         Class<?> resultType;
4640         MethodHandle actualInit;
4641         if (init == null) {
4642             resultType = body == null ? void.class : body.type().returnType();
4643             actualInit = empty(methodType(resultType));
4644         } else {
4645             resultType = init.type().returnType();
4646             actualInit = init;
4647         }
4648         MethodHandle defaultResultHandle = resultType == void.class ? zero(void.class) : identity(resultType);
4649         MethodHandle actualBody = body == null ? dropArguments(defaultResultHandle, 0, int.class) : body;
4650         MethodHandle returnVar = dropArguments(defaultResultHandle, 0, int.class, int.class);
4651         MethodHandle actualEnd = end == null ? constant(int.class, 0) : end;
4652         MethodHandle decr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_decrementCounter);
4653         MethodHandle[] indexVar = {start, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep)};
4654         MethodHandle[] loopLimit = {actualEnd, null,
4655                 filterArgument(MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred), 0, decr),
4656                 returnVar};
4657         MethodHandle[] bodyClause = {actualInit, filterArgument(dropArguments(actualBody, 1, int.class), 0, decr)};
4658         return loop(indexVar, loopLimit, bodyClause);
4659     }
4660 
4661     /**
4662      * Constructs a loop that ranges over the elements produced by an {@code Iterator<T>}.
4663      * The iterator will be produced by the evaluation of the {@code iterator} handle.
4664      * This handle must have {@link java.util.Iterator} as its return type.
4665      * If this handle is passed as {@code null} the method {@link Iterable#iterator} will be used instead,
4666      * and will be applied to a leading argument of the loop handle.
4667      * Each value produced by the iterator is passed to the {@code body}, which must accept an initial {@code T} parameter.
4668      * The result of the loop execution is the final value of the additional local state
4669      * obtained by running {@code init}.
4670      * <p>
4671      * This is a convenience wrapper for the
4672      * {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}, and the constraints imposed on the {@code body}
4673      * handle follow directly from those described for the latter.
4674      * <p>
4675      * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4676      * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
4677      * structure the loop iterates over, and {@code A}/{@code a}, that of the argument passed to the loop.
4678      * <blockquote><pre>{@code
4679      * Iterator<T> iterator(A);  // defaults to Iterable::iterator
4680      * V init(A);
4681      * V body(T,V,A);
4682      * V iteratedLoop(A a) {
4683      *   Iterator<T> it = iterator(a);
4684      *   V v = init(a);
4685      *   for (T t : it) {
4686      *     v = body(t, v, a);
4687      *   }
4688      *   return v;
4689      * }
4690      * }</pre></blockquote>
4691      * <p>
4692      * The type {@code T} may be either a primitive or reference.
4693      * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type
4694      * {@code Iterator}, the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body}
4695      * to {@code Object} as if by the {@link MethodHandle#asType asType} conversion method.
4696      * Therefore, if an iterator of the wrong type appears as the loop is executed,
4697      * runtime exceptions may occur as the result of dynamic conversions performed by {@code asType}.
4698      * <p>
4699      * @apiNote Example:
4700      * <blockquote><pre>{@code
4701      * // reverse a list
4702      * static List<String> reverseStep(String e, List<String> r, List<String> l) {
4703      *   r.add(0, e);
4704      *   return r;
4705      * }
4706      * static List<String> newArrayList(List<String> l) { return new ArrayList<>(); }
4707      * // assume MH_reverseStep, MH_newArrayList are handles to the above methods
4708      * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
4709      * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
4710      * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
4711      * assertEquals(reversedList, (List<String>) loop.invoke(list));
4712      * }</pre></blockquote>
4713      * <p>
4714      * @implSpec The implementation of this method is equivalent to (excluding error handling):
4715      * <blockquote><pre>{@code
4716      * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
4717      *     // assume MH_next and MH_hasNext are handles to methods of Iterator
4718      *     Class<?> itype = iterator.type().returnType();
4719      *     Class<?> ttype = body.type().parameterType(0);
4720      *     MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, itype);
4721      *     MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
4722      *     MethodHandle[]
4723      *         iterVar = {iterator, null, MH_hasNext, returnVar}, // it = iterator(); while (it.hasNext)
4724      *         bodyClause = {init, filterArgument(body, 0, nextVal)};  // v = body(t, v, a);
4725      *     return loop(iterVar, bodyClause);
4726      * }
4727      * }</pre></blockquote>
4728      *
4729      * @param iterator a handle to return the iterator to start the loop.
4730      *             The handle must have {@link java.util.Iterator} as its return type.
4731      *             Passing {@code null} will make the loop call {@link Iterable#iterator()} on the first
4732      *             incoming value.
4733      * @param init initializer for additional loop state. This determines the loop's result type.
4734      *             Passing {@code null} or a {@code void} init function will make the loop's result type
4735      *             {@code void}.
4736      * @param body the body of the loop, which must not be {@code null}.
4737      *             It must accept an initial {@code T} parameter (for the iterated values), and then any
4738      *             additional loop-local variable plus loop parameters.
4739      *
4740      * @return a method handle embodying the iteration loop functionality.
4741      * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4742      *
4743      * @since 9
4744      */
4745     public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
4746         checkIteratedLoop(iterator, body);
4747         Class<?> resultType = init == null ?
4748                 body == null ? void.class : body.type().returnType() :
4749                 init.type().returnType();
4750         boolean voidResult = resultType == void.class;
4751 
4752         MethodHandle initIterator;
4753         if (iterator == null) {
4754             MethodHandle initit = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
4755             initIterator = initit.asType(initit.type().changeParameterType(0,
4756                     body.type().parameterType(voidResult ? 1 : 2)));
4757         } else {
4758             initIterator = iterator.asType(iterator.type().changeReturnType(Iterator.class));
4759         }
4760 
4761         Class<?> ttype = body.type().parameterType(0);
4762 
4763         MethodHandle returnVar =
4764                 dropArguments(voidResult ? zero(void.class) : identity(resultType), 0, Iterator.class);
4765         MethodHandle initnx = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
4766         MethodHandle nextVal = initnx.asType(initnx.type().changeReturnType(ttype));
4767 
4768         MethodHandle[] iterVar = {initIterator, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred),
4769                 returnVar};
4770         MethodHandle[] bodyClause = {init, filterArgument(body, 0, nextVal)};
4771 
4772         return loop(iterVar, bodyClause);
4773     }
4774 
4775     /**
4776      * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
4777      * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
4778      * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
4779      * exception will be rethrown, unless {@code cleanup} handle throws an exception first.  The
4780      * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
4781      * {@code try-finally} handle.
4782      * <p>
4783      * The {@code cleanup} handle will be passed one or two additional leading arguments.
4784      * The first is the exception thrown during the
4785      * execution of the {@code target} handle, or {@code null} if no exception was thrown.
4786      * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
4787      * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
4788      * The second argument is not present if the {@code target} handle has a {@code void} return type.
4789      * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
4790      * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
4791      * <p>
4792      * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
4793      * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
4794      * two extra leading parameters:<ul>
4795      * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
4796      * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
4797      * the result from the execution of the {@code target} handle.
4798      * This parameter is not present if the {@code target} returns {@code void}.
4799      * </ul>
4800      * <p>
4801      * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
4802      * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
4803      * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
4804      * the cleanup.
4805      * <blockquote><pre>{@code
4806      * V target(A..., B...);
4807      * V cleanup(Throwable, V, A...);
4808      * V adapter(A... a, B... b) {
4809      *   V result = (zero value for V);
4810      *   Throwable throwable = null;
4811      *   try {
4812      *     result = target(a..., b...);
4813      *   } catch (Throwable t) {
4814      *     throwable = t;
4815      *     throw t;
4816      *   } finally {
4817      *     result = cleanup(throwable, result, a...);
4818      *   }
4819      *   return result;
4820      * }
4821      * }</pre></blockquote>
4822      * <p>
4823      * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4824      * be modified by execution of the target, and so are passed unchanged
4825      * from the caller to the cleanup, if it is invoked.
4826      * <p>
4827      * The target and cleanup must return the same type, even if the cleanup
4828      * always throws.
4829      * To create such a throwing cleanup, compose the cleanup logic
4830      * with {@link #throwException throwException},
4831      * in order to create a method handle of the correct return type.
4832      * <p>
4833      * Note that {@code tryFinally} never converts exceptions into normal returns.
4834      * In rare cases where exceptions must be converted in that way, first wrap
4835      * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
4836      * to capture an outgoing exception, and then wrap with {@code tryFinally}.
4837      *
4838      * @param target the handle whose execution is to be wrapped in a {@code try} block.
4839      * @param cleanup the handle that is invoked in the finally block.
4840      *
4841      * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
4842      * @throws NullPointerException if any argument is null
4843      * @throws IllegalArgumentException if {@code cleanup} does not accept
4844      *          the required leading arguments, or if the method handle types do
4845      *          not match in their return types and their
4846      *          corresponding trailing parameters
4847      *
4848      * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
4849      * @since 9
4850      */
4851     public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
4852         List<Class<?>> targetParamTypes = target.type().parameterList();
4853         List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
4854         Class<?> rtype = target.type().returnType();
4855 
4856         checkTryFinally(target, cleanup);
4857 
4858         // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
4859         // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
4860         // target parameter list.
4861         cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
4862 
4863         return MethodHandleImpl.makeTryFinally(target, cleanup, rtype, targetParamTypes);
4864     }
4865 
4866     /**
4867      * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4868      * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4869      * before the folded arguments.
4870      * <p>
4871      * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4872      * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4873      * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4874      * 0.
4875      * <p>
4876      * @apiNote Example:
4877      * <blockquote><pre>{@code
4878     import static java.lang.invoke.MethodHandles.*;
4879     import static java.lang.invoke.MethodType.*;
4880     ...
4881     MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4882     "println", methodType(void.class, String.class))
4883     .bindTo(System.out);
4884     MethodHandle cat = lookup().findVirtual(String.class,
4885     "concat", methodType(String.class, String.class));
4886     assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4887     MethodHandle catTrace = foldArguments(cat, 1, trace);
4888     // also prints "jum":
4889     assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4890      * }</pre></blockquote>
4891      * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4892      * represents the result type of the {@code target} and resulting adapter.
4893      * {@code V}/{@code v} represent the type and value of the parameter and argument
4894      * of {@code target} that precedes the folding position; {@code V} also is
4895      * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4896      * types and values of the {@code N} parameters and arguments at the folding
4897      * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4898      * and values of the {@code target} parameters and arguments that precede and
4899      * follow the folded parameters and arguments starting at {@code pos},
4900      * respectively.
4901      * <blockquote><pre>{@code
4902      * // there are N arguments in A...
4903      * T target(Z..., V, A[N]..., B...);
4904      * V combiner(A...);
4905      * T adapter(Z... z, A... a, B... b) {
4906      *   V v = combiner(a...);
4907      *   return target(z..., v, a..., b...);
4908      * }
4909      * // and if the combiner has a void return:
4910      * T target2(Z..., A[N]..., B...);
4911      * void combiner2(A...);
4912      * T adapter2(Z... z, A... a, B... b) {
4913      *   combiner2(a...);
4914      *   return target2(z..., a..., b...);
4915      * }
4916      * }</pre></blockquote>
4917      * <p>
4918      * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4919      * variable-arity method handle}, even if the original target method handle was.
4920      *
4921      * @param target the method handle to invoke after arguments are combined
4922      * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4923      *            0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4924      * @param combiner method handle to call initially on the incoming arguments
4925      * @return method handle which incorporates the specified argument folding logic
4926      * @throws NullPointerException if either argument is null
4927      * @throws IllegalArgumentException if {@code combiner}'s return type
4928      *          is non-void and not the same as the argument type at position {@code pos} of
4929      *          the target signature, or if the {@code N} argument types at position {@code pos}
4930      *          of the target signature
4931      *          (skipping one matching the {@code combiner}'s return type)
4932      *          are not identical with the argument types of {@code combiner}
4933      *
4934      * @see #foldArguments(MethodHandle, MethodHandle)
4935      * @since 9
4936      */
4937     public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4938         MethodType targetType = target.type();
4939         MethodType combinerType = combiner.type();
4940         Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4941         BoundMethodHandle result = target.rebind();
4942         boolean dropResult = rtype == void.class;
4943         LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4944         MethodType newType = targetType;
4945         if (!dropResult) {
4946             newType = newType.dropParameterTypes(pos, pos + 1);
4947         }
4948         result = result.copyWithExtendL(newType, lform, combiner);
4949         return result;
4950     }
4951 






















4952 
4953     private static void checkLoop0(MethodHandle[][] clauses) {
4954         if (clauses == null || clauses.length == 0) {
4955             throw newIllegalArgumentException("null or no clauses passed");
4956         }
4957         if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4958             throw newIllegalArgumentException("null clauses are not allowed");
4959         }
4960         if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4961             throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4962         }
4963     }
4964 
4965     private static void checkLoop1a(int i, MethodHandle in, MethodHandle st) {
4966         if (in.type().returnType() != st.type().returnType()) {
4967             throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4968                     st.type().returnType());
4969         }
4970     }
4971 
4972     private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4973         final List<Class<?>> empty = List.of();
4974         final List<MethodHandle> nonNullInits = init.stream().filter(Objects::nonNull).collect(Collectors.toList());
4975         if (nonNullInits.isEmpty()) {
4976             final List<Class<?>> longest = Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).
4977                     // take only those that can contribute to a common suffix because they are longer than the prefix
4978                     map(MethodHandle::type).filter(t -> t.parameterCount() > cpSize).map(MethodType::parameterList).
4979                     reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4980             return longest.size() == 0 ? empty : longest.subList(cpSize, longest.size());
4981         } else {
4982             return nonNullInits.stream().map(MethodHandle::type).map(MethodType::parameterList).
4983                     reduce((p, q) -> p.size() >= q.size() ? p : q).get();
4984         }
4985     }
4986 
4987     private static void checkLoop1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4988         if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::parameterList).
4989                 anyMatch(pl -> !pl.equals(commonSuffix.subList(0, pl.size())))) {
4990             throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4991                     " (common suffix: " + commonSuffix + ")");
4992         }
4993     }
4994 
4995     private static void checkLoop1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4996         if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4997                 anyMatch(t -> t != loopReturnType)) {
4998             throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4999                     loopReturnType + ")");
5000         }
5001 
5002         if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
5003             throw newIllegalArgumentException("no predicate found", pred);
5004         }
5005         if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
5006                 anyMatch(t -> t != boolean.class)) {
5007             throw newIllegalArgumentException("predicates must have boolean return type", pred);
5008         }
5009     }
5010 
5011     private static void checkLoop2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
5012         final int cpSize = commonParameterSequence.size();
5013         if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
5014                 map(MethodType::parameterList).
5015                 anyMatch(pl -> pl.size() > cpSize || !pl.equals(commonParameterSequence.subList(0, pl.size())))) {
5016             throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
5017                     "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
5018         }
5019     }
5020 
5021     private static void checkIteratedLoop(MethodHandle iterator, MethodHandle body) {
5022         if (null != iterator && !Iterator.class.isAssignableFrom(iterator.type().returnType())) {
5023             throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5024         }
5025         if (null == body) {
5026             throw newIllegalArgumentException("iterated loop body must not be null");
5027         }
5028     }
5029 
5030     private static void checkTryFinally(MethodHandle target, MethodHandle cleanup) {
5031         Class<?> rtype = target.type().returnType();
5032         if (rtype != cleanup.type().returnType()) {
5033             throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5034         }
5035         List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5036         if (!Throwable.class.isAssignableFrom(cleanupParamTypes.get(0))) {
5037             throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5038         }
5039         if (rtype != void.class && cleanupParamTypes.get(1) != rtype) {
5040             throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5041         }
5042         // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5043         // target parameter list.
5044         int cleanupArgIndex = rtype == void.class ? 1 : 2;
5045         List<Class<?>> cleanupArgSuffix = cleanupParamTypes.subList(cleanupArgIndex, cleanupParamTypes.size());
5046         List<Class<?>> targetParamTypes = target.type().parameterList();
5047         if (targetParamTypes.size() < cleanupArgSuffix.size() ||
5048                 !cleanupArgSuffix.equals(targetParamTypes.subList(0, cleanupParamTypes.size() - cleanupArgIndex))) {
5049             throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5050                     cleanup.type(), target.type());
5051         }
5052     }
5053 
5054 }
--- EOF ---