1 /*
   2  * Copyright (c) 2008, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   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
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang.invoke;
  27 
  28 import java.lang.reflect.*;
  29 import java.util.BitSet;
  30 import java.util.List;
  31 import java.util.ArrayList;
  32 import java.util.Arrays;
  33 
  34 import sun.invoke.util.ValueConversions;
  35 import sun.invoke.util.VerifyAccess;
  36 import sun.invoke.util.Wrapper;
  37 import sun.reflect.CallerSensitive;
  38 import sun.reflect.Reflection;
  39 import sun.reflect.misc.ReflectUtil;
  40 import sun.security.util.SecurityConstants;
  41 import java.lang.invoke.LambdaForm.BasicType;
  42 import static java.lang.invoke.LambdaForm.BasicType.*;
  43 import static java.lang.invoke.MethodHandleStatics.*;
  44 import static java.lang.invoke.MethodHandleNatives.Constants.*;
  45 import java.util.concurrent.ConcurrentHashMap;
  46 
  47 /**
  48  * This class consists exclusively of static methods that operate on or return
  49  * method handles. They fall into several categories:
  50  * <ul>
  51  * <li>Lookup methods which help create method handles for methods and fields.
  52  * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
  53  * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
  54  * </ul>
  55  *
  56  * @author John Rose, JSR 292 EG
  57  * @since 1.7
  58  */
  59 public class MethodHandles {
  60 
  61     private MethodHandles() { }  // do not instantiate
  62 
  63     private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
  64     static { MethodHandleImpl.initStatics(); }
  65     // See IMPL_LOOKUP below.
  66 
  67     //// Method handle creation from ordinary methods.
  68 
  69     /**
  70      * Returns a {@link Lookup lookup object} with
  71      * full capabilities to emulate all supported bytecode behaviors of the caller.
  72      * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
  73      * Factory methods on the lookup object can create
  74      * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
  75      * for any member that the caller has access to via bytecodes,
  76      * including protected and private fields and methods.
  77      * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
  78      * Do not store it in place where untrusted code can access it.
  79      * <p>
  80      * This method is caller sensitive, which means that it may return different
  81      * values to different callers.
  82      * <p>
  83      * For any given caller class {@code C}, the lookup object returned by this call
  84      * has equivalent capabilities to any lookup object
  85      * supplied by the JVM to the bootstrap method of an
  86      * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
  87      * executing in the same caller class {@code C}.
  88      * @return a lookup object for the caller of this method, with private access
  89      */
  90     @CallerSensitive
  91     public static Lookup lookup() {
  92         return new Lookup(Reflection.getCallerClass());
  93     }
  94 
  95     /**
  96      * Returns a {@link Lookup lookup object} which is trusted minimally.
  97      * It can only be used to create method handles to
  98      * publicly accessible fields and methods.
  99      * <p>
 100      * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
 101      * of this lookup object will be {@link java.lang.Object}.
 102      *
 103      * <p style="font-size:smaller;">
 104      * <em>Discussion:</em>
 105      * The lookup class can be changed to any other class {@code C} using an expression of the form
 106      * {@link Lookup#in publicLookup().in(C.class)}.
 107      * Since all classes have equal access to public names,
 108      * such a change would confer no new access rights.
 109      * A public lookup object is always subject to
 110      * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
 111      * Also, it cannot access
 112      * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
 113      * @return a lookup object which is trusted minimally
 114      */
 115     public static Lookup publicLookup() {
 116         return Lookup.PUBLIC_LOOKUP;
 117     }
 118 
 119     /**
 120      * Performs an unchecked "crack" of a
 121      * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
 122      * The result is as if the user had obtained a lookup object capable enough
 123      * to crack the target method handle, called
 124      * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
 125      * on the target to obtain its symbolic reference, and then called
 126      * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
 127      * to resolve the symbolic reference to a member.
 128      * <p>
 129      * If there is a security manager, its {@code checkPermission} method
 130      * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
 131      * @param <T> the desired type of the result, either {@link Member} or a subtype
 132      * @param target a direct method handle to crack into symbolic reference components
 133      * @param expected a class object representing the desired result type {@code T}
 134      * @return a reference to the method, constructor, or field object
 135      * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
 136      * @exception NullPointerException if either argument is {@code null}
 137      * @exception IllegalArgumentException if the target is not a direct method handle
 138      * @exception ClassCastException if the member is not of the expected type
 139      * @since 1.8
 140      */
 141     public static <T extends Member> T
 142     reflectAs(Class<T> expected, MethodHandle target) {
 143         SecurityManager smgr = System.getSecurityManager();
 144         if (smgr != null)  smgr.checkPermission(ACCESS_PERMISSION);
 145         Lookup lookup = Lookup.IMPL_LOOKUP;  // use maximally privileged lookup
 146         return lookup.revealDirect(target).reflectAs(expected, lookup);
 147     }
 148     // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
 149     static final private java.security.Permission ACCESS_PERMISSION =
 150         new ReflectPermission("suppressAccessChecks");
 151 
 152     /**
 153      * A <em>lookup object</em> is a factory for creating method handles,
 154      * when the creation requires access checking.
 155      * Method handles do not perform
 156      * access checks when they are called, but rather when they are created.
 157      * Therefore, method handle access
 158      * restrictions must be enforced when a method handle is created.
 159      * The caller class against which those restrictions are enforced
 160      * is known as the {@linkplain #lookupClass lookup class}.
 161      * <p>
 162      * A lookup class which needs to create method handles will call
 163      * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
 164      * When the {@code Lookup} factory object is created, the identity of the lookup class is
 165      * determined, and securely stored in the {@code Lookup} object.
 166      * The lookup class (or its delegates) may then use factory methods
 167      * on the {@code Lookup} object to create method handles for access-checked members.
 168      * This includes all methods, constructors, and fields which are allowed to the lookup class,
 169      * even private ones.
 170      *
 171      * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
 172      * The factory methods on a {@code Lookup} object correspond to all major
 173      * use cases for methods, constructors, and fields.
 174      * Each method handle created by a factory method is the functional
 175      * equivalent of a particular <em>bytecode behavior</em>.
 176      * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
 177      * Here is a summary of the correspondence between these factory methods and
 178      * the behavior the resulting method handles:
 179      * <table border=1 cellpadding=5 summary="lookup method behaviors">
 180      * <tr>
 181      *     <th><a name="equiv"></a>lookup expression</th>
 182      *     <th>member</th>
 183      *     <th>bytecode behavior</th>
 184      * </tr>
 185      * <tr>
 186      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
 187      *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
 188      * </tr>
 189      * <tr>
 190      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
 191      *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
 192      * </tr>
 193      * <tr>
 194      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
 195      *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
 196      * </tr>
 197      * <tr>
 198      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
 199      *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
 200      * </tr>
 201      * <tr>
 202      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
 203      *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
 204      * </tr>
 205      * <tr>
 206      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
 207      *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
 208      * </tr>
 209      * <tr>
 210      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
 211      *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
 212      * </tr>
 213      * <tr>
 214      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
 215      *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
 216      * </tr>
 217      * <tr>
 218      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
 219      *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
 220      * </tr>
 221      * <tr>
 222      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
 223      *     <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
 224      * </tr>
 225      * <tr>
 226      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
 227      *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
 228      * </tr>
 229      * <tr>
 230      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
 231      *     <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
 232      * </tr>
 233      * <tr>
 234      *     <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
 235      *     <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
 236      * </tr>
 237      * </table>
 238      *
 239      * Here, the type {@code C} is the class or interface being searched for a member,
 240      * documented as a parameter named {@code refc} in the lookup methods.
 241      * The method type {@code MT} is composed from the return type {@code T}
 242      * and the sequence of argument types {@code A*}.
 243      * The constructor also has a sequence of argument types {@code A*} and
 244      * is deemed to return the newly-created object of type {@code C}.
 245      * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
 246      * The formal parameter {@code this} stands for the self-reference of type {@code C};
 247      * if it is present, it is always the leading argument to the method handle invocation.
 248      * (In the case of some {@code protected} members, {@code this} may be
 249      * restricted in type to the lookup class; see below.)
 250      * The name {@code arg} stands for all the other method handle arguments.
 251      * In the code examples for the Core Reflection API, the name {@code thisOrNull}
 252      * stands for a null reference if the accessed method or field is static,
 253      * and {@code this} otherwise.
 254      * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
 255      * for reflective objects corresponding to the given members.
 256      * <p>
 257      * In cases where the given member is of variable arity (i.e., a method or constructor)
 258      * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
 259      * In all other cases, the returned method handle will be of fixed arity.
 260      * <p style="font-size:smaller;">
 261      * <em>Discussion:</em>
 262      * The equivalence between looked-up method handles and underlying
 263      * class members and bytecode behaviors
 264      * can break down in a few ways:
 265      * <ul style="font-size:smaller;">
 266      * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
 267      * the lookup can still succeed, even when there is no equivalent
 268      * Java expression or bytecoded constant.
 269      * <li>Likewise, if {@code T} or {@code MT}
 270      * is not symbolically accessible from the lookup class's loader,
 271      * the lookup can still succeed.
 272      * For example, lookups for {@code MethodHandle.invokeExact} and
 273      * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
 274      * <li>If there is a security manager installed, it can forbid the lookup
 275      * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
 276      * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
 277      * constant is not subject to security manager checks.
 278      * <li>If the looked-up method has a
 279      * <a href="MethodHandle.html#maxarity">very large arity</a>,
 280      * the method handle creation may fail, due to the method handle
 281      * type having too many parameters.
 282      * </ul>
 283      *
 284      * <h1><a name="access"></a>Access checking</h1>
 285      * Access checks are applied in the factory methods of {@code Lookup},
 286      * when a method handle is created.
 287      * This is a key difference from the Core Reflection API, since
 288      * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
 289      * performs access checking against every caller, on every call.
 290      * <p>
 291      * All access checks start from a {@code Lookup} object, which
 292      * compares its recorded lookup class against all requests to
 293      * create method handles.
 294      * A single {@code Lookup} object can be used to create any number
 295      * of access-checked method handles, all checked against a single
 296      * lookup class.
 297      * <p>
 298      * A {@code Lookup} object can be shared with other trusted code,
 299      * such as a metaobject protocol.
 300      * A shared {@code Lookup} object delegates the capability
 301      * to create method handles on private members of the lookup class.
 302      * Even if privileged code uses the {@code Lookup} object,
 303      * the access checking is confined to the privileges of the
 304      * original lookup class.
 305      * <p>
 306      * A lookup can fail, because
 307      * the containing class is not accessible to the lookup class, or
 308      * because the desired class member is missing, or because the
 309      * desired class member is not accessible to the lookup class, or
 310      * because the lookup object is not trusted enough to access the member.
 311      * In any of these cases, a {@code ReflectiveOperationException} will be
 312      * thrown from the attempted lookup.  The exact class will be one of
 313      * the following:
 314      * <ul>
 315      * <li>NoSuchMethodException &mdash; if a method is requested but does not exist
 316      * <li>NoSuchFieldException &mdash; if a field is requested but does not exist
 317      * <li>IllegalAccessException &mdash; if the member exists but an access check fails
 318      * </ul>
 319      * <p>
 320      * In general, the conditions under which a method handle may be
 321      * looked up for a method {@code M} are no more restrictive than the conditions
 322      * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
 323      * Where the JVM would raise exceptions like {@code NoSuchMethodError},
 324      * a method handle lookup will generally raise a corresponding
 325      * checked exception, such as {@code NoSuchMethodException}.
 326      * And the effect of invoking the method handle resulting from the lookup
 327      * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
 328      * to executing the compiled, verified, and resolved call to {@code M}.
 329      * The same point is true of fields and constructors.
 330      * <p style="font-size:smaller;">
 331      * <em>Discussion:</em>
 332      * Access checks only apply to named and reflected methods,
 333      * constructors, and fields.
 334      * Other method handle creation methods, such as
 335      * {@link MethodHandle#asType MethodHandle.asType},
 336      * do not require any access checks, and are used
 337      * independently of any {@code Lookup} object.
 338      * <p>
 339      * If the desired member is {@code protected}, the usual JVM rules apply,
 340      * including the requirement that the lookup class must be either be in the
 341      * same package as the desired member, or must inherit that member.
 342      * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
 343      * In addition, if the desired member is a non-static field or method
 344      * in a different package, the resulting method handle may only be applied
 345      * to objects of the lookup class or one of its subclasses.
 346      * This requirement is enforced by narrowing the type of the leading
 347      * {@code this} parameter from {@code C}
 348      * (which will necessarily be a superclass of the lookup class)
 349      * to the lookup class itself.
 350      * <p>
 351      * The JVM imposes a similar requirement on {@code invokespecial} instruction,
 352      * that the receiver argument must match both the resolved method <em>and</em>
 353      * the current class.  Again, this requirement is enforced by narrowing the
 354      * type of the leading parameter to the resulting method handle.
 355      * (See the Java Virtual Machine Specification, section 4.10.1.9.)
 356      * <p>
 357      * The JVM represents constructors and static initializer blocks as internal methods
 358      * with special names ({@code "<init>"} and {@code "<clinit>"}).
 359      * The internal syntax of invocation instructions allows them to refer to such internal
 360      * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
 361      * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
 362      * <p>
 363      * In some cases, access between nested classes is obtained by the Java compiler by creating
 364      * an wrapper method to access a private method of another class
 365      * in the same top-level declaration.
 366      * For example, a nested class {@code C.D}
 367      * can access private members within other related classes such as
 368      * {@code C}, {@code C.D.E}, or {@code C.B},
 369      * but the Java compiler may need to generate wrapper methods in
 370      * those related classes.  In such cases, a {@code Lookup} object on
 371      * {@code C.E} would be unable to those private members.
 372      * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
 373      * which can transform a lookup on {@code C.E} into one on any of those other
 374      * classes, without special elevation of privilege.
 375      * <p>
 376      * The accesses permitted to a given lookup object may be limited,
 377      * according to its set of {@link #lookupModes lookupModes},
 378      * to a subset of members normally accessible to the lookup class.
 379      * For example, the {@link MethodHandles#publicLookup publicLookup}
 380      * method produces a lookup object which is only allowed to access
 381      * public members in public classes.
 382      * The caller sensitive method {@link MethodHandles#lookup lookup}
 383      * produces a lookup object with full capabilities relative to
 384      * its caller class, to emulate all supported bytecode behaviors.
 385      * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
 386      * with fewer access modes than the original lookup object.
 387      *
 388      * <p style="font-size:smaller;">
 389      * <a name="privacc"></a>
 390      * <em>Discussion of private access:</em>
 391      * We say that a lookup has <em>private access</em>
 392      * if its {@linkplain #lookupModes lookup modes}
 393      * include the possibility of accessing {@code private} members.
 394      * As documented in the relevant methods elsewhere,
 395      * only lookups with private access possess the following capabilities:
 396      * <ul style="font-size:smaller;">
 397      * <li>access private fields, methods, and constructors of the lookup class
 398      * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
 399      *     such as {@code Class.forName}
 400      * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
 401      * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
 402      *     for classes accessible to the lookup class
 403      * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
 404      *     within the same package member
 405      * </ul>
 406      * <p style="font-size:smaller;">
 407      * Each of these permissions is a consequence of the fact that a lookup object
 408      * with private access can be securely traced back to an originating class,
 409      * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
 410      * can be reliably determined and emulated by method handles.
 411      *
 412      * <h1><a name="secmgr"></a>Security manager interactions</h1>
 413      * Although bytecode instructions can only refer to classes in
 414      * a related class loader, this API can search for methods in any
 415      * class, as long as a reference to its {@code Class} object is
 416      * available.  Such cross-loader references are also possible with the
 417      * Core Reflection API, and are impossible to bytecode instructions
 418      * such as {@code invokestatic} or {@code getfield}.
 419      * There is a {@linkplain java.lang.SecurityManager security manager API}
 420      * to allow applications to check such cross-loader references.
 421      * These checks apply to both the {@code MethodHandles.Lookup} API
 422      * and the Core Reflection API
 423      * (as found on {@link java.lang.Class Class}).
 424      * <p>
 425      * If a security manager is present, member lookups are subject to
 426      * additional checks.
 427      * From one to three calls are made to the security manager.
 428      * Any of these calls can refuse access by throwing a
 429      * {@link java.lang.SecurityException SecurityException}.
 430      * Define {@code smgr} as the security manager,
 431      * {@code lookc} as the lookup class of the current lookup object,
 432      * {@code refc} as the containing class in which the member
 433      * is being sought, and {@code defc} as the class in which the
 434      * member is actually defined.
 435      * The value {@code lookc} is defined as <em>not present</em>
 436      * if the current lookup object does not have
 437      * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
 438      * The calls are made according to the following rules:
 439      * <ul>
 440      * <li><b>Step 1:</b>
 441      *     If {@code lookc} is not present, or if its class loader is not
 442      *     the same as or an ancestor of the class loader of {@code refc},
 443      *     then {@link SecurityManager#checkPackageAccess
 444      *     smgr.checkPackageAccess(refcPkg)} is called,
 445      *     where {@code refcPkg} is the package of {@code refc}.
 446      * <li><b>Step 2:</b>
 447      *     If the retrieved member is not public and
 448      *     {@code lookc} is not present, then
 449      *     {@link SecurityManager#checkPermission smgr.checkPermission}
 450      *     with {@code RuntimePermission("accessDeclaredMembers")} is called.
 451      * <li><b>Step 3:</b>
 452      *     If the retrieved member is not public,
 453      *     and if {@code lookc} is not present,
 454      *     and if {@code defc} and {@code refc} are different,
 455      *     then {@link SecurityManager#checkPackageAccess
 456      *     smgr.checkPackageAccess(defcPkg)} is called,
 457      *     where {@code defcPkg} is the package of {@code defc}.
 458      * </ul>
 459      * Security checks are performed after other access checks have passed.
 460      * Therefore, the above rules presuppose a member that is public,
 461      * or else that is being accessed from a lookup class that has
 462      * rights to access the member.
 463      *
 464      * <h1><a name="callsens"></a>Caller sensitive methods</h1>
 465      * A small number of Java methods have a special property called caller sensitivity.
 466      * A <em>caller-sensitive</em> method can behave differently depending on the
 467      * identity of its immediate caller.
 468      * <p>
 469      * If a method handle for a caller-sensitive method is requested,
 470      * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
 471      * but they take account of the lookup class in a special way.
 472      * The resulting method handle behaves as if it were called
 473      * from an instruction contained in the lookup class,
 474      * so that the caller-sensitive method detects the lookup class.
 475      * (By contrast, the invoker of the method handle is disregarded.)
 476      * Thus, in the case of caller-sensitive methods,
 477      * different lookup classes may give rise to
 478      * differently behaving method handles.
 479      * <p>
 480      * In cases where the lookup object is
 481      * {@link MethodHandles#publicLookup() publicLookup()},
 482      * or some other lookup object without
 483      * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
 484      * the lookup class is disregarded.
 485      * In such cases, no caller-sensitive method handle can be created,
 486      * access is forbidden, and the lookup fails with an
 487      * {@code IllegalAccessException}.
 488      * <p style="font-size:smaller;">
 489      * <em>Discussion:</em>
 490      * For example, the caller-sensitive method
 491      * {@link java.lang.Class#forName(String) Class.forName(x)}
 492      * can return varying classes or throw varying exceptions,
 493      * depending on the class loader of the class that calls it.
 494      * A public lookup of {@code Class.forName} will fail, because
 495      * there is no reasonable way to determine its bytecode behavior.
 496      * <p style="font-size:smaller;">
 497      * If an application caches method handles for broad sharing,
 498      * it should use {@code publicLookup()} to create them.
 499      * If there is a lookup of {@code Class.forName}, it will fail,
 500      * and the application must take appropriate action in that case.
 501      * It may be that a later lookup, perhaps during the invocation of a
 502      * bootstrap method, can incorporate the specific identity
 503      * of the caller, making the method accessible.
 504      * <p style="font-size:smaller;">
 505      * The function {@code MethodHandles.lookup} is caller sensitive
 506      * so that there can be a secure foundation for lookups.
 507      * Nearly all other methods in the JSR 292 API rely on lookup
 508      * objects to check access requests.
 509      */
 510     public static final
 511     class Lookup {
 512         /** The class on behalf of whom the lookup is being performed. */
 513         private final Class<?> lookupClass;
 514 
 515         /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
 516         private final int allowedModes;
 517 
 518         /** A single-bit mask representing {@code public} access,
 519          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 520          *  The value, {@code 0x01}, happens to be the same as the value of the
 521          *  {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
 522          */
 523         public static final int PUBLIC = Modifier.PUBLIC;
 524 
 525         /** A single-bit mask representing {@code private} access,
 526          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 527          *  The value, {@code 0x02}, happens to be the same as the value of the
 528          *  {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
 529          */
 530         public static final int PRIVATE = Modifier.PRIVATE;
 531 
 532         /** A single-bit mask representing {@code protected} access,
 533          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 534          *  The value, {@code 0x04}, happens to be the same as the value of the
 535          *  {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
 536          */
 537         public static final int PROTECTED = Modifier.PROTECTED;
 538 
 539         /** A single-bit mask representing {@code package} access (default access),
 540          *  which may contribute to the result of {@link #lookupModes lookupModes}.
 541          *  The value is {@code 0x08}, which does not correspond meaningfully to
 542          *  any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
 543          */
 544         public static final int PACKAGE = Modifier.STATIC;
 545 
 546         private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
 547         private static final int TRUSTED   = -1;
 548 
 549         private static int fixmods(int mods) {
 550             mods &= (ALL_MODES - PACKAGE);
 551             return (mods != 0) ? mods : PACKAGE;
 552         }
 553 
 554         /** Tells which class is performing the lookup.  It is this class against
 555          *  which checks are performed for visibility and access permissions.
 556          *  <p>
 557          *  The class implies a maximum level of access permission,
 558          *  but the permissions may be additionally limited by the bitmask
 559          *  {@link #lookupModes lookupModes}, which controls whether non-public members
 560          *  can be accessed.
 561          *  @return the lookup class, on behalf of which this lookup object finds members
 562          */
 563         public Class<?> lookupClass() {
 564             return lookupClass;
 565         }
 566 
 567         // This is just for calling out to MethodHandleImpl.
 568         private Class<?> lookupClassOrNull() {
 569             return (allowedModes == TRUSTED) ? null : lookupClass;
 570         }
 571 
 572         /** Tells which access-protection classes of members this lookup object can produce.
 573          *  The result is a bit-mask of the bits
 574          *  {@linkplain #PUBLIC PUBLIC (0x01)},
 575          *  {@linkplain #PRIVATE PRIVATE (0x02)},
 576          *  {@linkplain #PROTECTED PROTECTED (0x04)},
 577          *  and {@linkplain #PACKAGE PACKAGE (0x08)}.
 578          *  <p>
 579          *  A freshly-created lookup object
 580          *  on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
 581          *  has all possible bits set, since the caller class can access all its own members.
 582          *  A lookup object on a new lookup class
 583          *  {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
 584          *  may have some mode bits set to zero.
 585          *  The purpose of this is to restrict access via the new lookup object,
 586          *  so that it can access only names which can be reached by the original
 587          *  lookup object, and also by the new lookup class.
 588          *  @return the lookup modes, which limit the kinds of access performed by this lookup object
 589          */
 590         public int lookupModes() {
 591             return allowedModes & ALL_MODES;
 592         }
 593 
 594         /** Embody the current class (the lookupClass) as a lookup class
 595          * for method handle creation.
 596          * Must be called by from a method in this package,
 597          * which in turn is called by a method not in this package.
 598          */
 599         Lookup(Class<?> lookupClass) {
 600             this(lookupClass, ALL_MODES);
 601             // make sure we haven't accidentally picked up a privileged class:
 602             checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
 603         }
 604 
 605         private Lookup(Class<?> lookupClass, int allowedModes) {
 606             this.lookupClass = lookupClass;
 607             this.allowedModes = allowedModes;
 608         }
 609 
 610         /**
 611          * Creates a lookup on the specified new lookup class.
 612          * The resulting object will report the specified
 613          * class as its own {@link #lookupClass lookupClass}.
 614          * <p>
 615          * However, the resulting {@code Lookup} object is guaranteed
 616          * to have no more access capabilities than the original.
 617          * In particular, access capabilities can be lost as follows:<ul>
 618          * <li>If the new lookup class differs from the old one,
 619          * protected members will not be accessible by virtue of inheritance.
 620          * (Protected members may continue to be accessible because of package sharing.)
 621          * <li>If the new lookup class is in a different package
 622          * than the old one, protected and default (package) members will not be accessible.
 623          * <li>If the new lookup class is not within the same package member
 624          * as the old one, private members will not be accessible.
 625          * <li>If the new lookup class is not accessible to the old lookup class,
 626          * then no members, not even public members, will be accessible.
 627          * (In all other cases, public members will continue to be accessible.)
 628          * </ul>
 629          *
 630          * @param requestedLookupClass the desired lookup class for the new lookup object
 631          * @return a lookup object which reports the desired lookup class
 632          * @throws NullPointerException if the argument is null
 633          */
 634         public Lookup in(Class<?> requestedLookupClass) {
 635             requestedLookupClass.getClass();  // null check
 636             if (allowedModes == TRUSTED)  // IMPL_LOOKUP can make any lookup at all
 637                 return new Lookup(requestedLookupClass, ALL_MODES);
 638             if (requestedLookupClass == this.lookupClass)
 639                 return this;  // keep same capabilities
 640             int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
 641             if ((newModes & PACKAGE) != 0
 642                 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
 643                 newModes &= ~(PACKAGE|PRIVATE);
 644             }
 645             // Allow nestmate lookups to be created without special privilege:
 646             if ((newModes & PRIVATE) != 0
 647                 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
 648                 newModes &= ~PRIVATE;
 649             }
 650             if ((newModes & PUBLIC) != 0
 651                 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
 652                 // The requested class it not accessible from the lookup class.
 653                 // No permissions.
 654                 newModes = 0;
 655             }
 656             checkUnprivilegedlookupClass(requestedLookupClass, newModes);
 657             return new Lookup(requestedLookupClass, newModes);
 658         }
 659 
 660         // Make sure outer class is initialized first.
 661         static { IMPL_NAMES.getClass(); }
 662 
 663         /** Version of lookup which is trusted minimally.
 664          *  It can only be used to create method handles to
 665          *  publicly accessible members.
 666          */
 667         static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
 668 
 669         /** Package-private version of lookup which is trusted. */
 670         static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
 671 
 672         private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
 673             String name = lookupClass.getName();
 674             if (name.startsWith("java.lang.invoke."))
 675                 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
 676 
 677             // For caller-sensitive MethodHandles.lookup()
 678             // disallow lookup more restricted packages
 679             if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
 680                 if (name.startsWith("java.") ||
 681                         (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
 682                     throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
 683                 }
 684             }
 685         }
 686 
 687         /**
 688          * Displays the name of the class from which lookups are to be made.
 689          * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
 690          * If there are restrictions on the access permitted to this lookup,
 691          * this is indicated by adding a suffix to the class name, consisting
 692          * of a slash and a keyword.  The keyword represents the strongest
 693          * allowed access, and is chosen as follows:
 694          * <ul>
 695          * <li>If no access is allowed, the suffix is "/noaccess".
 696          * <li>If only public access is allowed, the suffix is "/public".
 697          * <li>If only public and package access are allowed, the suffix is "/package".
 698          * <li>If only public, package, and private access are allowed, the suffix is "/private".
 699          * </ul>
 700          * If none of the above cases apply, it is the case that full
 701          * access (public, package, private, and protected) is allowed.
 702          * In this case, no suffix is added.
 703          * This is true only of an object obtained originally from
 704          * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
 705          * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
 706          * always have restricted access, and will display a suffix.
 707          * <p>
 708          * (It may seem strange that protected access should be
 709          * stronger than private access.  Viewed independently from
 710          * package access, protected access is the first to be lost,
 711          * because it requires a direct subclass relationship between
 712          * caller and callee.)
 713          * @see #in
 714          */
 715         @Override
 716         public String toString() {
 717             String cname = lookupClass.getName();
 718             switch (allowedModes) {
 719             case 0:  // no privileges
 720                 return cname + "/noaccess";
 721             case PUBLIC:
 722                 return cname + "/public";
 723             case PUBLIC|PACKAGE:
 724                 return cname + "/package";
 725             case ALL_MODES & ~PROTECTED:
 726                 return cname + "/private";
 727             case ALL_MODES:
 728                 return cname;
 729             case TRUSTED:
 730                 return "/trusted";  // internal only; not exported
 731             default:  // Should not happen, but it's a bitfield...
 732                 cname = cname + "/" + Integer.toHexString(allowedModes);
 733                 assert(false) : cname;
 734                 return cname;
 735             }
 736         }
 737 
 738         /**
 739          * Produces a method handle for a static method.
 740          * The type of the method handle will be that of the method.
 741          * (Since static methods do not take receivers, there is no
 742          * additional receiver argument inserted into the method handle type,
 743          * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
 744          * The method and all its argument types must be accessible to the lookup object.
 745          * <p>
 746          * The returned method handle will have
 747          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 748          * the method's variable arity modifier bit ({@code 0x0080}) is set.
 749          * <p>
 750          * If the returned method handle is invoked, the method's class will
 751          * be initialized, if it has not already been initialized.
 752          * <p><b>Example:</b>
 753          * <blockquote><pre>{@code
 754 import static java.lang.invoke.MethodHandles.*;
 755 import static java.lang.invoke.MethodType.*;
 756 ...
 757 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
 758   "asList", methodType(List.class, Object[].class));
 759 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
 760          * }</pre></blockquote>
 761          * @param refc the class from which the method is accessed
 762          * @param name the name of the method
 763          * @param type the type of the method
 764          * @return the desired method handle
 765          * @throws NoSuchMethodException if the method does not exist
 766          * @throws IllegalAccessException if access checking fails,
 767          *                                or if the method is not {@code static},
 768          *                                or if the method's variable arity modifier bit
 769          *                                is set and {@code asVarargsCollector} fails
 770          * @exception SecurityException if a security manager is present and it
 771          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
 772          * @throws NullPointerException if any argument is null
 773          */
 774         public
 775         MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
 776             MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
 777             return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
 778         }
 779 
 780         /**
 781          * Produces a method handle for a virtual method.
 782          * The type of the method handle will be that of the method,
 783          * with the receiver type (usually {@code refc}) prepended.
 784          * The method and all its argument types must be accessible to the lookup object.
 785          * <p>
 786          * When called, the handle will treat the first argument as a receiver
 787          * and dispatch on the receiver's type to determine which method
 788          * implementation to enter.
 789          * (The dispatching action is identical with that performed by an
 790          * {@code invokevirtual} or {@code invokeinterface} instruction.)
 791          * <p>
 792          * The first argument will be of type {@code refc} if the lookup
 793          * class has full privileges to access the member.  Otherwise
 794          * the member must be {@code protected} and the first argument
 795          * will be restricted in type to the lookup class.
 796          * <p>
 797          * The returned method handle will have
 798          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 799          * the method's variable arity modifier bit ({@code 0x0080}) is set.
 800          * <p>
 801          * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
 802          * instructions and method handles produced by {@code findVirtual},
 803          * if the class is {@code MethodHandle} and the name string is
 804          * {@code invokeExact} or {@code invoke}, the resulting
 805          * method handle is equivalent to one produced by
 806          * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
 807          * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
 808          * with the same {@code type} argument.
 809          *
 810          * <b>Example:</b>
 811          * <blockquote><pre>{@code
 812 import static java.lang.invoke.MethodHandles.*;
 813 import static java.lang.invoke.MethodType.*;
 814 ...
 815 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
 816   "concat", methodType(String.class, String.class));
 817 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
 818   "hashCode", methodType(int.class));
 819 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
 820   "hashCode", methodType(int.class));
 821 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
 822 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
 823 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
 824 // interface method:
 825 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
 826   "subSequence", methodType(CharSequence.class, int.class, int.class));
 827 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
 828 // constructor "internal method" must be accessed differently:
 829 MethodType MT_newString = methodType(void.class); //()V for new String()
 830 try { assertEquals("impossible", lookup()
 831         .findVirtual(String.class, "<init>", MT_newString));
 832  } catch (NoSuchMethodException ex) { } // OK
 833 MethodHandle MH_newString = publicLookup()
 834   .findConstructor(String.class, MT_newString);
 835 assertEquals("", (String) MH_newString.invokeExact());
 836          * }</pre></blockquote>
 837          *
 838          * @param refc the class or interface from which the method is accessed
 839          * @param name the name of the method
 840          * @param type the type of the method, with the receiver argument omitted
 841          * @return the desired method handle
 842          * @throws NoSuchMethodException if the method does not exist
 843          * @throws IllegalAccessException if access checking fails,
 844          *                                or if the method is {@code static}
 845          *                                or if the method's variable arity modifier bit
 846          *                                is set and {@code asVarargsCollector} fails
 847          * @exception SecurityException if a security manager is present and it
 848          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
 849          * @throws NullPointerException if any argument is null
 850          */
 851         public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
 852             if (refc == MethodHandle.class) {
 853                 MethodHandle mh = findVirtualForMH(name, type);
 854                 if (mh != null)  return mh;
 855             }
 856             byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
 857             MemberName method = resolveOrFail(refKind, refc, name, type);
 858             return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
 859         }
 860         private MethodHandle findVirtualForMH(String name, MethodType type) {
 861             // these names require special lookups because of the implicit MethodType argument
 862             if ("invoke".equals(name))
 863                 return invoker(type);
 864             if ("invokeExact".equals(name))
 865                 return exactInvoker(type);
 866             if ("invokeBasic".equals(name))
 867                 return basicInvoker(type);
 868             assert(!MemberName.isMethodHandleInvokeName(name));
 869             return null;
 870         }
 871 
 872         /**
 873          * Produces a method handle which creates an object and initializes it, using
 874          * the constructor of the specified type.
 875          * The parameter types of the method handle will be those of the constructor,
 876          * while the return type will be a reference to the constructor's class.
 877          * The constructor and all its argument types must be accessible to the lookup object.
 878          * <p>
 879          * The requested type must have a return type of {@code void}.
 880          * (This is consistent with the JVM's treatment of constructor type descriptors.)
 881          * <p>
 882          * The returned method handle will have
 883          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 884          * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
 885          * <p>
 886          * If the returned method handle is invoked, the constructor's class will
 887          * be initialized, if it has not already been initialized.
 888          * <p><b>Example:</b>
 889          * <blockquote><pre>{@code
 890 import static java.lang.invoke.MethodHandles.*;
 891 import static java.lang.invoke.MethodType.*;
 892 ...
 893 MethodHandle MH_newArrayList = publicLookup().findConstructor(
 894   ArrayList.class, methodType(void.class, Collection.class));
 895 Collection orig = Arrays.asList("x", "y");
 896 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
 897 assert(orig != copy);
 898 assertEquals(orig, copy);
 899 // a variable-arity constructor:
 900 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
 901   ProcessBuilder.class, methodType(void.class, String[].class));
 902 ProcessBuilder pb = (ProcessBuilder)
 903   MH_newProcessBuilder.invoke("x", "y", "z");
 904 assertEquals("[x, y, z]", pb.command().toString());
 905          * }</pre></blockquote>
 906          * @param refc the class or interface from which the method is accessed
 907          * @param type the type of the method, with the receiver argument omitted, and a void return type
 908          * @return the desired method handle
 909          * @throws NoSuchMethodException if the constructor does not exist
 910          * @throws IllegalAccessException if access checking fails
 911          *                                or if the method's variable arity modifier bit
 912          *                                is set and {@code asVarargsCollector} fails
 913          * @exception SecurityException if a security manager is present and it
 914          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
 915          * @throws NullPointerException if any argument is null
 916          */
 917         public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
 918             String name = "<init>";
 919             MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
 920             return getDirectConstructor(refc, ctor);
 921         }
 922 
 923         /**
 924          * Produces an early-bound method handle for a virtual method.
 925          * It will bypass checks for overriding methods on the receiver,
 926          * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
 927          * instruction from within the explicitly specified {@code specialCaller}.
 928          * The type of the method handle will be that of the method,
 929          * with a suitably restricted receiver type prepended.
 930          * (The receiver type will be {@code specialCaller} or a subtype.)
 931          * The method and all its argument types must be accessible
 932          * to the lookup object.
 933          * <p>
 934          * Before method resolution,
 935          * if the explicitly specified caller class is not identical with the
 936          * lookup class, or if this lookup object does not have
 937          * <a href="MethodHandles.Lookup.html#privacc">private access</a>
 938          * privileges, the access fails.
 939          * <p>
 940          * The returned method handle will have
 941          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
 942          * the method's variable arity modifier bit ({@code 0x0080}) is set.
 943          * <p style="font-size:smaller;">
 944          * <em>(Note:  JVM internal methods named {@code "<init>"} are not visible to this API,
 945          * even though the {@code invokespecial} instruction can refer to them
 946          * in special circumstances.  Use {@link #findConstructor findConstructor}
 947          * to access instance initialization methods in a safe manner.)</em>
 948          * <p><b>Example:</b>
 949          * <blockquote><pre>{@code
 950 import static java.lang.invoke.MethodHandles.*;
 951 import static java.lang.invoke.MethodType.*;
 952 ...
 953 static class Listie extends ArrayList {
 954   public String toString() { return "[wee Listie]"; }
 955   static Lookup lookup() { return MethodHandles.lookup(); }
 956 }
 957 ...
 958 // no access to constructor via invokeSpecial:
 959 MethodHandle MH_newListie = Listie.lookup()
 960   .findConstructor(Listie.class, methodType(void.class));
 961 Listie l = (Listie) MH_newListie.invokeExact();
 962 try { assertEquals("impossible", Listie.lookup().findSpecial(
 963         Listie.class, "<init>", methodType(void.class), Listie.class));
 964  } catch (NoSuchMethodException ex) { } // OK
 965 // access to super and self methods via invokeSpecial:
 966 MethodHandle MH_super = Listie.lookup().findSpecial(
 967   ArrayList.class, "toString" , methodType(String.class), Listie.class);
 968 MethodHandle MH_this = Listie.lookup().findSpecial(
 969   Listie.class, "toString" , methodType(String.class), Listie.class);
 970 MethodHandle MH_duper = Listie.lookup().findSpecial(
 971   Object.class, "toString" , methodType(String.class), Listie.class);
 972 assertEquals("[]", (String) MH_super.invokeExact(l));
 973 assertEquals(""+l, (String) MH_this.invokeExact(l));
 974 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
 975 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
 976         String.class, "toString", methodType(String.class), Listie.class));
 977  } catch (IllegalAccessException ex) { } // OK
 978 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
 979 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
 980          * }</pre></blockquote>
 981          *
 982          * @param refc the class or interface from which the method is accessed
 983          * @param name the name of the method (which must not be "&lt;init&gt;")
 984          * @param type the type of the method, with the receiver argument omitted
 985          * @param specialCaller the proposed calling class to perform the {@code invokespecial}
 986          * @return the desired method handle
 987          * @throws NoSuchMethodException if the method does not exist
 988          * @throws IllegalAccessException if access checking fails
 989          *                                or if the method's variable arity modifier bit
 990          *                                is set and {@code asVarargsCollector} fails
 991          * @exception SecurityException if a security manager is present and it
 992          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
 993          * @throws NullPointerException if any argument is null
 994          */
 995         public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
 996                                         Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
 997             checkSpecialCaller(specialCaller);
 998             Lookup specialLookup = this.in(specialCaller);
 999             MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1000             return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1001         }
1002 
1003         /**
1004          * Produces a method handle giving read access to a non-static field.
1005          * The type of the method handle will have a return type of the field's
1006          * value type.
1007          * The method handle's single argument will be the instance containing
1008          * the field.
1009          * Access checking is performed immediately on behalf of the lookup class.
1010          * @param refc the class or interface from which the method is accessed
1011          * @param name the field's name
1012          * @param type the field's type
1013          * @return a method handle which can load values from the field
1014          * @throws NoSuchFieldException if the field does not exist
1015          * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1016          * @exception SecurityException if a security manager is present and it
1017          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1018          * @throws NullPointerException if any argument is null
1019          */
1020         public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1021             MemberName field = resolveOrFail(REF_getField, refc, name, type);
1022             return getDirectField(REF_getField, refc, field);
1023         }
1024 
1025         /**
1026          * Produces a method handle giving write access to a non-static field.
1027          * The type of the method handle will have a void return type.
1028          * The method handle will take two arguments, the instance containing
1029          * the field, and the value to be stored.
1030          * The second argument will be of the field's value type.
1031          * Access checking is performed immediately on behalf of the lookup class.
1032          * @param refc the class or interface from which the method is accessed
1033          * @param name the field's name
1034          * @param type the field's type
1035          * @return a method handle which can store values into the field
1036          * @throws NoSuchFieldException if the field does not exist
1037          * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1038          * @exception SecurityException if a security manager is present and it
1039          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1040          * @throws NullPointerException if any argument is null
1041          */
1042         public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1043             MemberName field = resolveOrFail(REF_putField, refc, name, type);
1044             return getDirectField(REF_putField, refc, field);
1045         }
1046 
1047         /**
1048          * Produces a method handle giving read access to a static field.
1049          * The type of the method handle will have a return type of the field's
1050          * value type.
1051          * The method handle will take no arguments.
1052          * Access checking is performed immediately on behalf of the lookup class.
1053          * <p>
1054          * If the returned method handle is invoked, the field's class will
1055          * be initialized, if it has not already been initialized.
1056          * @param refc the class or interface from which the method is accessed
1057          * @param name the field's name
1058          * @param type the field's type
1059          * @return a method handle which can load values from the field
1060          * @throws NoSuchFieldException if the field does not exist
1061          * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1062          * @exception SecurityException if a security manager is present and it
1063          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1064          * @throws NullPointerException if any argument is null
1065          */
1066         public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1067             MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1068             return getDirectField(REF_getStatic, refc, field);
1069         }
1070 
1071         /**
1072          * Produces a method handle giving write access to a static field.
1073          * The type of the method handle will have a void return type.
1074          * The method handle will take a single
1075          * argument, of the field's value type, the value to be stored.
1076          * Access checking is performed immediately on behalf of the lookup class.
1077          * <p>
1078          * If the returned method handle is invoked, the field's class will
1079          * be initialized, if it has not already been initialized.
1080          * @param refc the class or interface from which the method is accessed
1081          * @param name the field's name
1082          * @param type the field's type
1083          * @return a method handle which can store values into the field
1084          * @throws NoSuchFieldException if the field does not exist
1085          * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1086          * @exception SecurityException if a security manager is present and it
1087          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1088          * @throws NullPointerException if any argument is null
1089          */
1090         public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1091             MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1092             return getDirectField(REF_putStatic, refc, field);
1093         }
1094 
1095         /**
1096          * Produces an early-bound method handle for a non-static method.
1097          * The receiver must have a supertype {@code defc} in which a method
1098          * of the given name and type is accessible to the lookup class.
1099          * The method and all its argument types must be accessible to the lookup object.
1100          * The type of the method handle will be that of the method,
1101          * without any insertion of an additional receiver parameter.
1102          * The given receiver will be bound into the method handle,
1103          * so that every call to the method handle will invoke the
1104          * requested method on the given receiver.
1105          * <p>
1106          * The returned method handle will have
1107          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1108          * the method's variable arity modifier bit ({@code 0x0080}) is set
1109          * <em>and</em> the trailing array argument is not the only argument.
1110          * (If the trailing array argument is the only argument,
1111          * the given receiver value will be bound to it.)
1112          * <p>
1113          * This is equivalent to the following code:
1114          * <blockquote><pre>{@code
1115 import static java.lang.invoke.MethodHandles.*;
1116 import static java.lang.invoke.MethodType.*;
1117 ...
1118 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1119 MethodHandle mh1 = mh0.bindTo(receiver);
1120 MethodType mt1 = mh1.type();
1121 if (mh0.isVarargsCollector())
1122   mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
1123 return mh1;
1124          * }</pre></blockquote>
1125          * where {@code defc} is either {@code receiver.getClass()} or a super
1126          * type of that class, in which the requested method is accessible
1127          * to the lookup class.
1128          * (Note that {@code bindTo} does not preserve variable arity.)
1129          * @param receiver the object from which the method is accessed
1130          * @param name the name of the method
1131          * @param type the type of the method, with the receiver argument omitted
1132          * @return the desired method handle
1133          * @throws NoSuchMethodException if the method does not exist
1134          * @throws IllegalAccessException if access checking fails
1135          *                                or if the method's variable arity modifier bit
1136          *                                is set and {@code asVarargsCollector} fails
1137          * @exception SecurityException if a security manager is present and it
1138          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1139          * @throws NullPointerException if any argument is null
1140          * @see MethodHandle#bindTo
1141          * @see #findVirtual
1142          */
1143         public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1144             Class<? extends Object> refc = receiver.getClass(); // may get NPE
1145             MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1146             MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1147             return mh.bindArgumentL(0, receiver).setVarargs(method);
1148         }
1149 
1150         /**
1151          * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1152          * to <i>m</i>, if the lookup class has permission.
1153          * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1154          * If <i>m</i> is virtual, overriding is respected on every call.
1155          * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1156          * The type of the method handle will be that of the method,
1157          * with the receiver type prepended (but only if it is non-static).
1158          * If the method's {@code accessible} flag is not set,
1159          * access checking is performed immediately on behalf of the lookup class.
1160          * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1161          * <p>
1162          * The returned method handle will have
1163          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1164          * the method's variable arity modifier bit ({@code 0x0080}) is set.
1165          * <p>
1166          * If <i>m</i> is static, and
1167          * if the returned method handle is invoked, the method's class will
1168          * be initialized, if it has not already been initialized.
1169          * @param m the reflected method
1170          * @return a method handle which can invoke the reflected method
1171          * @throws IllegalAccessException if access checking fails
1172          *                                or if the method's variable arity modifier bit
1173          *                                is set and {@code asVarargsCollector} fails
1174          * @throws NullPointerException if the argument is null
1175          */
1176         public MethodHandle unreflect(Method m) throws IllegalAccessException {
1177             if (m.getDeclaringClass() == MethodHandle.class) {
1178                 MethodHandle mh = unreflectForMH(m);
1179                 if (mh != null)  return mh;
1180             }
1181             MemberName method = new MemberName(m);
1182             byte refKind = method.getReferenceKind();
1183             if (refKind == REF_invokeSpecial)
1184                 refKind = REF_invokeVirtual;
1185             assert(method.isMethod());
1186             Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1187             return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1188         }
1189         private MethodHandle unreflectForMH(Method m) {
1190             // these names require special lookups because they throw UnsupportedOperationException
1191             if (MemberName.isMethodHandleInvokeName(m.getName()))
1192                 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1193             return null;
1194         }
1195 
1196         /**
1197          * Produces a method handle for a reflected method.
1198          * It will bypass checks for overriding methods on the receiver,
1199          * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1200          * instruction from within the explicitly specified {@code specialCaller}.
1201          * The type of the method handle will be that of the method,
1202          * with a suitably restricted receiver type prepended.
1203          * (The receiver type will be {@code specialCaller} or a subtype.)
1204          * If the method's {@code accessible} flag is not set,
1205          * access checking is performed immediately on behalf of the lookup class,
1206          * as if {@code invokespecial} instruction were being linked.
1207          * <p>
1208          * Before method resolution,
1209          * if the explicitly specified caller class is not identical with the
1210          * lookup class, or if this lookup object does not have
1211          * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1212          * privileges, the access fails.
1213          * <p>
1214          * The returned method handle will have
1215          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1216          * the method's variable arity modifier bit ({@code 0x0080}) is set.
1217          * @param m the reflected method
1218          * @param specialCaller the class nominally calling the method
1219          * @return a method handle which can invoke the reflected method
1220          * @throws IllegalAccessException if access checking fails
1221          *                                or if the method's variable arity modifier bit
1222          *                                is set and {@code asVarargsCollector} fails
1223          * @throws NullPointerException if any argument is null
1224          */
1225         public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1226             checkSpecialCaller(specialCaller);
1227             Lookup specialLookup = this.in(specialCaller);
1228             MemberName method = new MemberName(m, true);
1229             assert(method.isMethod());
1230             // ignore m.isAccessible:  this is a new kind of access
1231             return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1232         }
1233 
1234         /**
1235          * Produces a method handle for a reflected constructor.
1236          * The type of the method handle will be that of the constructor,
1237          * with the return type changed to the declaring class.
1238          * The method handle will perform a {@code newInstance} operation,
1239          * creating a new instance of the constructor's class on the
1240          * arguments passed to the method handle.
1241          * <p>
1242          * If the constructor's {@code accessible} flag is not set,
1243          * access checking is performed immediately on behalf of the lookup class.
1244          * <p>
1245          * The returned method handle will have
1246          * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1247          * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1248          * <p>
1249          * If the returned method handle is invoked, the constructor's class will
1250          * be initialized, if it has not already been initialized.
1251          * @param c the reflected constructor
1252          * @return a method handle which can invoke the reflected constructor
1253          * @throws IllegalAccessException if access checking fails
1254          *                                or if the method's variable arity modifier bit
1255          *                                is set and {@code asVarargsCollector} fails
1256          * @throws NullPointerException if the argument is null
1257          */
1258         public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1259             MemberName ctor = new MemberName(c);
1260             assert(ctor.isConstructor());
1261             Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1262             return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1263         }
1264 
1265         /**
1266          * Produces a method handle giving read access to a reflected field.
1267          * The type of the method handle will have a return type of the field's
1268          * value type.
1269          * If the field is static, the method handle will take no arguments.
1270          * Otherwise, its single argument will be the instance containing
1271          * the field.
1272          * If the field's {@code accessible} flag is not set,
1273          * access checking is performed immediately on behalf of the lookup class.
1274          * <p>
1275          * If the field is static, and
1276          * if the returned method handle is invoked, the field's class will
1277          * be initialized, if it has not already been initialized.
1278          * @param f the reflected field
1279          * @return a method handle which can load values from the reflected field
1280          * @throws IllegalAccessException if access checking fails
1281          * @throws NullPointerException if the argument is null
1282          */
1283         public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1284             return unreflectField(f, false);
1285         }
1286         private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1287             MemberName field = new MemberName(f, isSetter);
1288             assert(isSetter
1289                     ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1290                     : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1291             Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1292             return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1293         }
1294 
1295         /**
1296          * Produces a method handle giving write access to a reflected field.
1297          * The type of the method handle will have a void return type.
1298          * If the field is static, the method handle will take a single
1299          * argument, of the field's value type, the value to be stored.
1300          * Otherwise, the two arguments will be the instance containing
1301          * the field, and the value to be stored.
1302          * If the field's {@code accessible} flag is not set,
1303          * access checking is performed immediately on behalf of the lookup class.
1304          * <p>
1305          * If the field is static, and
1306          * if the returned method handle is invoked, the field's class will
1307          * be initialized, if it has not already been initialized.
1308          * @param f the reflected field
1309          * @return a method handle which can store values into the reflected field
1310          * @throws IllegalAccessException if access checking fails
1311          * @throws NullPointerException if the argument is null
1312          */
1313         public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1314             return unreflectField(f, true);
1315         }
1316 
1317         /**
1318          * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1319          * created by this lookup object or a similar one.
1320          * Security and access checks are performed to ensure that this lookup object
1321          * is capable of reproducing the target method handle.
1322          * This means that the cracking may fail if target is a direct method handle
1323          * but was created by an unrelated lookup object.
1324          * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1325          * and was created by a lookup object for a different class.
1326          * @param target a direct method handle to crack into symbolic reference components
1327          * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1328          * @exception SecurityException if a security manager is present and it
1329          *                              <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1330          * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1331          * @exception NullPointerException if the target is {@code null}
1332          * @see MethodHandleInfo
1333          * @since 1.8
1334          */
1335         public MethodHandleInfo revealDirect(MethodHandle target) {
1336             MemberName member = target.internalMemberName();
1337             if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
1338                 throw newIllegalArgumentException("not a direct method handle");
1339             Class<?> defc = member.getDeclaringClass();
1340             byte refKind = member.getReferenceKind();
1341             assert(MethodHandleNatives.refKindIsValid(refKind));
1342             if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1343                 // Devirtualized method invocation is usually formally virtual.
1344                 // To avoid creating extra MemberName objects for this common case,
1345                 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1346                 refKind = REF_invokeVirtual;
1347             if (refKind == REF_invokeVirtual && defc.isInterface())
1348                 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1349                 refKind = REF_invokeInterface;
1350             // Check SM permissions and member access before cracking.
1351             try {
1352                 checkAccess(refKind, defc, member);
1353                 checkSecurityManager(defc, member);
1354             } catch (IllegalAccessException ex) {
1355                 throw new IllegalArgumentException(ex);
1356             }
1357             if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1358                 Class<?> callerClass = target.internalCallerClass();
1359                 if (!hasPrivateAccess() || callerClass != lookupClass())
1360                     throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1361             }
1362             // Produce the handle to the results.
1363             return new InfoFromMemberName(this, member, refKind);
1364         }
1365 
1366         /// Helper methods, all package-private.
1367 
1368         MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1369             checkSymbolicClass(refc);  // do this before attempting to resolve
1370             name.getClass();  // NPE
1371             type.getClass();  // NPE
1372             return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1373                                             NoSuchFieldException.class);
1374         }
1375 
1376         MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1377             checkSymbolicClass(refc);  // do this before attempting to resolve
1378             name.getClass();  // NPE
1379             type.getClass();  // NPE
1380             checkMethodName(refKind, name);  // NPE check on name
1381             return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1382                                             NoSuchMethodException.class);
1383         }
1384 
1385         MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1386             checkSymbolicClass(member.getDeclaringClass());  // do this before attempting to resolve
1387             member.getName().getClass();  // NPE
1388             member.getType().getClass();  // NPE
1389             return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1390                                             ReflectiveOperationException.class);
1391         }
1392 
1393         void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1394             refc.getClass();  // NPE
1395             Class<?> caller = lookupClassOrNull();
1396             if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1397                 throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
1398         }
1399 
1400         /** Check name for an illegal leading "&lt;" character. */
1401         void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1402             if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1403                 throw new NoSuchMethodException("illegal method name: "+name);
1404         }
1405 
1406 
1407         /**
1408          * Find my trustable caller class if m is a caller sensitive method.
1409          * If this lookup object has private access, then the caller class is the lookupClass.
1410          * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1411          */
1412         Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1413             Class<?> callerClass = null;
1414             if (MethodHandleNatives.isCallerSensitive(m)) {
1415                 // Only lookups with private access are allowed to resolve caller-sensitive methods
1416                 if (hasPrivateAccess()) {
1417                     callerClass = lookupClass;
1418                 } else {
1419                     throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1420                 }
1421             }
1422             return callerClass;
1423         }
1424 
1425         private boolean hasPrivateAccess() {
1426             return (allowedModes & PRIVATE) != 0;
1427         }
1428 
1429         /**
1430          * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1431          * Determines a trustable caller class to compare with refc, the symbolic reference class.
1432          * If this lookup object has private access, then the caller class is the lookupClass.
1433          */
1434         void checkSecurityManager(Class<?> refc, MemberName m) {
1435             SecurityManager smgr = System.getSecurityManager();
1436             if (smgr == null)  return;
1437             if (allowedModes == TRUSTED)  return;
1438 
1439             // Step 1:
1440             boolean fullPowerLookup = hasPrivateAccess();
1441             if (!fullPowerLookup ||
1442                 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1443                 ReflectUtil.checkPackageAccess(refc);
1444             }
1445 
1446             // Step 2:
1447             if (m.isPublic()) return;
1448             if (!fullPowerLookup) {
1449                 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1450             }
1451 
1452             // Step 3:
1453             Class<?> defc = m.getDeclaringClass();
1454             if (!fullPowerLookup && defc != refc) {
1455                 ReflectUtil.checkPackageAccess(defc);
1456             }
1457         }
1458 
1459         void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1460             boolean wantStatic = (refKind == REF_invokeStatic);
1461             String message;
1462             if (m.isConstructor())
1463                 message = "expected a method, not a constructor";
1464             else if (!m.isMethod())
1465                 message = "expected a method";
1466             else if (wantStatic != m.isStatic())
1467                 message = wantStatic ? "expected a static method" : "expected a non-static method";
1468             else
1469                 { checkAccess(refKind, refc, m); return; }
1470             throw m.makeAccessException(message, this);
1471         }
1472 
1473         void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1474             boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1475             String message;
1476             if (wantStatic != m.isStatic())
1477                 message = wantStatic ? "expected a static field" : "expected a non-static field";
1478             else
1479                 { checkAccess(refKind, refc, m); return; }
1480             throw m.makeAccessException(message, this);
1481         }
1482 
1483         /** Check public/protected/private bits on the symbolic reference class and its member. */
1484         void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1485             assert(m.referenceKindIsConsistentWith(refKind) &&
1486                    MethodHandleNatives.refKindIsValid(refKind) &&
1487                    (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1488             int allowedModes = this.allowedModes;
1489             if (allowedModes == TRUSTED)  return;
1490             int mods = m.getModifiers();
1491             if (Modifier.isProtected(mods) &&
1492                     refKind == REF_invokeVirtual &&
1493                     m.getDeclaringClass() == Object.class &&
1494                     m.getName().equals("clone") &&
1495                     refc.isArray()) {
1496                 // The JVM does this hack also.
1497                 // (See ClassVerifier::verify_invoke_instructions
1498                 // and LinkResolver::check_method_accessability.)
1499                 // Because the JVM does not allow separate methods on array types,
1500                 // there is no separate method for int[].clone.
1501                 // All arrays simply inherit Object.clone.
1502                 // But for access checking logic, we make Object.clone
1503                 // (normally protected) appear to be public.
1504                 // Later on, when the DirectMethodHandle is created,
1505                 // its leading argument will be restricted to the
1506                 // requested array type.
1507                 // N.B. The return type is not adjusted, because
1508                 // that is *not* the bytecode behavior.
1509                 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1510             }
1511             if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1512                 // cannot "new" a protected ctor in a different package
1513                 mods ^= Modifier.PROTECTED;
1514             }
1515             if (Modifier.isFinal(mods) &&
1516                     MethodHandleNatives.refKindIsSetter(refKind))
1517                 throw m.makeAccessException("unexpected set of a final field", this);
1518             if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
1519                 return;  // common case
1520             int requestedModes = fixmods(mods);  // adjust 0 => PACKAGE
1521             if ((requestedModes & allowedModes) != 0) {
1522                 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1523                                                     mods, lookupClass(), allowedModes))
1524                     return;
1525             } else {
1526                 // Protected members can also be checked as if they were package-private.
1527                 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1528                         && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1529                     return;
1530             }
1531             throw m.makeAccessException(accessFailedMessage(refc, m), this);
1532         }
1533 
1534         String accessFailedMessage(Class<?> refc, MemberName m) {
1535             Class<?> defc = m.getDeclaringClass();
1536             int mods = m.getModifiers();
1537             // check the class first:
1538             boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1539                                (defc == refc ||
1540                                 Modifier.isPublic(refc.getModifiers())));
1541             if (!classOK && (allowedModes & PACKAGE) != 0) {
1542                 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1543                            (defc == refc ||
1544                             VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1545             }
1546             if (!classOK)
1547                 return "class is not public";
1548             if (Modifier.isPublic(mods))
1549                 return "access to public member failed";  // (how?)
1550             if (Modifier.isPrivate(mods))
1551                 return "member is private";
1552             if (Modifier.isProtected(mods))
1553                 return "member is protected";
1554             return "member is private to package";
1555         }
1556 
1557         private static final boolean ALLOW_NESTMATE_ACCESS = false;
1558 
1559         private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
1560             int allowedModes = this.allowedModes;
1561             if (allowedModes == TRUSTED)  return;
1562             if (!hasPrivateAccess()
1563                 || (specialCaller != lookupClass()
1564                     && !(ALLOW_NESTMATE_ACCESS &&
1565                          VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1566                 throw new MemberName(specialCaller).
1567                     makeAccessException("no private access for invokespecial", this);
1568         }
1569 
1570         private boolean restrictProtectedReceiver(MemberName method) {
1571             // The accessing class only has the right to use a protected member
1572             // on itself or a subclass.  Enforce that restriction, from JVMS 5.4.4, etc.
1573             if (!method.isProtected() || method.isStatic()
1574                 || allowedModes == TRUSTED
1575                 || method.getDeclaringClass() == lookupClass()
1576                 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1577                 || (ALLOW_NESTMATE_ACCESS &&
1578                     VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1579                 return false;
1580             return true;
1581         }
1582         private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
1583             assert(!method.isStatic());
1584             // receiver type of mh is too wide; narrow to caller
1585             if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1586                 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1587             }
1588             MethodType rawType = mh.type();
1589             if (rawType.parameterType(0) == caller)  return mh;
1590             MethodType narrowType = rawType.changeParameterType(0, caller);
1591             assert(!mh.isVarargsCollector());  // viewAsType will lose varargs-ness
1592             assert(mh.viewAsTypeChecks(narrowType, true));
1593             assert(mh instanceof DirectMethodHandle);  // DirectMethodHandle.copyWith
1594             return mh.copyWith(narrowType, mh.form);
1595         }
1596 
1597         /** Check access and get the requested method. */
1598         private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1599             final boolean doRestrict    = true;
1600             final boolean checkSecurity = true;
1601             return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1602         }
1603         /** Check access and get the requested method, eliding receiver narrowing rules. */
1604         private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1605             final boolean doRestrict    = false;
1606             final boolean checkSecurity = true;
1607             return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1608         }
1609         /** Check access and get the requested method, eliding security manager checks. */
1610         private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1611             final boolean doRestrict    = true;
1612             final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
1613             return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1614         }
1615         /** Common code for all methods; do not call directly except from immediately above. */
1616         private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1617                                                    boolean checkSecurity,
1618                                                    boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1619             checkMethod(refKind, refc, method);
1620             // Optionally check with the security manager; this isn't needed for unreflect* calls.
1621             if (checkSecurity)
1622                 checkSecurityManager(refc, method);
1623             assert(!method.isMethodHandleInvoke());
1624 
1625             if (refKind == REF_invokeSpecial &&
1626                 refc != lookupClass() &&
1627                 !refc.isInterface() &&
1628                 refc != lookupClass().getSuperclass() &&
1629                 refc.isAssignableFrom(lookupClass())) {
1630                 assert(!method.getName().equals("<init>"));  // not this code path
1631                 // Per JVMS 6.5, desc. of invokespecial instruction:
1632                 // If the method is in a superclass of the LC,
1633                 // and if our original search was above LC.super,
1634                 // repeat the search (symbolic lookup) from LC.super
1635                 // and continue with the direct superclass of that class,
1636                 // and so forth, until a match is found or no further superclasses exist.
1637                 // FIXME: MemberName.resolve should handle this instead.
1638                 Class<?> refcAsSuper = lookupClass();
1639                 MemberName m2;
1640                 do {
1641                     refcAsSuper = refcAsSuper.getSuperclass();
1642                     m2 = new MemberName(refcAsSuper,
1643                                         method.getName(),
1644                                         method.getMethodType(),
1645                                         REF_invokeSpecial);
1646                     m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1647                 } while (m2 == null &&         // no method is found yet
1648                          refc != refcAsSuper); // search up to refc
1649                 if (m2 == null)  throw new InternalError(method.toString());
1650                 method = m2;
1651                 refc = refcAsSuper;
1652                 // redo basic checks
1653                 checkMethod(refKind, refc, method);
1654             }
1655 
1656             MethodHandle mh = DirectMethodHandle.make(refKind, refc, method);
1657             mh = maybeBindCaller(method, mh, callerClass);
1658             mh = mh.setVarargs(method);
1659             // Optionally narrow the receiver argument to refc using restrictReceiver.
1660             if (doRestrict &&
1661                    (refKind == REF_invokeSpecial ||
1662                        (MethodHandleNatives.refKindHasReceiver(refKind) &&
1663                            restrictProtectedReceiver(method))))
1664                 mh = restrictReceiver(method, mh, lookupClass());
1665             return mh;
1666         }
1667         private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1668                                              Class<?> callerClass)
1669                                              throws IllegalAccessException {
1670             if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1671                 return mh;
1672             Class<?> hostClass = lookupClass;
1673             if (!hasPrivateAccess())  // caller must have private access
1674                 hostClass = callerClass;  // callerClass came from a security manager style stack walk
1675             MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1676             // Note: caller will apply varargs after this step happens.
1677             return cbmh;
1678         }
1679         /** Check access and get the requested field. */
1680         private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1681             final boolean checkSecurity = true;
1682             return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1683         }
1684         /** Check access and get the requested field, eliding security manager checks. */
1685         private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1686             final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
1687             return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1688         }
1689         /** Common code for all fields; do not call directly except from immediately above. */
1690         private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
1691                                                   boolean checkSecurity) throws IllegalAccessException {
1692             checkField(refKind, refc, field);
1693             // Optionally check with the security manager; this isn't needed for unreflect* calls.
1694             if (checkSecurity)
1695                 checkSecurityManager(refc, field);
1696             MethodHandle mh = DirectMethodHandle.make(refc, field);
1697             boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
1698                                     restrictProtectedReceiver(field));
1699             if (doRestrict)
1700                 mh = restrictReceiver(field, mh, lookupClass());
1701             return mh;
1702         }
1703         /** Check access and get the requested constructor. */
1704         private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1705             final boolean checkSecurity = true;
1706             return getDirectConstructorCommon(refc, ctor, checkSecurity);
1707         }
1708         /** Check access and get the requested constructor, eliding security manager checks. */
1709         private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
1710             final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
1711             return getDirectConstructorCommon(refc, ctor, checkSecurity);
1712         }
1713         /** Common code for all constructors; do not call directly except from immediately above. */
1714         private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
1715                                                   boolean checkSecurity) throws IllegalAccessException {
1716             assert(ctor.isConstructor());
1717             checkAccess(REF_newInvokeSpecial, refc, ctor);
1718             // Optionally check with the security manager; this isn't needed for unreflect* calls.
1719             if (checkSecurity)
1720                 checkSecurityManager(refc, ctor);
1721             assert(!MethodHandleNatives.isCallerSensitive(ctor));  // maybeBindCaller not relevant here
1722             return DirectMethodHandle.make(ctor).setVarargs(ctor);
1723         }
1724 
1725         /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
1726          */
1727         /*non-public*/
1728         MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
1729             if (!(type instanceof Class || type instanceof MethodType))
1730                 throw new InternalError("unresolved MemberName");
1731             MemberName member = new MemberName(refKind, defc, name, type);
1732             MethodHandle mh = LOOKASIDE_TABLE.get(member);
1733             if (mh != null) {
1734                 checkSymbolicClass(defc);
1735                 return mh;
1736             }
1737             // Treat MethodHandle.invoke and invokeExact specially.
1738             if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
1739                 mh = findVirtualForMH(member.getName(), member.getMethodType());
1740                 if (mh != null) {
1741                     return mh;
1742                 }
1743             }
1744             MemberName resolved = resolveOrFail(refKind, member);
1745             mh = getDirectMethodForConstant(refKind, defc, resolved);
1746             if (mh instanceof DirectMethodHandle
1747                     && canBeCached(refKind, defc, resolved)) {
1748                 MemberName key = mh.internalMemberName();
1749                 if (key != null) {
1750                     key = key.asNormalOriginal();
1751                 }
1752                 if (member.equals(key)) {  // better safe than sorry
1753                     LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
1754                 }
1755             }
1756             return mh;
1757         }
1758         private
1759         boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
1760             if (refKind == REF_invokeSpecial) {
1761                 return false;
1762             }
1763             if (!Modifier.isPublic(defc.getModifiers()) ||
1764                     !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
1765                     !member.isPublic() ||
1766                     member.isCallerSensitive()) {
1767                 return false;
1768             }
1769             ClassLoader loader = defc.getClassLoader();
1770             if (!sun.misc.VM.isSystemDomainLoader(loader)) {
1771                 ClassLoader sysl = ClassLoader.getSystemClassLoader();
1772                 boolean found = false;
1773                 while (sysl != null) {
1774                     if (loader == sysl) { found = true; break; }
1775                     sysl = sysl.getParent();
1776                 }
1777                 if (!found) {
1778                     return false;
1779                 }
1780             }
1781             try {
1782                 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
1783                     new MemberName(refKind, defc, member.getName(), member.getType()));
1784                 checkSecurityManager(defc, resolved2);
1785             } catch (ReflectiveOperationException | SecurityException ex) {
1786                 return false;
1787             }
1788             return true;
1789         }
1790         private
1791         MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
1792                 throws ReflectiveOperationException {
1793             if (MethodHandleNatives.refKindIsField(refKind)) {
1794                 return getDirectFieldNoSecurityManager(refKind, defc, member);
1795             } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
1796                 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
1797             } else if (refKind == REF_newInvokeSpecial) {
1798                 return getDirectConstructorNoSecurityManager(defc, member);
1799             }
1800             // oops
1801             throw newIllegalArgumentException("bad MethodHandle constant #"+member);
1802         }
1803 
1804         static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
1805     }
1806 
1807     /**
1808      * Produces a method handle giving read access to elements of an array.
1809      * The type of the method handle will have a return type of the array's
1810      * element type.  Its first argument will be the array type,
1811      * and the second will be {@code int}.
1812      * @param arrayClass an array type
1813      * @return a method handle which can load values from the given array type
1814      * @throws NullPointerException if the argument is null
1815      * @throws  IllegalArgumentException if arrayClass is not an array type
1816      */
1817     public static
1818     MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
1819         return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
1820     }
1821 
1822     /**
1823      * Produces a method handle giving write access to elements of an array.
1824      * The type of the method handle will have a void return type.
1825      * Its last argument will be the array's element type.
1826      * The first and second arguments will be the array type and int.
1827      * @param arrayClass the class of an array
1828      * @return a method handle which can store values into the array type
1829      * @throws NullPointerException if the argument is null
1830      * @throws IllegalArgumentException if arrayClass is not an array type
1831      */
1832     public static
1833     MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
1834         return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
1835     }
1836 
1837     /// method handle invocation (reflective style)
1838 
1839     /**
1840      * Produces a method handle which will invoke any method handle of the
1841      * given {@code type}, with a given number of trailing arguments replaced by
1842      * a single trailing {@code Object[]} array.
1843      * The resulting invoker will be a method handle with the following
1844      * arguments:
1845      * <ul>
1846      * <li>a single {@code MethodHandle} target
1847      * <li>zero or more leading values (counted by {@code leadingArgCount})
1848      * <li>an {@code Object[]} array containing trailing arguments
1849      * </ul>
1850      * <p>
1851      * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
1852      * the indicated {@code type}.
1853      * That is, if the target is exactly of the given {@code type}, it will behave
1854      * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
1855      * is used to convert the target to the required {@code type}.
1856      * <p>
1857      * The type of the returned invoker will not be the given {@code type}, but rather
1858      * will have all parameters except the first {@code leadingArgCount}
1859      * replaced by a single array of type {@code Object[]}, which will be
1860      * the final parameter.
1861      * <p>
1862      * Before invoking its target, the invoker will spread the final array, apply
1863      * reference casts as necessary, and unbox and widen primitive arguments.
1864      * If, when the invoker is called, the supplied array argument does
1865      * not have the correct number of elements, the invoker will throw
1866      * an {@link IllegalArgumentException} instead of invoking the target.
1867      * <p>
1868      * This method is equivalent to the following code (though it may be more efficient):
1869      * <blockquote><pre>{@code
1870 MethodHandle invoker = MethodHandles.invoker(type);
1871 int spreadArgCount = type.parameterCount() - leadingArgCount;
1872 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
1873 return invoker;
1874      * }</pre></blockquote>
1875      * This method throws no reflective or security exceptions.
1876      * @param type the desired target type
1877      * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
1878      * @return a method handle suitable for invoking any method handle of the given type
1879      * @throws NullPointerException if {@code type} is null
1880      * @throws IllegalArgumentException if {@code leadingArgCount} is not in
1881      *                  the range from 0 to {@code type.parameterCount()} inclusive,
1882      *                  or if the resulting method handle's type would have
1883      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
1884      */
1885     static public
1886     MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
1887         if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
1888             throw newIllegalArgumentException("bad argument count", leadingArgCount);
1889         type = type.asSpreaderType(Object[].class, type.parameterCount() - leadingArgCount);
1890         return type.invokers().spreadInvoker(leadingArgCount);
1891     }
1892 
1893     /**
1894      * Produces a special <em>invoker method handle</em> which can be used to
1895      * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
1896      * The resulting invoker will have a type which is
1897      * exactly equal to the desired type, except that it will accept
1898      * an additional leading argument of type {@code MethodHandle}.
1899      * <p>
1900      * This method is equivalent to the following code (though it may be more efficient):
1901      * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
1902      *
1903      * <p style="font-size:smaller;">
1904      * <em>Discussion:</em>
1905      * Invoker method handles can be useful when working with variable method handles
1906      * of unknown types.
1907      * For example, to emulate an {@code invokeExact} call to a variable method
1908      * handle {@code M}, extract its type {@code T},
1909      * look up the invoker method {@code X} for {@code T},
1910      * and call the invoker method, as {@code X.invoke(T, A...)}.
1911      * (It would not work to call {@code X.invokeExact}, since the type {@code T}
1912      * is unknown.)
1913      * If spreading, collecting, or other argument transformations are required,
1914      * they can be applied once to the invoker {@code X} and reused on many {@code M}
1915      * method handle values, as long as they are compatible with the type of {@code X}.
1916      * <p style="font-size:smaller;">
1917      * <em>(Note:  The invoker method is not available via the Core Reflection API.
1918      * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1919      * on the declared {@code invokeExact} or {@code invoke} method will raise an
1920      * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1921      * <p>
1922      * This method throws no reflective or security exceptions.
1923      * @param type the desired target type
1924      * @return a method handle suitable for invoking any method handle of the given type
1925      * @throws IllegalArgumentException if the resulting method handle's type would have
1926      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
1927      */
1928     static public
1929     MethodHandle exactInvoker(MethodType type) {
1930         return type.invokers().exactInvoker();
1931     }
1932 
1933     /**
1934      * Produces a special <em>invoker method handle</em> which can be used to
1935      * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
1936      * The resulting invoker will have a type which is
1937      * exactly equal to the desired type, except that it will accept
1938      * an additional leading argument of type {@code MethodHandle}.
1939      * <p>
1940      * Before invoking its target, if the target differs from the expected type,
1941      * the invoker will apply reference casts as
1942      * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
1943      * Similarly, the return value will be converted as necessary.
1944      * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
1945      * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
1946      * <p>
1947      * This method is equivalent to the following code (though it may be more efficient):
1948      * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
1949      * <p style="font-size:smaller;">
1950      * <em>Discussion:</em>
1951      * A {@linkplain MethodType#genericMethodType general method type} is one which
1952      * mentions only {@code Object} arguments and return values.
1953      * An invoker for such a type is capable of calling any method handle
1954      * of the same arity as the general type.
1955      * <p style="font-size:smaller;">
1956      * <em>(Note:  The invoker method is not available via the Core Reflection API.
1957      * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
1958      * on the declared {@code invokeExact} or {@code invoke} method will raise an
1959      * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
1960      * <p>
1961      * This method throws no reflective or security exceptions.
1962      * @param type the desired target type
1963      * @return a method handle suitable for invoking any method handle convertible to the given type
1964      * @throws IllegalArgumentException if the resulting method handle's type would have
1965      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
1966      */
1967     static public
1968     MethodHandle invoker(MethodType type) {
1969         return type.invokers().genericInvoker();
1970     }
1971 
1972     static /*non-public*/
1973     MethodHandle basicInvoker(MethodType type) {
1974         return type.invokers().basicInvoker();
1975     }
1976 
1977      /// method handle modification (creation from other method handles)
1978 
1979     /**
1980      * Produces a method handle which adapts the type of the
1981      * given method handle to a new type by pairwise argument and return type conversion.
1982      * The original type and new type must have the same number of arguments.
1983      * The resulting method handle is guaranteed to report a type
1984      * which is equal to the desired new type.
1985      * <p>
1986      * If the original type and new type are equal, returns target.
1987      * <p>
1988      * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
1989      * and some additional conversions are also applied if those conversions fail.
1990      * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
1991      * if possible, before or instead of any conversions done by {@code asType}:
1992      * <ul>
1993      * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
1994      *     then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
1995      *     (This treatment of interfaces follows the usage of the bytecode verifier.)
1996      * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
1997      *     the boolean is converted to a byte value, 1 for true, 0 for false.
1998      *     (This treatment follows the usage of the bytecode verifier.)
1999      * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2000      *     <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2001      *     and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2002      * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2003      *     then a Java casting conversion (JLS 5.5) is applied.
2004      *     (Specifically, <em>T0</em> will convert to <em>T1</em> by
2005      *     widening and/or narrowing.)
2006      * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2007      *     conversion will be applied at runtime, possibly followed
2008      *     by a Java casting conversion (JLS 5.5) on the primitive value,
2009      *     possibly followed by a conversion from byte to boolean by testing
2010      *     the low-order bit.
2011      * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2012      *     and if the reference is null at runtime, a zero value is introduced.
2013      * </ul>
2014      * @param target the method handle to invoke after arguments are retyped
2015      * @param newType the expected type of the new method handle
2016      * @return a method handle which delegates to the target after performing
2017      *           any necessary argument conversions, and arranges for any
2018      *           necessary return value conversions
2019      * @throws NullPointerException if either argument is null
2020      * @throws WrongMethodTypeException if the conversion cannot be made
2021      * @see MethodHandle#asType
2022      */
2023     public static
2024     MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2025         if (!target.type().isCastableTo(newType)) {
2026             throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
2027         }
2028         return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
2029     }
2030 
2031     /**
2032      * Produces a method handle which adapts the calling sequence of the
2033      * given method handle to a new type, by reordering the arguments.
2034      * The resulting method handle is guaranteed to report a type
2035      * which is equal to the desired new type.
2036      * <p>
2037      * The given array controls the reordering.
2038      * Call {@code #I} the number of incoming parameters (the value
2039      * {@code newType.parameterCount()}, and call {@code #O} the number
2040      * of outgoing parameters (the value {@code target.type().parameterCount()}).
2041      * Then the length of the reordering array must be {@code #O},
2042      * and each element must be a non-negative number less than {@code #I}.
2043      * For every {@code N} less than {@code #O}, the {@code N}-th
2044      * outgoing argument will be taken from the {@code I}-th incoming
2045      * argument, where {@code I} is {@code reorder[N]}.
2046      * <p>
2047      * No argument or return value conversions are applied.
2048      * The type of each incoming argument, as determined by {@code newType},
2049      * must be identical to the type of the corresponding outgoing parameter
2050      * or parameters in the target method handle.
2051      * The return type of {@code newType} must be identical to the return
2052      * type of the original target.
2053      * <p>
2054      * The reordering array need not specify an actual permutation.
2055      * An incoming argument will be duplicated if its index appears
2056      * more than once in the array, and an incoming argument will be dropped
2057      * if its index does not appear in the array.
2058      * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2059      * incoming arguments which are not mentioned in the reordering array
2060      * are may be any type, as determined only by {@code newType}.
2061      * <blockquote><pre>{@code
2062 import static java.lang.invoke.MethodHandles.*;
2063 import static java.lang.invoke.MethodType.*;
2064 ...
2065 MethodType intfn1 = methodType(int.class, int.class);
2066 MethodType intfn2 = methodType(int.class, int.class, int.class);
2067 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2068 assert(sub.type().equals(intfn2));
2069 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2070 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2071 assert((int)rsub.invokeExact(1, 100) == 99);
2072 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2073 assert(add.type().equals(intfn2));
2074 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2075 assert(twice.type().equals(intfn1));
2076 assert((int)twice.invokeExact(21) == 42);
2077      * }</pre></blockquote>
2078      * @param target the method handle to invoke after arguments are reordered
2079      * @param newType the expected type of the new method handle
2080      * @param reorder an index array which controls the reordering
2081      * @return a method handle which delegates to the target after it
2082      *           drops unused arguments and moves and/or duplicates the other arguments
2083      * @throws NullPointerException if any argument is null
2084      * @throws IllegalArgumentException if the index array length is not equal to
2085      *                  the arity of the target, or if any index array element
2086      *                  not a valid index for a parameter of {@code newType},
2087      *                  or if two corresponding parameter types in
2088      *                  {@code target.type()} and {@code newType} are not identical,
2089      */
2090     public static
2091     MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2092         reorder = reorder.clone();
2093         permuteArgumentChecks(reorder, newType, target.type());
2094         // first detect dropped arguments and handle them separately
2095         MethodHandle originalTarget = target;
2096         int newArity = newType.parameterCount();
2097         for (int dropIdx; (dropIdx = findFirstDrop(reorder, newArity)) >= 0; ) {
2098             // dropIdx is missing from reorder; add it in at the end
2099             int oldArity = reorder.length;
2100             target = dropArguments(target, oldArity, newType.parameterType(dropIdx));
2101             reorder = Arrays.copyOf(reorder, oldArity+1);
2102             reorder[oldArity] = dropIdx;
2103         }
2104         assert(target == originalTarget || permuteArgumentChecks(reorder, newType, target.type()));
2105         // Note:  This may cache too many distinct LFs. Consider backing off to varargs code.
2106         BoundMethodHandle result = target.rebind();
2107         LambdaForm form = result.form.permuteArguments(1, reorder, basicTypes(newType.parameterList()));
2108         return result.copyWith(newType, form);
2109     }
2110 
2111     /** Return the first value in [0..newArity-1] that is not present in reorder. */
2112     private static int findFirstDrop(int[] reorder, int newArity) {
2113         final int BIT_LIMIT = 63;  // max number of bits in bit mask
2114         if (newArity < BIT_LIMIT) {
2115             long mask = 0;
2116             for (int arg : reorder) {
2117                 assert(arg < newArity);
2118                 mask |= (1 << arg);
2119             }
2120             if (mask == (1 << newArity) - 1) {
2121                 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2122                 return -1;
2123             }
2124             // find first zero
2125             long zeroBit = Long.lowestOneBit(~mask);
2126             int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2127             assert(zeroPos < newArity);
2128             return zeroPos;
2129         }
2130         BitSet mask = new BitSet(newArity);
2131         for (int arg : reorder) {
2132             assert(arg < newArity);
2133             mask.set(arg);
2134         }
2135         int zeroPos = mask.nextClearBit(0);
2136         if (zeroPos == newArity)
2137             return -1;
2138         return zeroPos;
2139     }
2140 
2141     private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2142         if (newType.returnType() != oldType.returnType())
2143             throw newIllegalArgumentException("return types do not match",
2144                     oldType, newType);
2145         if (reorder.length == oldType.parameterCount()) {
2146             int limit = newType.parameterCount();
2147             boolean bad = false;
2148             for (int j = 0; j < reorder.length; j++) {
2149                 int i = reorder[j];
2150                 if (i < 0 || i >= limit) {
2151                     bad = true; break;
2152                 }
2153                 Class<?> src = newType.parameterType(i);
2154                 Class<?> dst = oldType.parameterType(j);
2155                 if (src != dst)
2156                     throw newIllegalArgumentException("parameter types do not match after reorder",
2157                             oldType, newType);
2158             }
2159             if (!bad)  return true;
2160         }
2161         throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2162     }
2163 
2164     /**
2165      * Produces a method handle of the requested return type which returns the given
2166      * constant value every time it is invoked.
2167      * <p>
2168      * Before the method handle is returned, the passed-in value is converted to the requested type.
2169      * If the requested type is primitive, widening primitive conversions are attempted,
2170      * else reference conversions are attempted.
2171      * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2172      * @param type the return type of the desired method handle
2173      * @param value the value to return
2174      * @return a method handle of the given return type and no arguments, which always returns the given value
2175      * @throws NullPointerException if the {@code type} argument is null
2176      * @throws ClassCastException if the value cannot be converted to the required return type
2177      * @throws IllegalArgumentException if the given type is {@code void.class}
2178      */
2179     public static
2180     MethodHandle constant(Class<?> type, Object value) {
2181         if (type.isPrimitive()) {
2182             if (type == void.class)
2183                 throw newIllegalArgumentException("void type");
2184             Wrapper w = Wrapper.forPrimitiveType(type);
2185             return insertArguments(identity(type), 0, w.convert(value, type));
2186         } else {
2187             return identity(type).bindTo(type.cast(value));
2188         }
2189     }
2190 
2191     /**
2192      * Produces a method handle which returns its sole argument when invoked.
2193      * @param type the type of the sole parameter and return value of the desired method handle
2194      * @return a unary method handle which accepts and returns the given type
2195      * @throws NullPointerException if the argument is null
2196      * @throws IllegalArgumentException if the given type is {@code void.class}
2197      */
2198     public static
2199     MethodHandle identity(Class<?> type) {
2200         if (type == void.class)
2201             throw newIllegalArgumentException("void type");
2202         else if (type == Object.class)
2203             return ValueConversions.identity();
2204         else if (type.isPrimitive())
2205             return ValueConversions.identity(Wrapper.forPrimitiveType(type));
2206         else
2207             return MethodHandleImpl.makeReferenceIdentity(type);
2208     }
2209 
2210     /**
2211      * Provides a target method handle with one or more <em>bound arguments</em>
2212      * in advance of the method handle's invocation.
2213      * The formal parameters to the target corresponding to the bound
2214      * arguments are called <em>bound parameters</em>.
2215      * Returns a new method handle which saves away the bound arguments.
2216      * When it is invoked, it receives arguments for any non-bound parameters,
2217      * binds the saved arguments to their corresponding parameters,
2218      * and calls the original target.
2219      * <p>
2220      * The type of the new method handle will drop the types for the bound
2221      * parameters from the original target type, since the new method handle
2222      * will no longer require those arguments to be supplied by its callers.
2223      * <p>
2224      * Each given argument object must match the corresponding bound parameter type.
2225      * If a bound parameter type is a primitive, the argument object
2226      * must be a wrapper, and will be unboxed to produce the primitive value.
2227      * <p>
2228      * The {@code pos} argument selects which parameters are to be bound.
2229      * It may range between zero and <i>N-L</i> (inclusively),
2230      * where <i>N</i> is the arity of the target method handle
2231      * and <i>L</i> is the length of the values array.
2232      * @param target the method handle to invoke after the argument is inserted
2233      * @param pos where to insert the argument (zero for the first)
2234      * @param values the series of arguments to insert
2235      * @return a method handle which inserts an additional argument,
2236      *         before calling the original method handle
2237      * @throws NullPointerException if the target or the {@code values} array is null
2238      * @see MethodHandle#bindTo
2239      */
2240     public static
2241     MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
2242         int insCount = values.length;
2243         Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
2244         if (insCount == 0)  return target;
2245         BoundMethodHandle result = target.rebind();
2246         for (int i = 0; i < insCount; i++) {
2247             Object value = values[i];
2248             Class<?> ptype = ptypes[pos+i];
2249             if (ptype.isPrimitive()) {
2250                 result = insertArgumentPrimitive(result, pos, ptype, value);
2251             } else {
2252                 value = ptype.cast(value);  // throw CCE if needed
2253                 result = result.bindArgumentL(pos, value);
2254             }
2255         }
2256         return result;
2257     }
2258 
2259     private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
2260                                                              Class<?> ptype, Object value) {
2261         Wrapper w = Wrapper.forPrimitiveType(ptype);
2262         // perform unboxing and/or primitive conversion
2263         value = w.convert(value, ptype);
2264         switch (w) {
2265         case INT:     return result.bindArgumentI(pos, (int)value);
2266         case LONG:    return result.bindArgumentJ(pos, (long)value);
2267         case FLOAT:   return result.bindArgumentF(pos, (float)value);
2268         case DOUBLE:  return result.bindArgumentD(pos, (double)value);
2269         default:      return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
2270         }
2271     }
2272 
2273     private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
2274         MethodType oldType = target.type();
2275         int outargs = oldType.parameterCount();
2276         int inargs  = outargs - insCount;
2277         if (inargs < 0)
2278             throw newIllegalArgumentException("too many values to insert");
2279         if (pos < 0 || pos > inargs)
2280             throw newIllegalArgumentException("no argument type to append");
2281         return oldType.ptypes();
2282     }
2283 
2284     /**
2285      * Produces a method handle which will discard some dummy arguments
2286      * before calling some other specified <i>target</i> method handle.
2287      * The type of the new method handle will be the same as the target's type,
2288      * except it will also include the dummy argument types,
2289      * at some given position.
2290      * <p>
2291      * The {@code pos} argument may range between zero and <i>N</i>,
2292      * where <i>N</i> is the arity of the target.
2293      * If {@code pos} is zero, the dummy arguments will precede
2294      * the target's real arguments; if {@code pos} is <i>N</i>
2295      * they will come after.
2296      * <p>
2297      * <b>Example:</b>
2298      * <blockquote><pre>{@code
2299 import static java.lang.invoke.MethodHandles.*;
2300 import static java.lang.invoke.MethodType.*;
2301 ...
2302 MethodHandle cat = lookup().findVirtual(String.class,
2303   "concat", methodType(String.class, String.class));
2304 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2305 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
2306 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
2307 assertEquals(bigType, d0.type());
2308 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
2309      * }</pre></blockquote>
2310      * <p>
2311      * This method is also equivalent to the following code:
2312      * <blockquote><pre>
2313      * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
2314      * </pre></blockquote>
2315      * @param target the method handle to invoke after the arguments are dropped
2316      * @param valueTypes the type(s) of the argument(s) to drop
2317      * @param pos position of first argument to drop (zero for the leftmost)
2318      * @return a method handle which drops arguments of the given types,
2319      *         before calling the original method handle
2320      * @throws NullPointerException if the target is null,
2321      *                              or if the {@code valueTypes} list or any of its elements is null
2322      * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2323      *                  or if {@code pos} is negative or greater than the arity of the target,
2324      *                  or if the new method handle's type would have too many parameters
2325      */
2326     public static
2327     MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
2328         MethodType oldType = target.type();  // get NPE
2329         int dropped = dropArgumentChecks(oldType, pos, valueTypes);
2330         if (dropped == 0)  return target;
2331         BoundMethodHandle result = target.rebind();
2332         LambdaForm lform = result.form;
2333         lform = lform.addArguments(pos, valueTypes);
2334         MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
2335         result = result.copyWith(newType, lform);
2336         return result;
2337     }
2338 
2339     private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
2340         int dropped = valueTypes.size();
2341         MethodType.checkSlotCount(dropped);
2342         int outargs = oldType.parameterCount();
2343         int inargs  = outargs + dropped;
2344         if (pos < 0 || pos > outargs)
2345             throw newIllegalArgumentException("no argument type to remove"
2346                     + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
2347                     );
2348         return dropped;
2349     }
2350 
2351     /**
2352      * Produces a method handle which will discard some dummy arguments
2353      * before calling some other specified <i>target</i> method handle.
2354      * The type of the new method handle will be the same as the target's type,
2355      * except it will also include the dummy argument types,
2356      * at some given position.
2357      * <p>
2358      * The {@code pos} argument may range between zero and <i>N</i>,
2359      * where <i>N</i> is the arity of the target.
2360      * If {@code pos} is zero, the dummy arguments will precede
2361      * the target's real arguments; if {@code pos} is <i>N</i>
2362      * they will come after.
2363      * <p>
2364      * <b>Example:</b>
2365      * <blockquote><pre>{@code
2366 import static java.lang.invoke.MethodHandles.*;
2367 import static java.lang.invoke.MethodType.*;
2368 ...
2369 MethodHandle cat = lookup().findVirtual(String.class,
2370   "concat", methodType(String.class, String.class));
2371 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2372 MethodHandle d0 = dropArguments(cat, 0, String.class);
2373 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
2374 MethodHandle d1 = dropArguments(cat, 1, String.class);
2375 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
2376 MethodHandle d2 = dropArguments(cat, 2, String.class);
2377 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
2378 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
2379 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
2380      * }</pre></blockquote>
2381      * <p>
2382      * This method is also equivalent to the following code:
2383      * <blockquote><pre>
2384      * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
2385      * </pre></blockquote>
2386      * @param target the method handle to invoke after the arguments are dropped
2387      * @param valueTypes the type(s) of the argument(s) to drop
2388      * @param pos position of first argument to drop (zero for the leftmost)
2389      * @return a method handle which drops arguments of the given types,
2390      *         before calling the original method handle
2391      * @throws NullPointerException if the target is null,
2392      *                              or if the {@code valueTypes} array or any of its elements is null
2393      * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
2394      *                  or if {@code pos} is negative or greater than the arity of the target,
2395      *                  or if the new method handle's type would have
2396      *                  <a href="MethodHandle.html#maxarity">too many parameters</a>
2397      */
2398     public static
2399     MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
2400         return dropArguments(target, pos, Arrays.asList(valueTypes));
2401     }
2402 
2403     /**
2404      * Adapts a target method handle by pre-processing
2405      * one or more of its arguments, each with its own unary filter function,
2406      * and then calling the target with each pre-processed argument
2407      * replaced by the result of its corresponding filter function.
2408      * <p>
2409      * The pre-processing is performed by one or more method handles,
2410      * specified in the elements of the {@code filters} array.
2411      * The first element of the filter array corresponds to the {@code pos}
2412      * argument of the target, and so on in sequence.
2413      * <p>
2414      * Null arguments in the array are treated as identity functions,
2415      * and the corresponding arguments left unchanged.
2416      * (If there are no non-null elements in the array, the original target is returned.)
2417      * Each filter is applied to the corresponding argument of the adapter.
2418      * <p>
2419      * If a filter {@code F} applies to the {@code N}th argument of
2420      * the target, then {@code F} must be a method handle which
2421      * takes exactly one argument.  The type of {@code F}'s sole argument
2422      * replaces the corresponding argument type of the target
2423      * in the resulting adapted method handle.
2424      * The return type of {@code F} must be identical to the corresponding
2425      * parameter type of the target.
2426      * <p>
2427      * It is an error if there are elements of {@code filters}
2428      * (null or not)
2429      * which do not correspond to argument positions in the target.
2430      * <p><b>Example:</b>
2431      * <blockquote><pre>{@code
2432 import static java.lang.invoke.MethodHandles.*;
2433 import static java.lang.invoke.MethodType.*;
2434 ...
2435 MethodHandle cat = lookup().findVirtual(String.class,
2436   "concat", methodType(String.class, String.class));
2437 MethodHandle upcase = lookup().findVirtual(String.class,
2438   "toUpperCase", methodType(String.class));
2439 assertEquals("xy", (String) cat.invokeExact("x", "y"));
2440 MethodHandle f0 = filterArguments(cat, 0, upcase);
2441 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
2442 MethodHandle f1 = filterArguments(cat, 1, upcase);
2443 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
2444 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
2445 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
2446      * }</pre></blockquote>
2447      * <p> Here is pseudocode for the resulting adapter:
2448      * <blockquote><pre>{@code
2449      * V target(P... p, A[i]... a[i], B... b);
2450      * A[i] filter[i](V[i]);
2451      * T adapter(P... p, V[i]... v[i], B... b) {
2452      *   return target(p..., f[i](v[i])..., b...);
2453      * }
2454      * }</pre></blockquote>
2455      *
2456      * @param target the method handle to invoke after arguments are filtered
2457      * @param pos the position of the first argument to filter
2458      * @param filters method handles to call initially on filtered arguments
2459      * @return method handle which incorporates the specified argument filtering logic
2460      * @throws NullPointerException if the target is null
2461      *                              or if the {@code filters} array is null
2462      * @throws IllegalArgumentException if a non-null element of {@code filters}
2463      *          does not match a corresponding argument type of target as described above,
2464      *          or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
2465      *          or if the resulting method handle's type would have
2466      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
2467      */
2468     public static
2469     MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
2470         MethodType targetType = target.type();
2471         MethodHandle adapter = target;
2472         MethodType adapterType = null;
2473         assert((adapterType = targetType) != null);
2474         int maxPos = targetType.parameterCount();
2475         if (pos + filters.length > maxPos)
2476             throw newIllegalArgumentException("too many filters");
2477         int curPos = pos-1;  // pre-incremented
2478         for (MethodHandle filter : filters) {
2479             curPos += 1;
2480             if (filter == null)  continue;  // ignore null elements of filters
2481             adapter = filterArgument(adapter, curPos, filter);
2482             assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
2483         }
2484         assert(adapterType.equals(adapter.type()));
2485         return adapter;
2486     }
2487 
2488     /*non-public*/ static
2489     MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
2490         MethodType targetType = target.type();
2491         MethodType filterType = filter.type();
2492         if (filterType.parameterCount() != 1
2493             || filterType.returnType() != targetType.parameterType(pos))
2494             throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2495         return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2496     }
2497 
2498     /**
2499      * Adapts a target method handle by pre-processing
2500      * a sub-sequence of its arguments with a filter (another method handle).
2501      * The pre-processed arguments are replaced by the result (if any) of the
2502      * filter function.
2503      * The target is then called on the modified (usually shortened) argument list.
2504      * <p>
2505      * If the filter returns a value, the target must accept that value as
2506      * its argument in position {@code pos}, preceded and/or followed by
2507      * any arguments not passed to the filter.
2508      * If the filter returns void, the target must accept all arguments
2509      * not passed to the filter.
2510      * No arguments are reordered, and a result returned from the filter
2511      * replaces (in order) the whole subsequence of arguments originally
2512      * passed to the adapter.
2513      * <p>
2514      * The argument types (if any) of the filter
2515      * replace zero or one argument types of the target, at position {@code pos},
2516      * in the resulting adapted method handle.
2517      * The return type of the filter (if any) must be identical to the
2518      * argument type of the target at position {@code pos}, and that target argument
2519      * is supplied by the return value of the filter.
2520      * <p>
2521      * In all cases, {@code pos} must be greater than or equal to zero, and
2522      * {@code pos} must also be less than or equal to the target's arity.
2523      * <p><b>Example:</b>
2524      * <blockquote><pre>{@code
2525 import static java.lang.invoke.MethodHandles.*;
2526 import static java.lang.invoke.MethodType.*;
2527 ...
2528 MethodHandle deepToString = publicLookup()
2529   .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
2530 
2531 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
2532 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
2533 
2534 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
2535 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
2536 
2537 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
2538 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
2539 assertEquals("[top, [up, down], strange]",
2540              (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
2541 
2542 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
2543 assertEquals("[top, [up, down], [strange]]",
2544              (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
2545 
2546 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
2547 assertEquals("[top, [[up, down, strange], charm], bottom]",
2548              (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
2549      * }</pre></blockquote>
2550      * <p> Here is pseudocode for the resulting adapter:
2551      * <blockquote><pre>{@code
2552      * T target(A...,V,C...);
2553      * V filter(B...);
2554      * T adapter(A... a,B... b,C... c) {
2555      *   V v = filter(b...);
2556      *   return target(a...,v,c...);
2557      * }
2558      * // and if the filter has no arguments:
2559      * T target2(A...,V,C...);
2560      * V filter2();
2561      * T adapter2(A... a,C... c) {
2562      *   V v = filter2();
2563      *   return target2(a...,v,c...);
2564      * }
2565      * // and if the filter has a void return:
2566      * T target3(A...,C...);
2567      * void filter3(B...);
2568      * void adapter3(A... a,B... b,C... c) {
2569      *   filter3(b...);
2570      *   return target3(a...,c...);
2571      * }
2572      * }</pre></blockquote>
2573      * <p>
2574      * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
2575      * one which first "folds" the affected arguments, and then drops them, in separate
2576      * steps as follows:
2577      * <blockquote><pre>{@code
2578      * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
2579      * mh = MethodHandles.foldArguments(mh, coll); //step 1
2580      * }</pre></blockquote>
2581      * If the target method handle consumes no arguments besides than the result
2582      * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
2583      * is equivalent to {@code filterReturnValue(coll, mh)}.
2584      * If the filter method handle {@code coll} consumes one argument and produces
2585      * a non-void result, then {@code collectArguments(mh, N, coll)}
2586      * is equivalent to {@code filterArguments(mh, N, coll)}.
2587      * Other equivalences are possible but would require argument permutation.
2588      *
2589      * @param target the method handle to invoke after filtering the subsequence of arguments
2590      * @param pos the position of the first adapter argument to pass to the filter,
2591      *            and/or the target argument which receives the result of the filter
2592      * @param filter method handle to call on the subsequence of arguments
2593      * @return method handle which incorporates the specified argument subsequence filtering logic
2594      * @throws NullPointerException if either argument is null
2595      * @throws IllegalArgumentException if the return type of {@code filter}
2596      *          is non-void and is not the same as the {@code pos} argument of the target,
2597      *          or if {@code pos} is not between 0 and the target's arity, inclusive,
2598      *          or if the resulting method handle's type would have
2599      *          <a href="MethodHandle.html#maxarity">too many parameters</a>
2600      * @see MethodHandles#foldArguments
2601      * @see MethodHandles#filterArguments
2602      * @see MethodHandles#filterReturnValue
2603      */
2604     public static
2605     MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
2606         MethodType targetType = target.type();
2607         MethodType filterType = filter.type();
2608         if (filterType.returnType() != void.class &&
2609             filterType.returnType() != targetType.parameterType(pos))
2610             throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
2611         return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
2612     }
2613 
2614     /**
2615      * Adapts a target method handle by post-processing
2616      * its return value (if any) with a filter (another method handle).
2617      * The result of the filter is returned from the adapter.
2618      * <p>
2619      * If the target returns a value, the filter must accept that value as
2620      * its only argument.
2621      * If the target returns void, the filter must accept no arguments.
2622      * <p>
2623      * The return type of the filter
2624      * replaces the return type of the target
2625      * in the resulting adapted method handle.
2626      * The argument type of the filter (if any) must be identical to the
2627      * return type of the target.
2628      * <p><b>Example:</b>
2629      * <blockquote><pre>{@code
2630 import static java.lang.invoke.MethodHandles.*;
2631 import static java.lang.invoke.MethodType.*;
2632 ...
2633 MethodHandle cat = lookup().findVirtual(String.class,
2634   "concat", methodType(String.class, String.class));
2635 MethodHandle length = lookup().findVirtual(String.class,
2636   "length", methodType(int.class));
2637 System.out.println((String) cat.invokeExact("x", "y")); // xy
2638 MethodHandle f0 = filterReturnValue(cat, length);
2639 System.out.println((int) f0.invokeExact("x", "y")); // 2
2640      * }</pre></blockquote>
2641      * <p> Here is pseudocode for the resulting adapter:
2642      * <blockquote><pre>{@code
2643      * V target(A...);
2644      * T filter(V);
2645      * T adapter(A... a) {
2646      *   V v = target(a...);
2647      *   return filter(v);
2648      * }
2649      * // and if the target has a void return:
2650      * void target2(A...);
2651      * T filter2();
2652      * T adapter2(A... a) {
2653      *   target2(a...);
2654      *   return filter2();
2655      * }
2656      * // and if the filter has a void return:
2657      * V target3(A...);
2658      * void filter3(V);
2659      * void adapter3(A... a) {
2660      *   V v = target3(a...);
2661      *   filter3(v);
2662      * }
2663      * }</pre></blockquote>
2664      * @param target the method handle to invoke before filtering the return value
2665      * @param filter method handle to call on the return value
2666      * @return method handle which incorporates the specified return value filtering logic
2667      * @throws NullPointerException if either argument is null
2668      * @throws IllegalArgumentException if the argument list of {@code filter}
2669      *          does not match the return type of target as described above
2670      */
2671     public static
2672     MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
2673         MethodType targetType = target.type();
2674         MethodType filterType = filter.type();
2675         Class<?> rtype = targetType.returnType();
2676         int filterValues = filterType.parameterCount();
2677         if (filterValues == 0
2678                 ? (rtype != void.class)
2679                 : (rtype != filterType.parameterType(0)))
2680             throw newIllegalArgumentException("target and filter types do not match", target, filter);
2681         // result = fold( lambda(retval, arg...) { filter(retval) },
2682         //                lambda(        arg...) { target(arg...) } )
2683         return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
2684     }
2685 
2686     /**
2687      * Adapts a target method handle by pre-processing
2688      * some of its arguments, and then calling the target with
2689      * the result of the pre-processing, inserted into the original
2690      * sequence of arguments.
2691      * <p>
2692      * The pre-processing is performed by {@code combiner}, a second method handle.
2693      * Of the arguments passed to the adapter, the first {@code N} arguments
2694      * are copied to the combiner, which is then called.
2695      * (Here, {@code N} is defined as the parameter count of the combiner.)
2696      * After this, control passes to the target, with any result
2697      * from the combiner inserted before the original {@code N} incoming
2698      * arguments.
2699      * <p>
2700      * If the combiner returns a value, the first parameter type of the target
2701      * must be identical with the return type of the combiner, and the next
2702      * {@code N} parameter types of the target must exactly match the parameters
2703      * of the combiner.
2704      * <p>
2705      * If the combiner has a void return, no result will be inserted,
2706      * and the first {@code N} parameter types of the target
2707      * must exactly match the parameters of the combiner.
2708      * <p>
2709      * The resulting adapter is the same type as the target, except that the
2710      * first parameter type is dropped,
2711      * if it corresponds to the result of the combiner.
2712      * <p>
2713      * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
2714      * that either the combiner or the target does not wish to receive.
2715      * If some of the incoming arguments are destined only for the combiner,
2716      * consider using {@link MethodHandle#asCollector asCollector} instead, since those
2717      * arguments will not need to be live on the stack on entry to the
2718      * target.)
2719      * <p><b>Example:</b>
2720      * <blockquote><pre>{@code
2721 import static java.lang.invoke.MethodHandles.*;
2722 import static java.lang.invoke.MethodType.*;
2723 ...
2724 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
2725   "println", methodType(void.class, String.class))
2726     .bindTo(System.out);
2727 MethodHandle cat = lookup().findVirtual(String.class,
2728   "concat", methodType(String.class, String.class));
2729 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
2730 MethodHandle catTrace = foldArguments(cat, trace);
2731 // also prints "boo":
2732 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
2733      * }</pre></blockquote>
2734      * <p> Here is pseudocode for the resulting adapter:
2735      * <blockquote><pre>{@code
2736      * // there are N arguments in A...
2737      * T target(V, A[N]..., B...);
2738      * V combiner(A...);
2739      * T adapter(A... a, B... b) {
2740      *   V v = combiner(a...);
2741      *   return target(v, a..., b...);
2742      * }
2743      * // and if the combiner has a void return:
2744      * T target2(A[N]..., B...);
2745      * void combiner2(A...);
2746      * T adapter2(A... a, B... b) {
2747      *   combiner2(a...);
2748      *   return target2(a..., b...);
2749      * }
2750      * }</pre></blockquote>
2751      * @param target the method handle to invoke after arguments are combined
2752      * @param combiner method handle to call initially on the incoming arguments
2753      * @return method handle which incorporates the specified argument folding logic
2754      * @throws NullPointerException if either argument is null
2755      * @throws IllegalArgumentException if {@code combiner}'s return type
2756      *          is non-void and not the same as the first argument type of
2757      *          the target, or if the initial {@code N} argument types
2758      *          of the target
2759      *          (skipping one matching the {@code combiner}'s return type)
2760      *          are not identical with the argument types of {@code combiner}
2761      */
2762     public static
2763     MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
2764         int pos = 0;
2765         MethodType targetType = target.type();
2766         MethodType combinerType = combiner.type();
2767         int foldPos = pos;
2768         int foldArgs = combinerType.parameterCount();
2769         int foldVals = combinerType.returnType() == void.class ? 0 : 1;
2770         int afterInsertPos = foldPos + foldVals;
2771         boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
2772         if (ok && !(combinerType.parameterList()
2773                     .equals(targetType.parameterList().subList(afterInsertPos,
2774                                                                afterInsertPos + foldArgs))))
2775             ok = false;
2776         if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
2777             ok = false;
2778         if (!ok)
2779             throw misMatchedTypes("target and combiner types", targetType, combinerType);
2780         MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
2781         return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
2782     }
2783 
2784     /**
2785      * Makes a method handle which adapts a target method handle,
2786      * by guarding it with a test, a boolean-valued method handle.
2787      * If the guard fails, a fallback handle is called instead.
2788      * All three method handles must have the same corresponding
2789      * argument and return types, except that the return type
2790      * of the test must be boolean, and the test is allowed
2791      * to have fewer arguments than the other two method handles.
2792      * <p> Here is pseudocode for the resulting adapter:
2793      * <blockquote><pre>{@code
2794      * boolean test(A...);
2795      * T target(A...,B...);
2796      * T fallback(A...,B...);
2797      * T adapter(A... a,B... b) {
2798      *   if (test(a...))
2799      *     return target(a..., b...);
2800      *   else
2801      *     return fallback(a..., b...);
2802      * }
2803      * }</pre></blockquote>
2804      * Note that the test arguments ({@code a...} in the pseudocode) cannot
2805      * be modified by execution of the test, and so are passed unchanged
2806      * from the caller to the target or fallback as appropriate.
2807      * @param test method handle used for test, must return boolean
2808      * @param target method handle to call if test passes
2809      * @param fallback method handle to call if test fails
2810      * @return method handle which incorporates the specified if/then/else logic
2811      * @throws NullPointerException if any argument is null
2812      * @throws IllegalArgumentException if {@code test} does not return boolean,
2813      *          or if all three method types do not match (with the return
2814      *          type of {@code test} changed to match that of the target).
2815      */
2816     public static
2817     MethodHandle guardWithTest(MethodHandle test,
2818                                MethodHandle target,
2819                                MethodHandle fallback) {
2820         MethodType gtype = test.type();
2821         MethodType ttype = target.type();
2822         MethodType ftype = fallback.type();
2823         if (!ttype.equals(ftype))
2824             throw misMatchedTypes("target and fallback types", ttype, ftype);
2825         if (gtype.returnType() != boolean.class)
2826             throw newIllegalArgumentException("guard type is not a predicate "+gtype);
2827         List<Class<?>> targs = ttype.parameterList();
2828         List<Class<?>> gargs = gtype.parameterList();
2829         if (!targs.equals(gargs)) {
2830             int gpc = gargs.size(), tpc = targs.size();
2831             if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
2832                 throw misMatchedTypes("target and test types", ttype, gtype);
2833             test = dropArguments(test, gpc, targs.subList(gpc, tpc));
2834             gtype = test.type();
2835         }
2836         return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
2837     }
2838 
2839     static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
2840         return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
2841     }
2842 
2843     /**
2844      * Makes a method handle which adapts a target method handle,
2845      * by running it inside an exception handler.
2846      * If the target returns normally, the adapter returns that value.
2847      * If an exception matching the specified type is thrown, the fallback
2848      * handle is called instead on the exception, plus the original arguments.
2849      * <p>
2850      * The target and handler must have the same corresponding
2851      * argument and return types, except that handler may omit trailing arguments
2852      * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
2853      * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
2854      * <p> Here is pseudocode for the resulting adapter:
2855      * <blockquote><pre>{@code
2856      * T target(A..., B...);
2857      * T handler(ExType, A...);
2858      * T adapter(A... a, B... b) {
2859      *   try {
2860      *     return target(a..., b...);
2861      *   } catch (ExType ex) {
2862      *     return handler(ex, a...);
2863      *   }
2864      * }
2865      * }</pre></blockquote>
2866      * Note that the saved arguments ({@code a...} in the pseudocode) cannot
2867      * be modified by execution of the target, and so are passed unchanged
2868      * from the caller to the handler, if the handler is invoked.
2869      * <p>
2870      * The target and handler must return the same type, even if the handler
2871      * always throws.  (This might happen, for instance, because the handler
2872      * is simulating a {@code finally} clause).
2873      * To create such a throwing handler, compose the handler creation logic
2874      * with {@link #throwException throwException},
2875      * in order to create a method handle of the correct return type.
2876      * @param target method handle to call
2877      * @param exType the type of exception which the handler will catch
2878      * @param handler method handle to call if a matching exception is thrown
2879      * @return method handle which incorporates the specified try/catch logic
2880      * @throws NullPointerException if any argument is null
2881      * @throws IllegalArgumentException if {@code handler} does not accept
2882      *          the given exception type, or if the method handle types do
2883      *          not match in their return types and their
2884      *          corresponding parameters
2885      */
2886     public static
2887     MethodHandle catchException(MethodHandle target,
2888                                 Class<? extends Throwable> exType,
2889                                 MethodHandle handler) {
2890         MethodType ttype = target.type();
2891         MethodType htype = handler.type();
2892         if (htype.parameterCount() < 1 ||
2893             !htype.parameterType(0).isAssignableFrom(exType))
2894             throw newIllegalArgumentException("handler does not accept exception type "+exType);
2895         if (htype.returnType() != ttype.returnType())
2896             throw misMatchedTypes("target and handler return types", ttype, htype);
2897         List<Class<?>> targs = ttype.parameterList();
2898         List<Class<?>> hargs = htype.parameterList();
2899         hargs = hargs.subList(1, hargs.size());  // omit leading parameter from handler
2900         if (!targs.equals(hargs)) {
2901             int hpc = hargs.size(), tpc = targs.size();
2902             if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
2903                 throw misMatchedTypes("target and handler types", ttype, htype);
2904             handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc));
2905             htype = handler.type();
2906         }
2907         return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
2908     }
2909 
2910     /**
2911      * Produces a method handle which will throw exceptions of the given {@code exType}.
2912      * The method handle will accept a single argument of {@code exType},
2913      * and immediately throw it as an exception.
2914      * The method type will nominally specify a return of {@code returnType}.
2915      * The return type may be anything convenient:  It doesn't matter to the
2916      * method handle's behavior, since it will never return normally.
2917      * @param returnType the return type of the desired method handle
2918      * @param exType the parameter type of the desired method handle
2919      * @return method handle which can throw the given exceptions
2920      * @throws NullPointerException if either argument is null
2921      */
2922     public static
2923     MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
2924         if (!Throwable.class.isAssignableFrom(exType))
2925             throw new ClassCastException(exType.getName());
2926         return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
2927     }
2928 }