1 /*
   2  * Copyright (c) 2008, 2020, 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.constant.ClassDesc;
  29 import java.lang.constant.Constable;
  30 import java.lang.constant.MethodTypeDesc;
  31 import java.lang.ref.Reference;
  32 import java.lang.ref.ReferenceQueue;
  33 import java.lang.ref.WeakReference;
  34 import java.util.Arrays;
  35 import java.util.Collections;
  36 import java.util.List;
  37 import java.util.NoSuchElementException;
  38 import java.util.Objects;
  39 import java.util.Optional;
  40 import java.util.StringJoiner;
  41 import java.util.concurrent.ConcurrentHashMap;
  42 import java.util.concurrent.ConcurrentMap;
  43 import java.util.stream.Stream;
  44 
  45 import jdk.internal.vm.annotation.Stable;
  46 import sun.invoke.util.BytecodeDescriptor;
  47 import sun.invoke.util.VerifyType;
  48 import sun.invoke.util.Wrapper;
  49 import sun.security.util.SecurityConstants;
  50 
  51 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
  52 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
  53 import static java.lang.invoke.MethodType.fromDescriptor;
  54 
  55 /**
  56  * A method type represents the arguments and return type accepted and
  57  * returned by a method handle, or the arguments and return type passed
  58  * and expected  by a method handle caller.  Method types must be properly
  59  * matched between a method handle and all its callers,
  60  * and the JVM's operations enforce this matching at, specifically
  61  * during calls to {@link MethodHandle#invokeExact MethodHandle.invokeExact}
  62  * and {@link MethodHandle#invoke MethodHandle.invoke}, and during execution
  63  * of {@code invokedynamic} instructions.
  64  * <p>
  65  * The structure is a return type accompanied by any number of parameter types.
  66  * The types (primitive, {@code void}, and reference) are represented by {@link Class} objects.
  67  * (For ease of exposition, we treat {@code void} as if it were a type.
  68  * In fact, it denotes the absence of a return type.)
  69  * <p>
  70  * All instances of {@code MethodType} are immutable.
  71  * Two instances are completely interchangeable if they compare equal.
  72  * Equality depends on pairwise correspondence of the return and parameter types and on nothing else.
  73  * <p>
  74  * This type can be created only by factory methods.
  75  * All factory methods may cache values, though caching is not guaranteed.
  76  * Some factory methods are static, while others are virtual methods which
  77  * modify precursor method types, e.g., by changing a selected parameter.
  78  * <p>
  79  * Factory methods which operate on groups of parameter types
  80  * are systematically presented in two versions, so that both Java arrays and
  81  * Java lists can be used to work with groups of parameter types.
  82  * The query methods {@code parameterArray} and {@code parameterList}
  83  * also provide a choice between arrays and lists.
  84  * <p>
  85  * {@code MethodType} objects are sometimes derived from bytecode instructions
  86  * such as {@code invokedynamic}, specifically from the type descriptor strings associated
  87  * with the instructions in a class file's constant pool.
  88  * <p>
  89  * Like classes and strings, method types can also be represented directly
  90  * in a class file's constant pool as constants.
  91  * A method type may be loaded by an {@code ldc} instruction which refers
  92  * to a suitable {@code CONSTANT_MethodType} constant pool entry.
  93  * The entry refers to a {@code CONSTANT_Utf8} spelling for the descriptor string.
  94  * (For full details on method type constants, see sections {@jvms
  95  * 4.4.8} and {@jvms 5.4.3.5} of the Java Virtual Machine
  96  * Specification.)
  97  * <p>
  98  * When the JVM materializes a {@code MethodType} from a descriptor string,
  99  * all classes named in the descriptor must be accessible, and will be loaded.
 100  * (But the classes need not be initialized, as is the case with a {@code CONSTANT_Class}.)
 101  * This loading may occur at any time before the {@code MethodType} object is first derived.
 102  * <p>
 103  * <b><a id="descriptor">Nominal Descriptors</a></b>
 104  * <p>
 105  * A {@code MethodType} can be described in {@linkplain MethodTypeDesc nominal form}
 106  * if and only if all of the parameter types and return type can be described
 107  * with a {@link Class#describeConstable() nominal descriptor} represented by
 108  * {@link ClassDesc}.  If a method type can be described norminally, then:
 109  * <ul>
 110  * <li>The method type has a {@link MethodTypeDesc nominal descriptor}
 111  *     returned by {@link #describeConstable() MethodType::describeConstable}.</li>
 112  * <li>The descriptor string returned by
 113  *     {@link #descriptorString() MethodType::descriptorString} or
 114  *     {@link #toMethodDescriptorString() MethodType::toMethodDescriptorString}
 115  *     for the method type is a method descriptor (JVMS {@jvms 4.3.3}).</li>
 116  * </ul>
 117  * <p>
 118  * If any of the parameter types or return type cannot be described
 119  * nominally, i.e. {@link Class#describeConstable() Class::describeConstable}
 120  * returns an empty optional for that type,
 121  * then the method type cannot be described nominally:
 122  * <ul>
 123  * <li>The method type has no {@link MethodTypeDesc nominal descriptor} and
 124  *     {@link #describeConstable() MethodType::describeConstable} returns
 125  *     an empty optional.</li>
 126  * <li>The descriptor string returned by
 127  *     {@link #descriptorString() MethodType::descriptorString} or
 128  *     {@link #toMethodDescriptorString() MethodType::toMethodDescriptorString}
 129  *     for the method type is not a type descriptor.</li>
 130  * </ul>
 131  *
 132  * @author John Rose, JSR 292 EG
 133  * @since 1.7
 134  */
 135 public final
 136 class MethodType
 137         implements Constable,
 138                    TypeDescriptor.OfMethod<Class<?>, MethodType>,
 139                    java.io.Serializable {
 140     @java.io.Serial
 141     private static final long serialVersionUID = 292L;  // {rtype, {ptype...}}
 142 
 143     // The rtype and ptypes fields define the structural identity of the method type:
 144     private final @Stable Class<?>   rtype;
 145     private final @Stable Class<?>[] ptypes;
 146 
 147     // The remaining fields are caches of various sorts:
 148     private @Stable MethodTypeForm form; // erased form, plus cached data about primitives
 149     private @Stable MethodType wrapAlt;  // alternative wrapped/unwrapped version
 150     private @Stable Invokers invokers;   // cache of handy higher-order adapters
 151     private @Stable String methodDescriptor;  // cache for toMethodDescriptorString
 152 
 153     /**
 154      * Constructor that performs no copying or validation.
 155      * Should only be called from the factory method makeImpl
 156      */
 157     private MethodType(Class<?> rtype, Class<?>[] ptypes) {
 158         this.rtype = rtype;
 159         this.ptypes = ptypes;
 160     }
 161 
 162     /*trusted*/ MethodTypeForm form() { return form; }
 163     /*trusted*/ Class<?> rtype() { return rtype; }
 164     /*trusted*/ Class<?>[] ptypes() { return ptypes; }
 165 
 166     void setForm(MethodTypeForm f) { form = f; }
 167 
 168     /** This number, mandated by the JVM spec as 255,
 169      *  is the maximum number of <em>slots</em>
 170      *  that any Java method can receive in its argument list.
 171      *  It limits both JVM signatures and method type objects.
 172      *  The longest possible invocation will look like
 173      *  {@code staticMethod(arg1, arg2, ..., arg255)} or
 174      *  {@code x.virtualMethod(arg1, arg2, ..., arg254)}.
 175      */
 176     /*non-public*/
 177     static final int MAX_JVM_ARITY = 255;  // this is mandated by the JVM spec.
 178 
 179     /** This number is the maximum arity of a method handle, 254.
 180      *  It is derived from the absolute JVM-imposed arity by subtracting one,
 181      *  which is the slot occupied by the method handle itself at the
 182      *  beginning of the argument list used to invoke the method handle.
 183      *  The longest possible invocation will look like
 184      *  {@code mh.invoke(arg1, arg2, ..., arg254)}.
 185      */
 186     // Issue:  Should we allow MH.invokeWithArguments to go to the full 255?
 187     /*non-public*/
 188     static final int MAX_MH_ARITY = MAX_JVM_ARITY-1;  // deduct one for mh receiver
 189 
 190     /** This number is the maximum arity of a method handle invoker, 253.
 191      *  It is derived from the absolute JVM-imposed arity by subtracting two,
 192      *  which are the slots occupied by invoke method handle, and the
 193      *  target method handle, which are both at the beginning of the argument
 194      *  list used to invoke the target method handle.
 195      *  The longest possible invocation will look like
 196      *  {@code invokermh.invoke(targetmh, arg1, arg2, ..., arg253)}.
 197      */
 198     /*non-public*/
 199     static final int MAX_MH_INVOKER_ARITY = MAX_MH_ARITY-1;  // deduct one more for invoker
 200 
 201     private static void checkRtype(Class<?> rtype) {
 202         Objects.requireNonNull(rtype);
 203     }
 204     private static void checkPtype(Class<?> ptype) {
 205         Objects.requireNonNull(ptype);
 206         if (ptype == void.class)
 207             throw newIllegalArgumentException("parameter type cannot be void");
 208     }
 209     /** Return number of extra slots (count of long/double args). */
 210     private static int checkPtypes(Class<?>[] ptypes) {
 211         int slots = 0;
 212         for (Class<?> ptype : ptypes) {
 213             checkPtype(ptype);
 214             if (ptype == double.class || ptype == long.class) {
 215                 slots++;
 216             }
 217         }
 218         checkSlotCount(ptypes.length + slots);
 219         return slots;
 220     }
 221 
 222     static {
 223         // MAX_JVM_ARITY must be power of 2 minus 1 for following code trick to work:
 224         assert((MAX_JVM_ARITY & (MAX_JVM_ARITY+1)) == 0);
 225     }
 226     static void checkSlotCount(int count) {
 227         if ((count & MAX_JVM_ARITY) != count)
 228             throw newIllegalArgumentException("bad parameter count "+count);
 229     }
 230     private static IndexOutOfBoundsException newIndexOutOfBoundsException(Object num) {
 231         if (num instanceof Integer)  num = "bad index: "+num;
 232         return new IndexOutOfBoundsException(num.toString());
 233     }
 234 
 235     static final ConcurrentWeakInternSet<MethodType> internTable = new ConcurrentWeakInternSet<>();
 236 
 237     static final Class<?>[] NO_PTYPES = {};
 238 
 239     /**
 240      * Finds or creates an instance of the given method type.
 241      * @param rtype  the return type
 242      * @param ptypes the parameter types
 243      * @return a method type with the given components
 244      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 245      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 246      */
 247     public static MethodType methodType(Class<?> rtype, Class<?>[] ptypes) {
 248         return makeImpl(rtype, ptypes, false);
 249     }
 250 
 251     /**
 252      * Finds or creates a method type with the given components.
 253      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 254      * @param rtype  the return type
 255      * @param ptypes the parameter types
 256      * @return a method type with the given components
 257      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 258      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 259      */
 260     public static MethodType methodType(Class<?> rtype, List<Class<?>> ptypes) {
 261         boolean notrust = false;  // random List impl. could return evil ptypes array
 262         return makeImpl(rtype, listToArray(ptypes), notrust);
 263     }
 264 
 265     private static Class<?>[] listToArray(List<Class<?>> ptypes) {
 266         // sanity check the size before the toArray call, since size might be huge
 267         checkSlotCount(ptypes.size());
 268         return ptypes.toArray(NO_PTYPES);
 269     }
 270 
 271     /**
 272      * Finds or creates a method type with the given components.
 273      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 274      * The leading parameter type is prepended to the remaining array.
 275      * @param rtype  the return type
 276      * @param ptype0 the first parameter type
 277      * @param ptypes the remaining parameter types
 278      * @return a method type with the given components
 279      * @throws NullPointerException if {@code rtype} or {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is null
 280      * @throws IllegalArgumentException if {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is {@code void.class}
 281      */
 282     public static MethodType methodType(Class<?> rtype, Class<?> ptype0, Class<?>... ptypes) {
 283         Class<?>[] ptypes1 = new Class<?>[1+ptypes.length];
 284         ptypes1[0] = ptype0;
 285         System.arraycopy(ptypes, 0, ptypes1, 1, ptypes.length);
 286         return makeImpl(rtype, ptypes1, true);
 287     }
 288 
 289     /**
 290      * Finds or creates a method type with the given components.
 291      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 292      * The resulting method has no parameter types.
 293      * @param rtype  the return type
 294      * @return a method type with the given return value
 295      * @throws NullPointerException if {@code rtype} is null
 296      */
 297     public static MethodType methodType(Class<?> rtype) {
 298         return makeImpl(rtype, NO_PTYPES, true);
 299     }
 300 
 301     /**
 302      * Finds or creates a method type with the given components.
 303      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 304      * The resulting method has the single given parameter type.
 305      * @param rtype  the return type
 306      * @param ptype0 the parameter type
 307      * @return a method type with the given return value and parameter type
 308      * @throws NullPointerException if {@code rtype} or {@code ptype0} is null
 309      * @throws IllegalArgumentException if {@code ptype0} is {@code void.class}
 310      */
 311     public static MethodType methodType(Class<?> rtype, Class<?> ptype0) {
 312         return makeImpl(rtype, new Class<?>[]{ ptype0 }, true);
 313     }
 314 
 315     /**
 316      * Finds or creates a method type with the given components.
 317      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 318      * The resulting method has the same parameter types as {@code ptypes},
 319      * and the specified return type.
 320      * @param rtype  the return type
 321      * @param ptypes the method type which supplies the parameter types
 322      * @return a method type with the given components
 323      * @throws NullPointerException if {@code rtype} or {@code ptypes} is null
 324      */
 325     public static MethodType methodType(Class<?> rtype, MethodType ptypes) {
 326         return makeImpl(rtype, ptypes.ptypes, true);
 327     }
 328 
 329     /**
 330      * Sole factory method to find or create an interned method type.
 331      * @param rtype desired return type
 332      * @param ptypes desired parameter types
 333      * @param trusted whether the ptypes can be used without cloning
 334      * @return the unique method type of the desired structure
 335      */
 336     /*trusted*/
 337     static MethodType makeImpl(Class<?> rtype, Class<?>[] ptypes, boolean trusted) {
 338         if (ptypes.length == 0) {
 339             ptypes = NO_PTYPES; trusted = true;
 340         }
 341         MethodType primordialMT = new MethodType(rtype, ptypes);
 342         MethodType mt = internTable.get(primordialMT);
 343         if (mt != null)
 344             return mt;
 345 
 346         // promote the object to the Real Thing, and reprobe
 347         MethodType.checkRtype(rtype);
 348         if (trusted) {
 349             MethodType.checkPtypes(ptypes);
 350             mt = primordialMT;
 351         } else {
 352             // Make defensive copy then validate
 353             ptypes = Arrays.copyOf(ptypes, ptypes.length);
 354             MethodType.checkPtypes(ptypes);
 355             mt = new MethodType(rtype, ptypes);
 356         }
 357         mt.form = MethodTypeForm.findForm(mt);
 358         return internTable.add(mt);
 359     }
 360     private static final @Stable MethodType[] objectOnlyTypes = new MethodType[20];
 361 
 362     /**
 363      * Finds or creates a method type whose components are {@code Object} with an optional trailing {@code Object[]} array.
 364      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 365      * All parameters and the return type will be {@code Object},
 366      * except the final array parameter if any, which will be {@code Object[]}.
 367      * @param objectArgCount number of parameters (excluding the final array parameter if any)
 368      * @param finalArray whether there will be a trailing array parameter, of type {@code Object[]}
 369      * @return a generally applicable method type, for all calls of the given fixed argument count and a collected array of further arguments
 370      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255 (or 254, if {@code finalArray} is true)
 371      * @see #genericMethodType(int)
 372      */
 373     public static MethodType genericMethodType(int objectArgCount, boolean finalArray) {
 374         MethodType mt;
 375         checkSlotCount(objectArgCount);
 376         int ivarargs = (!finalArray ? 0 : 1);
 377         int ootIndex = objectArgCount*2 + ivarargs;
 378         if (ootIndex < objectOnlyTypes.length) {
 379             mt = objectOnlyTypes[ootIndex];
 380             if (mt != null)  return mt;
 381         }
 382         Class<?>[] ptypes = new Class<?>[objectArgCount + ivarargs];
 383         Arrays.fill(ptypes, Object.class);
 384         if (ivarargs != 0)  ptypes[objectArgCount] = Object[].class;
 385         mt = makeImpl(Object.class, ptypes, true);
 386         if (ootIndex < objectOnlyTypes.length) {
 387             objectOnlyTypes[ootIndex] = mt;     // cache it here also!
 388         }
 389         return mt;
 390     }
 391 
 392     /**
 393      * Finds or creates a method type whose components are all {@code Object}.
 394      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 395      * All parameters and the return type will be Object.
 396      * @param objectArgCount number of parameters
 397      * @return a generally applicable method type, for all calls of the given argument count
 398      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255
 399      * @see #genericMethodType(int, boolean)
 400      */
 401     public static MethodType genericMethodType(int objectArgCount) {
 402         return genericMethodType(objectArgCount, false);
 403     }
 404 
 405     /**
 406      * Finds or creates a method type with a single different parameter type.
 407      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 408      * @param num    the index (zero-based) of the parameter type to change
 409      * @param nptype a new parameter type to replace the old one with
 410      * @return the same type, except with the selected parameter changed
 411      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}
 412      * @throws IllegalArgumentException if {@code nptype} is {@code void.class}
 413      * @throws NullPointerException if {@code nptype} is null
 414      */
 415     public MethodType changeParameterType(int num, Class<?> nptype) {
 416         if (parameterType(num) == nptype)  return this;
 417         checkPtype(nptype);
 418         Class<?>[] nptypes = ptypes.clone();
 419         nptypes[num] = nptype;
 420         return makeImpl(rtype, nptypes, true);
 421     }
 422 
 423     /**
 424      * Finds or creates a method type with additional parameter types.
 425      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 426      * @param num    the position (zero-based) of the inserted parameter type(s)
 427      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 428      * @return the same type, except with the selected parameter(s) inserted
 429      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}
 430      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 431      *                                  or if the resulting method type would have more than 255 parameter slots
 432      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 433      */
 434     public MethodType insertParameterTypes(int num, Class<?>... ptypesToInsert) {
 435         int len = ptypes.length;
 436         if (num < 0 || num > len)
 437             throw newIndexOutOfBoundsException(num);
 438         int ins = checkPtypes(ptypesToInsert);
 439         checkSlotCount(parameterSlotCount() + ptypesToInsert.length + ins);
 440         int ilen = ptypesToInsert.length;
 441         if (ilen == 0)  return this;
 442         Class<?>[] nptypes = new Class<?>[len + ilen];
 443         if (num > 0) {
 444             System.arraycopy(ptypes, 0, nptypes, 0, num);
 445         }
 446         System.arraycopy(ptypesToInsert, 0, nptypes, num, ilen);
 447         if (num < len) {
 448             System.arraycopy(ptypes, num, nptypes, num+ilen, len-num);
 449         }
 450         return makeImpl(rtype, nptypes, true);
 451     }
 452 
 453     /**
 454      * Finds or creates a method type with additional parameter types.
 455      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 456      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list
 457      * @return the same type, except with the selected parameter(s) appended
 458      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 459      *                                  or if the resulting method type would have more than 255 parameter slots
 460      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 461      */
 462     public MethodType appendParameterTypes(Class<?>... ptypesToInsert) {
 463         return insertParameterTypes(parameterCount(), ptypesToInsert);
 464     }
 465 
 466     /**
 467      * Finds or creates a method type with additional parameter types.
 468      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 469      * @param num    the position (zero-based) of the inserted parameter type(s)
 470      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 471      * @return the same type, except with the selected parameter(s) inserted
 472      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}
 473      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 474      *                                  or if the resulting method type would have more than 255 parameter slots
 475      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 476      */
 477     public MethodType insertParameterTypes(int num, List<Class<?>> ptypesToInsert) {
 478         return insertParameterTypes(num, listToArray(ptypesToInsert));
 479     }
 480 
 481     /**
 482      * Finds or creates a method type with additional parameter types.
 483      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 484      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list
 485      * @return the same type, except with the selected parameter(s) appended
 486      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 487      *                                  or if the resulting method type would have more than 255 parameter slots
 488      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 489      */
 490     public MethodType appendParameterTypes(List<Class<?>> ptypesToInsert) {
 491         return insertParameterTypes(parameterCount(), ptypesToInsert);
 492     }
 493 
 494     /**
 495      * Finds or creates a method type with modified parameter types.
 496      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 497      * @param start  the position (zero-based) of the first replaced parameter type(s)
 498      * @param end    the position (zero-based) after the last replaced parameter type(s)
 499      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 500      * @return the same type, except with the selected parameter(s) replaced
 501      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}
 502      *                                  or if {@code end} is negative or greater than {@code parameterCount()}
 503      *                                  or if {@code start} is greater than {@code end}
 504      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 505      *                                  or if the resulting method type would have more than 255 parameter slots
 506      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 507      */
 508     /*non-public*/
 509     MethodType replaceParameterTypes(int start, int end, Class<?>... ptypesToInsert) {
 510         if (start == end)
 511             return insertParameterTypes(start, ptypesToInsert);
 512         int len = ptypes.length;
 513         if (!(0 <= start && start <= end && end <= len))
 514             throw newIndexOutOfBoundsException("start="+start+" end="+end);
 515         int ilen = ptypesToInsert.length;
 516         if (ilen == 0)
 517             return dropParameterTypes(start, end);
 518         return dropParameterTypes(start, end).insertParameterTypes(start, ptypesToInsert);
 519     }
 520 
 521     /** Replace the last arrayLength parameter types with the component type of arrayType.
 522      * @param arrayType any array type
 523      * @param pos position at which to spread
 524      * @param arrayLength the number of parameter types to change
 525      * @return the resulting type
 526      */
 527     /*non-public*/
 528     MethodType asSpreaderType(Class<?> arrayType, int pos, int arrayLength) {
 529         assert(parameterCount() >= arrayLength);
 530         int spreadPos = pos;
 531         if (arrayLength == 0)  return this;  // nothing to change
 532         if (arrayType == Object[].class) {
 533             if (isGeneric())  return this;  // nothing to change
 534             if (spreadPos == 0) {
 535                 // no leading arguments to preserve; go generic
 536                 MethodType res = genericMethodType(arrayLength);
 537                 if (rtype != Object.class) {
 538                     res = res.changeReturnType(rtype);
 539                 }
 540                 return res;
 541             }
 542         }
 543         Class<?> elemType = arrayType.getComponentType();
 544         assert(elemType != null);
 545         for (int i = spreadPos; i < spreadPos + arrayLength; i++) {
 546             if (ptypes[i] != elemType) {
 547                 Class<?>[] fixedPtypes = ptypes.clone();
 548                 Arrays.fill(fixedPtypes, i, spreadPos + arrayLength, elemType);
 549                 return methodType(rtype, fixedPtypes);
 550             }
 551         }
 552         return this;  // arguments check out; no change
 553     }
 554 
 555     /** Return the leading parameter type, which must exist and be a reference.
 556      *  @return the leading parameter type, after error checks
 557      */
 558     /*non-public*/
 559     Class<?> leadingReferenceParameter() {
 560         Class<?> ptype;
 561         if (ptypes.length == 0 ||
 562             (ptype = ptypes[0]).isPrimitive())
 563             throw newIllegalArgumentException("no leading reference parameter");
 564         return ptype;
 565     }
 566 
 567     /** Delete the last parameter type and replace it with arrayLength copies of the component type of arrayType.
 568      * @param arrayType any array type
 569      * @param pos position at which to insert parameters
 570      * @param arrayLength the number of parameter types to insert
 571      * @return the resulting type
 572      */
 573     /*non-public*/
 574     MethodType asCollectorType(Class<?> arrayType, int pos, int arrayLength) {
 575         assert(parameterCount() >= 1);
 576         assert(pos < ptypes.length);
 577         assert(ptypes[pos].isAssignableFrom(arrayType));
 578         MethodType res;
 579         if (arrayType == Object[].class) {
 580             res = genericMethodType(arrayLength);
 581             if (rtype != Object.class) {
 582                 res = res.changeReturnType(rtype);
 583             }
 584         } else {
 585             Class<?> elemType = arrayType.getComponentType();
 586             assert(elemType != null);
 587             res = methodType(rtype, Collections.nCopies(arrayLength, elemType));
 588         }
 589         if (ptypes.length == 1) {
 590             return res;
 591         } else {
 592             // insert after (if need be), then before
 593             if (pos < ptypes.length - 1) {
 594                 res = res.insertParameterTypes(arrayLength, Arrays.copyOfRange(ptypes, pos + 1, ptypes.length));
 595             }
 596             return res.insertParameterTypes(0, Arrays.copyOf(ptypes, pos));
 597         }
 598     }
 599 
 600     /**
 601      * Finds or creates a method type with some parameter types omitted.
 602      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 603      * @param start  the index (zero-based) of the first parameter type to remove
 604      * @param end    the index (greater than {@code start}) of the first parameter type after not to remove
 605      * @return the same type, except with the selected parameter(s) removed
 606      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}
 607      *                                  or if {@code end} is negative or greater than {@code parameterCount()}
 608      *                                  or if {@code start} is greater than {@code end}
 609      */
 610     public MethodType dropParameterTypes(int start, int end) {
 611         int len = ptypes.length;
 612         if (!(0 <= start && start <= end && end <= len))
 613             throw newIndexOutOfBoundsException("start="+start+" end="+end);
 614         if (start == end)  return this;
 615         Class<?>[] nptypes;
 616         if (start == 0) {
 617             if (end == len) {
 618                 // drop all parameters
 619                 nptypes = NO_PTYPES;
 620             } else {
 621                 // drop initial parameter(s)
 622                 nptypes = Arrays.copyOfRange(ptypes, end, len);
 623             }
 624         } else {
 625             if (end == len) {
 626                 // drop trailing parameter(s)
 627                 nptypes = Arrays.copyOfRange(ptypes, 0, start);
 628             } else {
 629                 int tail = len - end;
 630                 nptypes = Arrays.copyOfRange(ptypes, 0, start + tail);
 631                 System.arraycopy(ptypes, end, nptypes, start, tail);
 632             }
 633         }
 634         return makeImpl(rtype, nptypes, true);
 635     }
 636 
 637     /**
 638      * Finds or creates a method type with a different return type.
 639      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 640      * @param nrtype a return parameter type to replace the old one with
 641      * @return the same type, except with the return type change
 642      * @throws NullPointerException if {@code nrtype} is null
 643      */
 644     public MethodType changeReturnType(Class<?> nrtype) {
 645         if (returnType() == nrtype)  return this;
 646         return makeImpl(nrtype, ptypes, true);
 647     }
 648 
 649     /**
 650      * Reports if this type contains a primitive argument or return value.
 651      * The return type {@code void} counts as a primitive.
 652      * @return true if any of the types are primitives
 653      */
 654     public boolean hasPrimitives() {
 655         return form.hasPrimitives();
 656     }
 657 
 658     /**
 659      * Reports if this type contains a wrapper argument or return value.
 660      * Wrappers are types which box primitive values, such as {@link Integer}.
 661      * The reference type {@code java.lang.Void} counts as a wrapper,
 662      * if it occurs as a return type.
 663      * @return true if any of the types are wrappers
 664      */
 665     public boolean hasWrappers() {
 666         return unwrap() != this;
 667     }
 668 
 669     /**
 670      * Erases all reference types to {@code Object}.
 671      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 672      * All primitive types (including {@code void}) will remain unchanged.
 673      * @return a version of the original type with all reference types replaced
 674      */
 675     public MethodType erase() {
 676         return form.erasedType();
 677     }
 678 
 679     /**
 680      * Erases all reference types to {@code Object}, and all subword types to {@code int}.
 681      * This is the reduced type polymorphism used by private methods
 682      * such as {@link MethodHandle#invokeBasic invokeBasic}.
 683      * @return a version of the original type with all reference and subword types replaced
 684      */
 685     /*non-public*/
 686     MethodType basicType() {
 687         return form.basicType();
 688     }
 689 
 690     private static final @Stable Class<?>[] METHOD_HANDLE_ARRAY
 691             = new Class<?>[] { MethodHandle.class };
 692 
 693     /**
 694      * @return a version of the original type with MethodHandle prepended as the first argument
 695      */
 696     /*non-public*/
 697     MethodType invokerType() {
 698         return insertParameterTypes(0, METHOD_HANDLE_ARRAY);
 699     }
 700 
 701     /**
 702      * Converts all types, both reference and primitive, to {@code Object}.
 703      * Convenience method for {@link #genericMethodType(int) genericMethodType}.
 704      * The expression {@code type.wrap().erase()} produces the same value
 705      * as {@code type.generic()}.
 706      * @return a version of the original type with all types replaced
 707      */
 708     public MethodType generic() {
 709         return genericMethodType(parameterCount());
 710     }
 711 
 712     /*non-public*/
 713     boolean isGeneric() {
 714         return this == erase() && !hasPrimitives();
 715     }
 716 
 717     /**
 718      * Converts all primitive types to their corresponding wrapper types.
 719      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 720      * All reference types (including wrapper types) will remain unchanged.
 721      * A {@code void} return type is changed to the type {@code java.lang.Void}.
 722      * The expression {@code type.wrap().erase()} produces the same value
 723      * as {@code type.generic()}.
 724      * @return a version of the original type with all primitive types replaced
 725      */
 726     public MethodType wrap() {
 727         return hasPrimitives() ? wrapWithPrims(this) : this;
 728     }
 729 
 730     /**
 731      * Converts all wrapper types to their corresponding primitive types.
 732      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 733      * All primitive types (including {@code void}) will remain unchanged.
 734      * A return type of {@code java.lang.Void} is changed to {@code void}.
 735      * @return a version of the original type with all wrapper types replaced
 736      */
 737     public MethodType unwrap() {
 738         MethodType noprims = !hasPrimitives() ? this : wrapWithPrims(this);
 739         return unwrapWithNoPrims(noprims);
 740     }
 741 
 742     private static MethodType wrapWithPrims(MethodType pt) {
 743         assert(pt.hasPrimitives());
 744         MethodType wt = pt.wrapAlt;
 745         if (wt == null) {
 746             // fill in lazily
 747             wt = MethodTypeForm.canonicalize(pt, MethodTypeForm.WRAP, MethodTypeForm.WRAP);
 748             assert(wt != null);
 749             pt.wrapAlt = wt;
 750         }
 751         return wt;
 752     }
 753 
 754     private static MethodType unwrapWithNoPrims(MethodType wt) {
 755         assert(!wt.hasPrimitives());
 756         MethodType uwt = wt.wrapAlt;
 757         if (uwt == null) {
 758             // fill in lazily
 759             uwt = MethodTypeForm.canonicalize(wt, MethodTypeForm.UNWRAP, MethodTypeForm.UNWRAP);
 760             if (uwt == null)
 761                 uwt = wt;    // type has no wrappers or prims at all
 762             wt.wrapAlt = uwt;
 763         }
 764         return uwt;
 765     }
 766 
 767     /**
 768      * Returns the parameter type at the specified index, within this method type.
 769      * @param num the index (zero-based) of the desired parameter type
 770      * @return the selected parameter type
 771      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}
 772      */
 773     public Class<?> parameterType(int num) {
 774         return ptypes[num];
 775     }
 776     /**
 777      * Returns the number of parameter types in this method type.
 778      * @return the number of parameter types
 779      */
 780     public int parameterCount() {
 781         return ptypes.length;
 782     }
 783     /**
 784      * Returns the return type of this method type.
 785      * @return the return type
 786      */
 787     public Class<?> returnType() {
 788         return rtype;
 789     }
 790 
 791     /**
 792      * Presents the parameter types as a list (a convenience method).
 793      * The list will be immutable.
 794      * @return the parameter types (as an immutable list)
 795      */
 796     public List<Class<?>> parameterList() {
 797         return Collections.unmodifiableList(Arrays.asList(ptypes.clone()));
 798     }
 799 
 800     /**
 801      * Returns the last parameter type of this method type.
 802      * If this type has no parameters, the sentinel value
 803      * {@code void.class} is returned instead.
 804      * @apiNote
 805      * <p>
 806      * The sentinel value is chosen so that reflective queries can be
 807      * made directly against the result value.
 808      * The sentinel value cannot be confused with a real parameter,
 809      * since {@code void} is never acceptable as a parameter type.
 810      * For variable arity invocation modes, the expression
 811      * {@link Class#getComponentType lastParameterType().getComponentType()}
 812      * is useful to query the type of the "varargs" parameter.
 813      * @return the last parameter type if any, else {@code void.class}
 814      * @since 10
 815      */
 816     public Class<?> lastParameterType() {
 817         int len = ptypes.length;
 818         return len == 0 ? void.class : ptypes[len-1];
 819     }
 820 
 821     /**
 822      * Presents the parameter types as an array (a convenience method).
 823      * Changes to the array will not result in changes to the type.
 824      * @return the parameter types (as a fresh copy if necessary)
 825      */
 826     public Class<?>[] parameterArray() {
 827         return ptypes.clone();
 828     }
 829 
 830     /**
 831      * Compares the specified object with this type for equality.
 832      * That is, it returns {@code true} if and only if the specified object
 833      * is also a method type with exactly the same parameters and return type.
 834      * @param x object to compare
 835      * @see Object#equals(Object)
 836      */
 837     // This implementation may also return true if x is a WeakEntry containing
 838     // a method type that is equal to this. This is an internal implementation
 839     // detail to allow for faster method type lookups.
 840     // See ConcurrentWeakInternSet.WeakEntry#equals(Object)
 841     @Override
 842     public boolean equals(Object x) {
 843         if (this == x) {
 844             return true;
 845         }
 846         if (x instanceof MethodType) {
 847             return equals((MethodType)x);
 848         }
 849         if (x instanceof ConcurrentWeakInternSet.WeakEntry) {
 850             Object o = ((ConcurrentWeakInternSet.WeakEntry)x).get();
 851             if (o instanceof MethodType) {
 852                 return equals((MethodType)o);
 853             }
 854         }
 855         return false;
 856     }
 857 
 858     private boolean equals(MethodType that) {
 859         return this.rtype == that.rtype
 860             && Arrays.equals(this.ptypes, that.ptypes);
 861     }
 862 
 863     /**
 864      * Returns the hash code value for this method type.
 865      * It is defined to be the same as the hashcode of a List
 866      * whose elements are the return type followed by the
 867      * parameter types.
 868      * @return the hash code value for this method type
 869      * @see Object#hashCode()
 870      * @see #equals(Object)
 871      * @see List#hashCode()
 872      */
 873     @Override
 874     public int hashCode() {
 875         int hashCode = 31 + rtype.hashCode();
 876         for (Class<?> ptype : ptypes)
 877             hashCode = 31 * hashCode + ptype.hashCode();
 878         return hashCode;
 879     }
 880 
 881     /**
 882      * Returns a string representation of the method type,
 883      * of the form {@code "(PT0,PT1...)RT"}.
 884      * The string representation of a method type is a
 885      * parenthesis enclosed, comma separated list of type names,
 886      * followed immediately by the return type.
 887      * <p>
 888      * Each type is represented by its
 889      * {@link java.lang.Class#getSimpleName simple name}.
 890      */
 891     @Override
 892     public String toString() {
 893         StringJoiner sj = new StringJoiner(",", "(",
 894                 ")" + rtype.getSimpleName());
 895         for (int i = 0; i < ptypes.length; i++) {
 896             sj.add(ptypes[i].getSimpleName());
 897         }
 898         return sj.toString();
 899     }
 900 
 901     /** True if my parameter list is effectively identical to the given full list,
 902      *  after skipping the given number of my own initial parameters.
 903      *  In other words, after disregarding {@code skipPos} parameters,
 904      *  my remaining parameter list is no longer than the {@code fullList}, and
 905      *  is equal to the same-length initial sublist of {@code fullList}.
 906      */
 907     /*non-public*/
 908     boolean effectivelyIdenticalParameters(int skipPos, List<Class<?>> fullList) {
 909         int myLen = ptypes.length, fullLen = fullList.size();
 910         if (skipPos > myLen || myLen - skipPos > fullLen)
 911             return false;
 912         List<Class<?>> myList = Arrays.asList(ptypes);
 913         if (skipPos != 0) {
 914             myList = myList.subList(skipPos, myLen);
 915             myLen -= skipPos;
 916         }
 917         if (fullLen == myLen)
 918             return myList.equals(fullList);
 919         else
 920             return myList.equals(fullList.subList(0, myLen));
 921     }
 922 
 923     /** True if the old return type can always be viewed (w/o casting) under new return type,
 924      *  and the new parameters can be viewed (w/o casting) under the old parameter types.
 925      */
 926     /*non-public*/
 927     boolean isViewableAs(MethodType newType, boolean keepInterfaces) {
 928         if (!VerifyType.isNullConversion(returnType(), newType.returnType(), keepInterfaces))
 929             return false;
 930         if (form == newType.form && form.erasedType == this)
 931             return true;  // my reference parameters are all Object
 932         if (ptypes == newType.ptypes)
 933             return true;
 934         int argc = parameterCount();
 935         if (argc != newType.parameterCount())
 936             return false;
 937         for (int i = 0; i < argc; i++) {
 938             if (!VerifyType.isNullConversion(newType.parameterType(i), parameterType(i), keepInterfaces))
 939                 return false;
 940         }
 941         return true;
 942     }
 943     /*non-public*/
 944     boolean isConvertibleTo(MethodType newType) {
 945         MethodTypeForm oldForm = this.form();
 946         MethodTypeForm newForm = newType.form();
 947         if (oldForm == newForm)
 948             // same parameter count, same primitive/object mix
 949             return true;
 950         if (!canConvert(returnType(), newType.returnType()))
 951             return false;
 952         Class<?>[] srcTypes = newType.ptypes;
 953         Class<?>[] dstTypes = ptypes;
 954         if (srcTypes == dstTypes)
 955             return true;
 956         int argc;
 957         if ((argc = srcTypes.length) != dstTypes.length)
 958             return false;
 959         if (argc <= 1) {
 960             if (argc == 1 && !canConvert(srcTypes[0], dstTypes[0]))
 961                 return false;
 962             return true;
 963         }
 964         if ((!oldForm.hasPrimitives() && oldForm.erasedType == this) ||
 965             (!newForm.hasPrimitives() && newForm.erasedType == newType)) {
 966             // Somewhat complicated test to avoid a loop of 2 or more trips.
 967             // If either type has only Object parameters, we know we can convert.
 968             assert(canConvertParameters(srcTypes, dstTypes));
 969             return true;
 970         }
 971         return canConvertParameters(srcTypes, dstTypes);
 972     }
 973 
 974     /** Returns true if MHs.explicitCastArguments produces the same result as MH.asType.
 975      *  If the type conversion is impossible for either, the result should be false.
 976      */
 977     /*non-public*/
 978     boolean explicitCastEquivalentToAsType(MethodType newType) {
 979         if (this == newType)  return true;
 980         if (!explicitCastEquivalentToAsType(rtype, newType.rtype)) {
 981             return false;
 982         }
 983         Class<?>[] srcTypes = newType.ptypes;
 984         Class<?>[] dstTypes = ptypes;
 985         if (dstTypes == srcTypes) {
 986             return true;
 987         }
 988         assert(dstTypes.length == srcTypes.length);
 989         for (int i = 0; i < dstTypes.length; i++) {
 990             if (!explicitCastEquivalentToAsType(srcTypes[i], dstTypes[i])) {
 991                 return false;
 992             }
 993         }
 994         return true;
 995     }
 996 
 997     /** Reports true if the src can be converted to the dst, by both asType and MHs.eCE,
 998      *  and with the same effect.
 999      *  MHs.eCA has the following "upgrades" to MH.asType:
1000      *  1. interfaces are unchecked (that is, treated as if aliased to Object)
1001      *     Therefore, {@code Object->CharSequence} is possible in both cases but has different semantics
1002      *  2. the full matrix of primitive-to-primitive conversions is supported
1003      *     Narrowing like {@code long->byte} and basic-typing like {@code boolean->int}
1004      *     are not supported by asType, but anything supported by asType is equivalent
1005      *     with MHs.eCE.
1006      *  3a. unboxing conversions can be followed by the full matrix of primitive conversions
1007      *  3b. unboxing of null is permitted (creates a zero primitive value)
1008      * Other than interfaces, reference-to-reference conversions are the same.
1009      * Boxing primitives to references is the same for both operators.
1010      */
1011     private static boolean explicitCastEquivalentToAsType(Class<?> src, Class<?> dst) {
1012         if (src == dst || dst == Object.class || dst == void.class)  return true;
1013         if (src.isPrimitive()) {
1014             // Could be a prim/prim conversion, where casting is a strict superset.
1015             // Or a boxing conversion, which is always to an exact wrapper class.
1016             return canConvert(src, dst);
1017         } else if (dst.isPrimitive()) {
1018             // Unboxing behavior is different between MHs.eCA & MH.asType (see 3b).
1019             return false;
1020         } else {
1021             // R->R always works, but we have to avoid a check-cast to an interface.
1022             return !dst.isInterface() || dst.isAssignableFrom(src);
1023         }
1024     }
1025 
1026     private boolean canConvertParameters(Class<?>[] srcTypes, Class<?>[] dstTypes) {
1027         for (int i = 0; i < srcTypes.length; i++) {
1028             if (!canConvert(srcTypes[i], dstTypes[i])) {
1029                 return false;
1030             }
1031         }
1032         return true;
1033     }
1034 
1035     /*non-public*/
1036     static boolean canConvert(Class<?> src, Class<?> dst) {
1037         // short-circuit a few cases:
1038         if (src == dst || src == Object.class || dst == Object.class)  return true;
1039         // the remainder of this logic is documented in MethodHandle.asType
1040         if (src.isPrimitive()) {
1041             // can force void to an explicit null, a la reflect.Method.invoke
1042             // can also force void to a primitive zero, by analogy
1043             if (src == void.class)  return true;  //or !dst.isPrimitive()?
1044             Wrapper sw = Wrapper.forPrimitiveType(src);
1045             if (dst.isPrimitive()) {
1046                 // P->P must widen
1047                 return Wrapper.forPrimitiveType(dst).isConvertibleFrom(sw);
1048             } else {
1049                 // P->R must box and widen
1050                 return dst.isAssignableFrom(sw.wrapperType());
1051             }
1052         } else if (dst.isPrimitive()) {
1053             // any value can be dropped
1054             if (dst == void.class)  return true;
1055             Wrapper dw = Wrapper.forPrimitiveType(dst);
1056             // R->P must be able to unbox (from a dynamically chosen type) and widen
1057             // For example:
1058             //   Byte/Number/Comparable/Object -> dw:Byte -> byte.
1059             //   Character/Comparable/Object -> dw:Character -> char
1060             //   Boolean/Comparable/Object -> dw:Boolean -> boolean
1061             // This means that dw must be cast-compatible with src.
1062             if (src.isAssignableFrom(dw.wrapperType())) {
1063                 return true;
1064             }
1065             // The above does not work if the source reference is strongly typed
1066             // to a wrapper whose primitive must be widened.  For example:
1067             //   Byte -> unbox:byte -> short/int/long/float/double
1068             //   Character -> unbox:char -> int/long/float/double
1069             if (Wrapper.isWrapperType(src) &&
1070                 dw.isConvertibleFrom(Wrapper.forWrapperType(src))) {
1071                 // can unbox from src and then widen to dst
1072                 return true;
1073             }
1074             // We have already covered cases which arise due to runtime unboxing
1075             // of a reference type which covers several wrapper types:
1076             //   Object -> cast:Integer -> unbox:int -> long/float/double
1077             //   Serializable -> cast:Byte -> unbox:byte -> byte/short/int/long/float/double
1078             // An marginal case is Number -> dw:Character -> char, which would be OK if there were a
1079             // subclass of Number which wraps a value that can convert to char.
1080             // Since there is none, we don't need an extra check here to cover char or boolean.
1081             return false;
1082         } else {
1083             // R->R always works, since null is always valid dynamically
1084             return true;
1085         }
1086     }
1087 
1088     /// Queries which have to do with the bytecode architecture
1089 
1090     /** Reports the number of JVM stack slots required to invoke a method
1091      * of this type.  Note that (for historical reasons) the JVM requires
1092      * a second stack slot to pass long and double arguments.
1093      * So this method returns {@link #parameterCount() parameterCount} plus the
1094      * number of long and double parameters (if any).
1095      * <p>
1096      * This method is included for the benefit of applications that must
1097      * generate bytecodes that process method handles and invokedynamic.
1098      * @return the number of JVM stack slots for this type's parameters
1099      */
1100     /*non-public*/
1101     int parameterSlotCount() {
1102         return form.parameterSlotCount();
1103     }
1104 
1105     /*non-public*/
1106     Invokers invokers() {
1107         Invokers inv = invokers;
1108         if (inv != null)  return inv;
1109         invokers = inv = new Invokers(this);
1110         return inv;
1111     }
1112 
1113     /**
1114      * Finds or creates an instance of a method type, given the spelling of its bytecode descriptor.
1115      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
1116      * Any class or interface name embedded in the descriptor string will be
1117      * resolved by the given loader (or if it is null, on the system class loader).
1118      * <p>
1119      * Note that it is possible to encounter method types which cannot be
1120      * constructed by this method, because their component types are
1121      * not all reachable from a common class loader.
1122      * <p>
1123      * This method is included for the benefit of applications that must
1124      * generate bytecodes that process method handles and {@code invokedynamic}.
1125      * @param descriptor a bytecode-level type descriptor string "(T...)T"
1126      * @param loader the class loader in which to look up the types
1127      * @return a method type matching the bytecode-level type descriptor
1128      * @throws NullPointerException if the string is null
1129      * @throws IllegalArgumentException if the string is not well-formed
1130      * @throws TypeNotPresentException if a named type cannot be found
1131      * @throws SecurityException if the security manager is present and
1132      *         {@code loader} is {@code null} and the caller does not have the
1133      *         {@link RuntimePermission}{@code ("getClassLoader")}
1134      */
1135     public static MethodType fromMethodDescriptorString(String descriptor, ClassLoader loader)
1136         throws IllegalArgumentException, TypeNotPresentException
1137     {
1138         if (loader == null) {
1139             SecurityManager sm = System.getSecurityManager();
1140             if (sm != null) {
1141                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1142             }
1143         }
1144         return fromDescriptor(descriptor,
1145                               (loader == null) ? ClassLoader.getSystemClassLoader() : loader);
1146     }
1147 
1148     /**
1149      * Same as {@link #fromMethodDescriptorString(String, ClassLoader)}, but
1150      * {@code null} ClassLoader means the bootstrap loader is used here.
1151      * <p>
1152      * IMPORTANT: This method is preferable for JDK internal use as it more
1153      * correctly interprets {@code null} ClassLoader than
1154      * {@link #fromMethodDescriptorString(String, ClassLoader)}.
1155      * Use of this method also avoids early initialization issues when system
1156      * ClassLoader is not initialized yet.
1157      */
1158     static MethodType fromDescriptor(String descriptor, ClassLoader loader)
1159         throws IllegalArgumentException, TypeNotPresentException
1160     {
1161         if (!descriptor.startsWith("(") ||  // also generates NPE if needed
1162             descriptor.indexOf(')') < 0 ||
1163             descriptor.indexOf('.') >= 0)
1164             throw newIllegalArgumentException("not a method descriptor: "+descriptor);
1165         List<Class<?>> types = BytecodeDescriptor.parseMethod(descriptor, loader);
1166         Class<?> rtype = types.remove(types.size() - 1);
1167         Class<?>[] ptypes = listToArray(types);
1168         return makeImpl(rtype, ptypes, true);
1169     }
1170 
1171     /**
1172      * Returns a descriptor string for the method type.  This method
1173      * is equivalent to calling {@link #descriptorString() MethodType::descriptorString}.
1174      *
1175      * <p>
1176      * Note that this is not a strict inverse of {@link #fromMethodDescriptorString fromMethodDescriptorString}.
1177      * Two distinct classes which share a common name but have different class loaders
1178      * will appear identical when viewed within descriptor strings.
1179      * <p>
1180      * This method is included for the benefit of applications that must
1181      * generate bytecodes that process method handles and {@code invokedynamic}.
1182      * {@link #fromMethodDescriptorString(java.lang.String, java.lang.ClassLoader) fromMethodDescriptorString},
1183      * because the latter requires a suitable class loader argument.
1184      * @return the descriptor string for this method type
1185      * @jvms 4.3.3 Method Descriptors
1186      * @see <a href="#descriptor">Nominal Descriptor for {@code MethodType}</a>
1187      */
1188     public String toMethodDescriptorString() {
1189         String desc = methodDescriptor;
1190         if (desc == null) {
1191             desc = BytecodeDescriptor.unparseMethod(this.rtype, this.ptypes);
1192             methodDescriptor = desc;
1193         }
1194         return desc;
1195     }
1196 
1197     /**
1198      * Returns a descriptor string for this method type.
1199      *
1200      * <p>
1201      * If this method type can be <a href="#descriptor">described nominally</a>,
1202      * then the result is a method type descriptor (JVMS {@jvms 4.3.3}).
1203      * {@link MethodTypeDesc MethodTypeDesc} for this method type
1204      * can be produced by calling {@link MethodTypeDesc#ofDescriptor(String)
1205      * MethodTypeDesc::ofDescriptor} with the result descriptor string.
1206      * <p>
1207      * If this method type cannot be <a href="#descriptor">described nominally</a>
1208      * and the result is a string of the form:
1209      * <blockquote>{@code "(<parameter-descriptors>)<return-descriptor>"}</blockquote>
1210      * where {@code <parameter-descriptors>} is the concatenation of the
1211      * {@linkplain Class#descriptorString() descriptor string} of all
1212      * of the parameter types and the {@linkplain Class#descriptorString() descriptor string}
1213      * of the return type. No {@link java.lang.constant.MethodTypeDesc MethodTypeDesc}
1214      * can be produced from the result string.
1215      *
1216      * @return the descriptor string for this method type
1217      * @since 12
1218      * @jvms 4.3.3 Method Descriptors
1219      * @see <a href="#descriptor">Nominal Descriptor for {@code MethodType}</a>
1220      */
1221     @Override
1222     public String descriptorString() {
1223         return toMethodDescriptorString();
1224     }
1225 
1226     /*non-public*/
1227     static String toFieldDescriptorString(Class<?> cls) {
1228         return BytecodeDescriptor.unparse(cls);
1229     }
1230 
1231     /**
1232      * Returns a nominal descriptor for this instance, if one can be
1233      * constructed, or an empty {@link Optional} if one cannot be.
1234      *
1235      * @return An {@link Optional} containing the resulting nominal descriptor,
1236      * or an empty {@link Optional} if one cannot be constructed.
1237      * @since 12
1238      * @see <a href="#descriptor">Nominal Descriptor for {@code MethodType}</a>
1239      */
1240     @Override
1241     public Optional<MethodTypeDesc> describeConstable() {
1242         try {
1243             return Optional.of(MethodTypeDesc.of(returnType().describeConstable().orElseThrow(),
1244                                                  Stream.of(parameterArray())
1245                                                       .map(p -> p.describeConstable().orElseThrow())
1246                                                       .toArray(ClassDesc[]::new)));
1247         }
1248         catch (NoSuchElementException e) {
1249             return Optional.empty();
1250         }
1251     }
1252 
1253     /// Serialization.
1254 
1255     /**
1256      * There are no serializable fields for {@code MethodType}.
1257      */
1258     @java.io.Serial
1259     private static final java.io.ObjectStreamField[] serialPersistentFields = { };
1260 
1261     /**
1262      * Save the {@code MethodType} instance to a stream.
1263      *
1264      * @serialData
1265      * For portability, the serialized format does not refer to named fields.
1266      * Instead, the return type and parameter type arrays are written directly
1267      * from the {@code writeObject} method, using two calls to {@code s.writeObject}
1268      * as follows:
1269      * <blockquote><pre>{@code
1270 s.writeObject(this.returnType());
1271 s.writeObject(this.parameterArray());
1272      * }</pre></blockquote>
1273      * <p>
1274      * The deserialized field values are checked as if they were
1275      * provided to the factory method {@link #methodType(Class,Class[]) methodType}.
1276      * For example, null values, or {@code void} parameter types,
1277      * will lead to exceptions during deserialization.
1278      * @param s the stream to write the object to
1279      * @throws java.io.IOException if there is a problem writing the object
1280      */
1281     @java.io.Serial
1282     private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
1283         s.defaultWriteObject();  // requires serialPersistentFields to be an empty array
1284         s.writeObject(returnType());
1285         s.writeObject(parameterArray());
1286     }
1287 
1288     /**
1289      * Reconstitute the {@code MethodType} instance from a stream (that is,
1290      * deserialize it).
1291      * This instance is a scratch object with bogus final fields.
1292      * It provides the parameters to the factory method called by
1293      * {@link #readResolve readResolve}.
1294      * After that call it is discarded.
1295      * @param s the stream to read the object from
1296      * @throws java.io.IOException if there is a problem reading the object
1297      * @throws ClassNotFoundException if one of the component classes cannot be resolved
1298      * @see #readResolve
1299      * @see #writeObject
1300      */
1301     @java.io.Serial
1302     private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
1303         // Assign temporary defaults in case this object escapes
1304         MethodType_init(void.class, NO_PTYPES);
1305 
1306         s.defaultReadObject();  // requires serialPersistentFields to be an empty array
1307 
1308         Class<?>   returnType     = (Class<?>)   s.readObject();
1309         Class<?>[] parameterArray = (Class<?>[]) s.readObject();
1310         parameterArray = parameterArray.clone();  // make sure it is unshared
1311 
1312         // Assign deserialized values
1313         MethodType_init(returnType, parameterArray);
1314     }
1315 
1316     // Initialization of state for deserialization only
1317     private void MethodType_init(Class<?> rtype, Class<?>[] ptypes) {
1318         // In order to communicate these values to readResolve, we must
1319         // store them into the implementation-specific final fields.
1320         checkRtype(rtype);
1321         checkPtypes(ptypes);
1322         UNSAFE.putReference(this, OffsetHolder.rtypeOffset, rtype);
1323         UNSAFE.putReference(this, OffsetHolder.ptypesOffset, ptypes);
1324     }
1325 
1326     // Support for resetting final fields while deserializing. Implement Holder
1327     // pattern to make the rarely needed offset calculation lazy.
1328     private static class OffsetHolder {
1329         static final long rtypeOffset
1330                 = UNSAFE.objectFieldOffset(MethodType.class, "rtype");
1331 
1332         static final long ptypesOffset
1333                 = UNSAFE.objectFieldOffset(MethodType.class, "ptypes");
1334     }
1335 
1336     /**
1337      * Resolves and initializes a {@code MethodType} object
1338      * after serialization.
1339      * @return the fully initialized {@code MethodType} object
1340      */
1341     @java.io.Serial
1342     private Object readResolve() {
1343         // Do not use a trusted path for deserialization:
1344         //    return makeImpl(rtype, ptypes, true);
1345         // Verify all operands, and make sure ptypes is unshared:
1346         try {
1347             return methodType(rtype, ptypes);
1348         } finally {
1349             // Re-assign defaults in case this object escapes
1350             MethodType_init(void.class, NO_PTYPES);
1351         }
1352     }
1353 
1354     /**
1355      * Simple implementation of weak concurrent intern set.
1356      *
1357      * @param <T> interned type
1358      */
1359     private static class ConcurrentWeakInternSet<T> {
1360 
1361         private final ConcurrentMap<WeakEntry<T>, WeakEntry<T>> map;
1362         private final ReferenceQueue<T> stale;
1363 
1364         public ConcurrentWeakInternSet() {
1365             this.map = new ConcurrentHashMap<>(512);
1366             this.stale = new ReferenceQueue<>();
1367         }
1368 
1369         /**
1370          * Get the existing interned element.
1371          * This method returns null if no element is interned.
1372          *
1373          * @param elem element to look up
1374          * @return the interned element
1375          */
1376         public T get(T elem) {
1377             if (elem == null) throw new NullPointerException();
1378             expungeStaleElements();
1379 
1380             WeakEntry<T> value = map.get(elem);
1381             if (value != null) {
1382                 T res = value.get();
1383                 if (res != null) {
1384                     return res;
1385                 }
1386             }
1387             return null;
1388         }
1389 
1390         /**
1391          * Interns the element.
1392          * Always returns non-null element, matching the one in the intern set.
1393          * Under the race against another add(), it can return <i>different</i>
1394          * element, if another thread beats us to interning it.
1395          *
1396          * @param elem element to add
1397          * @return element that was actually added
1398          */
1399         public T add(T elem) {
1400             if (elem == null) throw new NullPointerException();
1401 
1402             // Playing double race here, and so spinloop is required.
1403             // First race is with two concurrent updaters.
1404             // Second race is with GC purging weak ref under our feet.
1405             // Hopefully, we almost always end up with a single pass.
1406             T interned;
1407             WeakEntry<T> e = new WeakEntry<>(elem, stale);
1408             do {
1409                 expungeStaleElements();
1410                 WeakEntry<T> exist = map.putIfAbsent(e, e);
1411                 interned = (exist == null) ? elem : exist.get();
1412             } while (interned == null);
1413             return interned;
1414         }
1415 
1416         private void expungeStaleElements() {
1417             Reference<? extends T> reference;
1418             while ((reference = stale.poll()) != null) {
1419                 map.remove(reference);
1420             }
1421         }
1422 
1423         private static class WeakEntry<T> extends WeakReference<T> {
1424 
1425             public final int hashcode;
1426 
1427             public WeakEntry(T key, ReferenceQueue<T> queue) {
1428                 super(key, queue);
1429                 hashcode = key.hashCode();
1430             }
1431 
1432             /**
1433              * This implementation returns {@code true} if {@code obj} is another
1434              * {@code WeakEntry} whose referent is equal to this referent, or
1435              * if {@code obj} is equal to the referent of this. This allows
1436              * lookups to be made without wrapping in a {@code WeakEntry}.
1437              *
1438              * @param obj the object to compare
1439              * @return true if {@code obj} is equal to this or the referent of this
1440              * @see MethodType#equals(Object)
1441              * @see Object#equals(Object)
1442              */
1443             @Override
1444             public boolean equals(Object obj) {
1445                 Object mine = get();
1446                 if (obj instanceof WeakEntry) {
1447                     Object that = ((WeakEntry) obj).get();
1448                     return (that == null || mine == null) ? (this == obj) : mine.equals(that);
1449                 }
1450                 return (mine == null) ? (obj == null) : mine.equals(obj);
1451             }
1452 
1453             @Override
1454             public int hashCode() {
1455                 return hashcode;
1456             }
1457 
1458         }
1459     }
1460 
1461 }