1 /*
   2  * Copyright (c) 2008, 2012, 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 sun.invoke.util.Wrapper;
  29 import java.lang.ref.WeakReference;
  30 import java.lang.ref.Reference;
  31 import java.lang.ref.ReferenceQueue;
  32 import java.util.Arrays;
  33 import java.util.Collections;
  34 import java.util.List;
  35 import java.util.concurrent.ConcurrentMap;
  36 import java.util.concurrent.ConcurrentHashMap;
  37 import sun.invoke.util.BytecodeDescriptor;
  38 import static java.lang.invoke.MethodHandleStatics.*;
  39 import sun.invoke.Stable;
  40 import sun.invoke.util.VerifyType;
  41 
  42 /**
  43  * A method type represents the arguments and return type accepted and
  44  * returned by a method handle, or the arguments and return type passed
  45  * and expected  by a method handle caller.  Method types must be properly
  46  * matched between a method handle and all its callers,
  47  * and the JVM's operations enforce this matching at, specifically
  48  * during calls to {@link MethodHandle#invokeExact MethodHandle.invokeExact}
  49  * and {@link MethodHandle#invoke MethodHandle.invoke}, and during execution
  50  * of {@code invokedynamic} instructions.
  51  * <p>
  52  * The structure is a return type accompanied by any number of parameter types.
  53  * The types (primitive, {@code void}, and reference) are represented by {@link Class} objects.
  54  * (For ease of exposition, we treat {@code void} as if it were a type.
  55  * In fact, it denotes the absence of a return type.)
  56  * <p>
  57  * All instances of {@code MethodType} are immutable.
  58  * Two instances are completely interchangeable if they compare equal.
  59  * Equality depends on pairwise correspondence of the return and parameter types and on nothing else.
  60  * <p>
  61  * This type can be created only by factory methods.
  62  * All factory methods may cache values, though caching is not guaranteed.
  63  * Some factory methods are static, while others are virtual methods which
  64  * modify precursor method types, e.g., by changing a selected parameter.
  65  * <p>
  66  * Factory methods which operate on groups of parameter types
  67  * are systematically presented in two versions, so that both Java arrays and
  68  * Java lists can be used to work with groups of parameter types.
  69  * The query methods {@code parameterArray} and {@code parameterList}
  70  * also provide a choice between arrays and lists.
  71  * <p>
  72  * {@code MethodType} objects are sometimes derived from bytecode instructions
  73  * such as {@code invokedynamic}, specifically from the type descriptor strings associated
  74  * with the instructions in a class file's constant pool.
  75  * <p>
  76  * Like classes and strings, method types can also be represented directly
  77  * in a class file's constant pool as constants.
  78  * A method type may be loaded by an {@code ldc} instruction which refers
  79  * to a suitable {@code CONSTANT_MethodType} constant pool entry.
  80  * The entry refers to a {@code CONSTANT_Utf8} spelling for the descriptor string.
  81  * For more details, see the <a href="package-summary.html#mtcon">package summary</a>.
  82  * <p>
  83  * When the JVM materializes a {@code MethodType} from a descriptor string,
  84  * all classes named in the descriptor must be accessible, and will be loaded.
  85  * (But the classes need not be initialized, as is the case with a {@code CONSTANT_Class}.)
  86  * This loading may occur at any time before the {@code MethodType} object is first derived.
  87  * @author John Rose, JSR 292 EG
  88  */
  89 public final
  90 class MethodType implements java.io.Serializable {
  91     private static final long serialVersionUID = 292L;  // {rtype, {ptype...}}
  92 
  93     // The rtype and ptypes fields define the structural identity of the method type:
  94     private final Class<?>   rtype;
  95     private final Class<?>[] ptypes;
  96 
  97     // The remaining fields are caches of various sorts:
  98     private @Stable MethodTypeForm form; // erased form, plus cached data about primitives
  99     private @Stable MethodType wrapAlt;  // alternative wrapped/unwrapped version
 100     private @Stable Invokers invokers;   // cache of handy higher-order adapters
 101 
 102     /**
 103      * Check the given parameters for validity and store them into the final fields.
 104      */
 105     private MethodType(Class<?> rtype, Class<?>[] ptypes) {
 106         checkRtype(rtype);
 107         checkPtypes(ptypes);
 108         this.rtype = rtype;
 109         this.ptypes = ptypes;
 110     }
 111 
 112     /*trusted*/ MethodTypeForm form() { return form; }
 113     /*trusted*/ Class<?> rtype() { return rtype; }
 114     /*trusted*/ Class<?>[] ptypes() { return ptypes; }
 115 
 116     void setForm(MethodTypeForm f) { form = f; }
 117 
 118     /** This number, mandated by the JVM spec as 255,
 119      *  is the maximum number of <em>slots</em>
 120      *  that any Java method can receive in its argument list.
 121      *  It limits both JVM signatures and method type objects.
 122      *  The longest possible invocation will look like
 123      *  {@code staticMethod(arg1, arg2, ..., arg255)} or
 124      *  {@code x.virtualMethod(arg1, arg2, ..., arg254)}.
 125      */
 126     /*non-public*/ static final int MAX_JVM_ARITY = 255;  // this is mandated by the JVM spec.
 127 
 128     /** This number is the maximum arity of a method handle, 254.
 129      *  It is derived from the absolute JVM-imposed arity by subtracting one,
 130      *  which is the slot occupied by the method handle itself at the
 131      *  beginning of the argument list used to invoke the method handle.
 132      *  The longest possible invocation will look like
 133      *  {@code mh.invoke(arg1, arg2, ..., arg254)}.
 134      */
 135     // Issue:  Should we allow MH.invokeWithArguments to go to the full 255?
 136     /*non-public*/ static final int MAX_MH_ARITY = MAX_JVM_ARITY-1;  // deduct one for mh receiver
 137 
 138     /** This number is the maximum arity of a method handle invoker, 253.
 139      *  It is derived from the absolute JVM-imposed arity by subtracting two,
 140      *  which are the slots occupied by invoke method handle, and the the
 141      *  target method handle, which are both at the beginning of the argument
 142      *  list used to invoke the target method handle.
 143      *  The longest possible invocation will look like
 144      *  {@code invokermh.invoke(targetmh, arg1, arg2, ..., arg253)}.
 145      */
 146     /*non-public*/ static final int MAX_MH_INVOKER_ARITY = MAX_MH_ARITY-1;  // deduct one more for invoker
 147 
 148     private static void checkRtype(Class<?> rtype) {
 149         rtype.equals(rtype);  // null check
 150     }
 151     private static int checkPtype(Class<?> ptype) {
 152         ptype.getClass();  //NPE
 153         if (ptype == void.class)
 154             throw newIllegalArgumentException("parameter type cannot be void");
 155         if (ptype == double.class || ptype == long.class)  return 1;
 156         return 0;
 157     }
 158     /** Return number of extra slots (count of long/double args). */
 159     private static int checkPtypes(Class<?>[] ptypes) {
 160         int slots = 0;
 161         for (Class<?> ptype : ptypes) {
 162             slots += checkPtype(ptype);
 163         }
 164         checkSlotCount(ptypes.length + slots);
 165         return slots;
 166     }
 167     static void checkSlotCount(int count) {
 168         assert((MAX_JVM_ARITY & (MAX_JVM_ARITY+1)) == 0);
 169         // MAX_JVM_ARITY must be power of 2 minus 1 for following code trick to work:
 170         if ((count & MAX_JVM_ARITY) != count)
 171             throw newIllegalArgumentException("bad parameter count "+count);
 172     }
 173     private static IndexOutOfBoundsException newIndexOutOfBoundsException(Object num) {
 174         if (num instanceof Integer)  num = "bad index: "+num;
 175         return new IndexOutOfBoundsException(num.toString());
 176     }
 177 
 178     static final ConcurrentWeakInternSet<MethodType> internTable = new ConcurrentWeakInternSet<>();
 179 
 180     static final Class<?>[] NO_PTYPES = {};
 181 
 182     /**
 183      * Finds or creates an instance of the given method type.
 184      * @param rtype  the return type
 185      * @param ptypes the parameter types
 186      * @return a method type with the given components
 187      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 188      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 189      */
 190     public static
 191     MethodType methodType(Class<?> rtype, Class<?>[] ptypes) {
 192         return makeImpl(rtype, ptypes, false);
 193     }
 194 
 195     /**
 196      * Finds or creates a method type with the given components.
 197      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 198      * @param rtype  the return type
 199      * @param ptypes the parameter types
 200      * @return a method type with the given components
 201      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 202      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 203      */
 204     public static
 205     MethodType methodType(Class<?> rtype, List<Class<?>> ptypes) {
 206         boolean notrust = false;  // random List impl. could return evil ptypes array
 207         return makeImpl(rtype, listToArray(ptypes), notrust);
 208     }
 209 
 210     private static Class<?>[] listToArray(List<Class<?>> ptypes) {
 211         // sanity check the size before the toArray call, since size might be huge
 212         checkSlotCount(ptypes.size());
 213         return ptypes.toArray(NO_PTYPES);
 214     }
 215 
 216     /**
 217      * Finds or creates a method type with the given components.
 218      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 219      * The leading parameter type is prepended to the remaining array.
 220      * @param rtype  the return type
 221      * @param ptype0 the first parameter type
 222      * @param ptypes the remaining parameter types
 223      * @return a method type with the given components
 224      * @throws NullPointerException if {@code rtype} or {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is null
 225      * @throws IllegalArgumentException if {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is {@code void.class}
 226      */
 227     public static
 228     MethodType methodType(Class<?> rtype, Class<?> ptype0, Class<?>... ptypes) {
 229         Class<?>[] ptypes1 = new Class<?>[1+ptypes.length];
 230         ptypes1[0] = ptype0;
 231         System.arraycopy(ptypes, 0, ptypes1, 1, ptypes.length);
 232         return makeImpl(rtype, ptypes1, true);
 233     }
 234 
 235     /**
 236      * Finds or creates a method type with the given components.
 237      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 238      * The resulting method has no parameter types.
 239      * @param rtype  the return type
 240      * @return a method type with the given return value
 241      * @throws NullPointerException if {@code rtype} is null
 242      */
 243     public static
 244     MethodType methodType(Class<?> rtype) {
 245         return makeImpl(rtype, NO_PTYPES, true);
 246     }
 247 
 248     /**
 249      * Finds or creates a method type with the given components.
 250      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 251      * The resulting method has the single given parameter type.
 252      * @param rtype  the return type
 253      * @param ptype0 the parameter type
 254      * @return a method type with the given return value and parameter type
 255      * @throws NullPointerException if {@code rtype} or {@code ptype0} is null
 256      * @throws IllegalArgumentException if {@code ptype0} is {@code void.class}
 257      */
 258     public static
 259     MethodType methodType(Class<?> rtype, Class<?> ptype0) {
 260         return makeImpl(rtype, new Class<?>[]{ ptype0 }, true);
 261     }
 262 
 263     /**
 264      * Finds or creates a method type with the given components.
 265      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 266      * The resulting method has the same parameter types as {@code ptypes},
 267      * and the specified return type.
 268      * @param rtype  the return type
 269      * @param ptypes the method type which supplies the parameter types
 270      * @return a method type with the given components
 271      * @throws NullPointerException if {@code rtype} or {@code ptypes} is null
 272      */
 273     public static
 274     MethodType methodType(Class<?> rtype, MethodType ptypes) {
 275         return makeImpl(rtype, ptypes.ptypes, true);
 276     }
 277 
 278     /**
 279      * Sole factory method to find or create an interned method type.
 280      * @param rtype desired return type
 281      * @param ptypes desired parameter types
 282      * @param trusted whether the ptypes can be used without cloning
 283      * @return the unique method type of the desired structure
 284      */
 285     /*trusted*/ static
 286     MethodType makeImpl(Class<?> rtype, Class<?>[] ptypes, boolean trusted) {
 287         if (ptypes.length == 0) {
 288             ptypes = NO_PTYPES; trusted = true;
 289         }
 290         MethodType mt1 = new MethodType(rtype, ptypes);
 291         MethodType mt0 = internTable.get(mt1);
 292         if (mt0 != null)
 293             return mt0;
 294         if (!trusted)
 295             // defensively copy the array passed in by the user
 296             mt1 = new MethodType(rtype, ptypes.clone());
 297         // promote the object to the Real Thing, and reprobe
 298         MethodTypeForm form = MethodTypeForm.findForm(mt1);
 299         mt1.form = form;
 300         return internTable.add(mt1);
 301     }
 302     private static final MethodType[] objectOnlyTypes = new MethodType[20];
 303 
 304     /**
 305      * Finds or creates a method type whose components are {@code Object} with an optional trailing {@code Object[]} array.
 306      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 307      * All parameters and the return type will be {@code Object},
 308      * except the final array parameter if any, which will be {@code Object[]}.
 309      * @param objectArgCount number of parameters (excluding the final array parameter if any)
 310      * @param finalArray whether there will be a trailing array parameter, of type {@code Object[]}
 311      * @return a generally applicable method type, for all calls of the given fixed argument count and a collected array of further arguments
 312      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255 (or 254, if {@code finalArray} is true)
 313      * @see #genericMethodType(int)
 314      */
 315     public static
 316     MethodType genericMethodType(int objectArgCount, boolean finalArray) {
 317         MethodType mt;
 318         checkSlotCount(objectArgCount);
 319         int ivarargs = (!finalArray ? 0 : 1);
 320         int ootIndex = objectArgCount*2 + ivarargs;
 321         if (ootIndex < objectOnlyTypes.length) {
 322             mt = objectOnlyTypes[ootIndex];
 323             if (mt != null)  return mt;
 324         }
 325         Class<?>[] ptypes = new Class<?>[objectArgCount + ivarargs];
 326         Arrays.fill(ptypes, Object.class);
 327         if (ivarargs != 0)  ptypes[objectArgCount] = Object[].class;
 328         mt = makeImpl(Object.class, ptypes, true);
 329         if (ootIndex < objectOnlyTypes.length) {
 330             objectOnlyTypes[ootIndex] = mt;     // cache it here also!
 331         }
 332         return mt;
 333     }
 334 
 335     /**
 336      * Finds or creates a method type whose components are all {@code Object}.
 337      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 338      * All parameters and the return type will be Object.
 339      * @param objectArgCount number of parameters
 340      * @return a generally applicable method type, for all calls of the given argument count
 341      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255
 342      * @see #genericMethodType(int, boolean)
 343      */
 344     public static
 345     MethodType genericMethodType(int objectArgCount) {
 346         return genericMethodType(objectArgCount, false);
 347     }
 348 
 349     /**
 350      * Finds or creates a method type with a single different parameter type.
 351      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 352      * @param num    the index (zero-based) of the parameter type to change
 353      * @param nptype a new parameter type to replace the old one with
 354      * @return the same type, except with the selected parameter changed
 355      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}
 356      * @throws IllegalArgumentException if {@code nptype} is {@code void.class}
 357      * @throws NullPointerException if {@code nptype} is null
 358      */
 359     public MethodType changeParameterType(int num, Class<?> nptype) {
 360         if (parameterType(num) == nptype)  return this;
 361         checkPtype(nptype);
 362         Class<?>[] nptypes = ptypes.clone();
 363         nptypes[num] = nptype;
 364         return makeImpl(rtype, nptypes, true);
 365     }
 366 
 367     /**
 368      * Finds or creates a method type with additional parameter types.
 369      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 370      * @param num    the position (zero-based) of the inserted parameter type(s)
 371      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 372      * @return the same type, except with the selected parameter(s) inserted
 373      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}
 374      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 375      *                                  or if the resulting method type would have more than 255 parameter slots
 376      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 377      */
 378     public MethodType insertParameterTypes(int num, Class<?>... ptypesToInsert) {
 379         int len = ptypes.length;
 380         if (num < 0 || num > len)
 381             throw newIndexOutOfBoundsException(num);
 382         int ins = checkPtypes(ptypesToInsert);
 383         checkSlotCount(parameterSlotCount() + ptypesToInsert.length + ins);
 384         int ilen = ptypesToInsert.length;
 385         if (ilen == 0)  return this;
 386         Class<?>[] nptypes = Arrays.copyOfRange(ptypes, 0, len+ilen);
 387         System.arraycopy(nptypes, num, nptypes, num+ilen, len-num);
 388         System.arraycopy(ptypesToInsert, 0, nptypes, num, ilen);
 389         return makeImpl(rtype, nptypes, true);
 390     }
 391 
 392     /**
 393      * Finds or creates a method type with additional parameter types.
 394      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 395      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list
 396      * @return the same type, except with the selected parameter(s) appended
 397      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 398      *                                  or if the resulting method type would have more than 255 parameter slots
 399      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 400      */
 401     public MethodType appendParameterTypes(Class<?>... ptypesToInsert) {
 402         return insertParameterTypes(parameterCount(), ptypesToInsert);
 403     }
 404 
 405     /**
 406      * Finds or creates a method type with additional parameter types.
 407      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 408      * @param num    the position (zero-based) of the inserted parameter type(s)
 409      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 410      * @return the same type, except with the selected parameter(s) inserted
 411      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}
 412      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 413      *                                  or if the resulting method type would have more than 255 parameter slots
 414      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 415      */
 416     public MethodType insertParameterTypes(int num, List<Class<?>> ptypesToInsert) {
 417         return insertParameterTypes(num, listToArray(ptypesToInsert));
 418     }
 419 
 420     /**
 421      * Finds or creates a method type with additional parameter types.
 422      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 423      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list
 424      * @return the same type, except with the selected parameter(s) appended
 425      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 426      *                                  or if the resulting method type would have more than 255 parameter slots
 427      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 428      */
 429     public MethodType appendParameterTypes(List<Class<?>> ptypesToInsert) {
 430         return insertParameterTypes(parameterCount(), ptypesToInsert);
 431     }
 432 
 433      /**
 434      * Finds or creates a method type with modified parameter types.
 435      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 436      * @param start  the position (zero-based) of the first replaced parameter type(s)
 437      * @param end    the position (zero-based) after the last replaced parameter type(s)
 438      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 439      * @return the same type, except with the selected parameter(s) replaced
 440      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}
 441      *                                  or if {@code end} is negative or greater than {@code parameterCount()}
 442      *                                  or if {@code start} is greater than {@code end}
 443      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 444      *                                  or if the resulting method type would have more than 255 parameter slots
 445      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 446      */
 447     /*non-public*/ MethodType replaceParameterTypes(int start, int end, Class<?>... ptypesToInsert) {
 448         if (start == end)
 449             return insertParameterTypes(start, ptypesToInsert);
 450         int len = ptypes.length;
 451         if (!(0 <= start && start <= end && end <= len))
 452             throw newIndexOutOfBoundsException("start="+start+" end="+end);
 453         int ilen = ptypesToInsert.length;
 454         if (ilen == 0)
 455             return dropParameterTypes(start, end);
 456         return dropParameterTypes(start, end).insertParameterTypes(start, ptypesToInsert);
 457     }
 458 
 459     /**
 460      * Finds or creates a method type with some parameter types omitted.
 461      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 462      * @param start  the index (zero-based) of the first parameter type to remove
 463      * @param end    the index (greater than {@code start}) of the first parameter type after not to remove
 464      * @return the same type, except with the selected parameter(s) removed
 465      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}
 466      *                                  or if {@code end} is negative or greater than {@code parameterCount()}
 467      *                                  or if {@code start} is greater than {@code end}
 468      */
 469     public MethodType dropParameterTypes(int start, int end) {
 470         int len = ptypes.length;
 471         if (!(0 <= start && start <= end && end <= len))
 472             throw newIndexOutOfBoundsException("start="+start+" end="+end);
 473         if (start == end)  return this;
 474         Class<?>[] nptypes;
 475         if (start == 0) {
 476             if (end == len) {
 477                 // drop all parameters
 478                 nptypes = NO_PTYPES;
 479             } else {
 480                 // drop initial parameter(s)
 481                 nptypes = Arrays.copyOfRange(ptypes, end, len);
 482             }
 483         } else {
 484             if (end == len) {
 485                 // drop trailing parameter(s)
 486                 nptypes = Arrays.copyOfRange(ptypes, 0, start);
 487             } else {
 488                 int tail = len - end;
 489                 nptypes = Arrays.copyOfRange(ptypes, 0, start + tail);
 490                 System.arraycopy(ptypes, end, nptypes, start, tail);
 491             }
 492         }
 493         return makeImpl(rtype, nptypes, true);
 494     }
 495 
 496     /**
 497      * Finds or creates a method type with a different return type.
 498      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 499      * @param nrtype a return parameter type to replace the old one with
 500      * @return the same type, except with the return type change
 501      * @throws NullPointerException if {@code nrtype} is null
 502      */
 503     public MethodType changeReturnType(Class<?> nrtype) {
 504         if (returnType() == nrtype)  return this;
 505         return makeImpl(nrtype, ptypes, true);
 506     }
 507 
 508     /**
 509      * Reports if this type contains a primitive argument or return value.
 510      * The return type {@code void} counts as a primitive.
 511      * @return true if any of the types are primitives
 512      */
 513     public boolean hasPrimitives() {
 514         return form.hasPrimitives();
 515     }
 516 
 517     /**
 518      * Reports if this type contains a wrapper argument or return value.
 519      * Wrappers are types which box primitive values, such as {@link Integer}.
 520      * The reference type {@code java.lang.Void} counts as a wrapper,
 521      * if it occurs as a return type.
 522      * @return true if any of the types are wrappers
 523      */
 524     public boolean hasWrappers() {
 525         return unwrap() != this;
 526     }
 527 
 528     /**
 529      * Erases all reference types to {@code Object}.
 530      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 531      * All primitive types (including {@code void}) will remain unchanged.
 532      * @return a version of the original type with all reference types replaced
 533      */
 534     public MethodType erase() {
 535         return form.erasedType();
 536     }
 537 
 538     /**
 539      * Erases all reference types to {@code Object}, and all subword types to {@code int}.
 540      * This is the reduced type polymorphism used by private methods
 541      * such as {@link MethodHandle#invokeBasic invokeBasic}.
 542      * @return a version of the original type with all reference and subword types replaced
 543      */
 544     /*non-public*/ MethodType basicType() {
 545         return form.basicType();
 546     }
 547 
 548     /**
 549      * @return a version of the original type with MethodHandle prepended as the first argument
 550      */
 551     /*non-public*/ MethodType invokerType() {
 552         return insertParameterTypes(0, MethodHandle.class);
 553     }
 554 
 555     /**
 556      * Converts all types, both reference and primitive, to {@code Object}.
 557      * Convenience method for {@link #genericMethodType(int) genericMethodType}.
 558      * The expression {@code type.wrap().erase()} produces the same value
 559      * as {@code type.generic()}.
 560      * @return a version of the original type with all types replaced
 561      */
 562     public MethodType generic() {
 563         return genericMethodType(parameterCount());
 564     }
 565 
 566     /**
 567      * Converts all primitive types to their corresponding wrapper types.
 568      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 569      * All reference types (including wrapper types) will remain unchanged.
 570      * A {@code void} return type is changed to the type {@code java.lang.Void}.
 571      * The expression {@code type.wrap().erase()} produces the same value
 572      * as {@code type.generic()}.
 573      * @return a version of the original type with all primitive types replaced
 574      */
 575     public MethodType wrap() {
 576         return hasPrimitives() ? wrapWithPrims(this) : this;
 577     }
 578 
 579     /**
 580      * Converts all wrapper types to their corresponding primitive types.
 581      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 582      * All primitive types (including {@code void}) will remain unchanged.
 583      * A return type of {@code java.lang.Void} is changed to {@code void}.
 584      * @return a version of the original type with all wrapper types replaced
 585      */
 586     public MethodType unwrap() {
 587         MethodType noprims = !hasPrimitives() ? this : wrapWithPrims(this);
 588         return unwrapWithNoPrims(noprims);
 589     }
 590 
 591     private static MethodType wrapWithPrims(MethodType pt) {
 592         assert(pt.hasPrimitives());
 593         MethodType wt = pt.wrapAlt;
 594         if (wt == null) {
 595             // fill in lazily
 596             wt = MethodTypeForm.canonicalize(pt, MethodTypeForm.WRAP, MethodTypeForm.WRAP);
 597             assert(wt != null);
 598             pt.wrapAlt = wt;
 599         }
 600         return wt;
 601     }
 602 
 603     private static MethodType unwrapWithNoPrims(MethodType wt) {
 604         assert(!wt.hasPrimitives());
 605         MethodType uwt = wt.wrapAlt;
 606         if (uwt == null) {
 607             // fill in lazily
 608             uwt = MethodTypeForm.canonicalize(wt, MethodTypeForm.UNWRAP, MethodTypeForm.UNWRAP);
 609             if (uwt == null)
 610                 uwt = wt;    // type has no wrappers or prims at all
 611             wt.wrapAlt = uwt;
 612         }
 613         return uwt;
 614     }
 615 
 616     /**
 617      * Returns the parameter type at the specified index, within this method type.
 618      * @param num the index (zero-based) of the desired parameter type
 619      * @return the selected parameter type
 620      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}
 621      */
 622     public Class<?> parameterType(int num) {
 623         return ptypes[num];
 624     }
 625     /**
 626      * Returns the number of parameter types in this method type.
 627      * @return the number of parameter types
 628      */
 629     public int parameterCount() {
 630         return ptypes.length;
 631     }
 632     /**
 633      * Returns the return type of this method type.
 634      * @return the return type
 635      */
 636     public Class<?> returnType() {
 637         return rtype;
 638     }
 639 
 640     /**
 641      * Presents the parameter types as a list (a convenience method).
 642      * The list will be immutable.
 643      * @return the parameter types (as an immutable list)
 644      */
 645     public List<Class<?>> parameterList() {
 646         return Collections.unmodifiableList(Arrays.asList(ptypes));
 647     }
 648 
 649     /*non-public*/ Class<?> lastParameterType() {
 650         int len = ptypes.length;
 651         return len == 0 ? void.class : ptypes[len-1];
 652     }
 653 
 654     /**
 655      * Presents the parameter types as an array (a convenience method).
 656      * Changes to the array will not result in changes to the type.
 657      * @return the parameter types (as a fresh copy if necessary)
 658      */
 659     public Class<?>[] parameterArray() {
 660         return ptypes.clone();
 661     }
 662 
 663     /**
 664      * Compares the specified object with this type for equality.
 665      * That is, it returns <tt>true</tt> if and only if the specified object
 666      * is also a method type with exactly the same parameters and return type.
 667      * @param x object to compare
 668      * @see Object#equals(Object)
 669      */
 670     @Override
 671     public boolean equals(Object x) {
 672         return this == x || x instanceof MethodType && equals((MethodType)x);
 673     }
 674 
 675     private boolean equals(MethodType that) {
 676         return this.rtype == that.rtype
 677             && Arrays.equals(this.ptypes, that.ptypes);
 678     }
 679 
 680     /**
 681      * Returns the hash code value for this method type.
 682      * It is defined to be the same as the hashcode of a List
 683      * whose elements are the return type followed by the
 684      * parameter types.
 685      * @return the hash code value for this method type
 686      * @see Object#hashCode()
 687      * @see #equals(Object)
 688      * @see List#hashCode()
 689      */
 690     @Override
 691     public int hashCode() {
 692       int hashCode = 31 + rtype.hashCode();
 693       for (Class<?> ptype : ptypes)
 694           hashCode = 31*hashCode + ptype.hashCode();
 695       return hashCode;
 696     }
 697 
 698     /**
 699      * Returns a string representation of the method type,
 700      * of the form {@code "(PT0,PT1...)RT"}.
 701      * The string representation of a method type is a
 702      * parenthesis enclosed, comma separated list of type names,
 703      * followed immediately by the return type.
 704      * <p>
 705      * Each type is represented by its
 706      * {@link java.lang.Class#getSimpleName simple name}.
 707      */
 708     @Override
 709     public String toString() {
 710         StringBuilder sb = new StringBuilder();
 711         sb.append("(");
 712         for (int i = 0; i < ptypes.length; i++) {
 713             if (i > 0)  sb.append(",");
 714             sb.append(ptypes[i].getSimpleName());
 715         }
 716         sb.append(")");
 717         sb.append(rtype.getSimpleName());
 718         return sb.toString();
 719     }
 720 
 721 
 722     /*non-public*/
 723     boolean isViewableAs(MethodType newType) {
 724         if (!VerifyType.isNullConversion(returnType(), newType.returnType()))
 725             return false;
 726         int argc = parameterCount();
 727         if (argc != newType.parameterCount())
 728             return false;
 729         for (int i = 0; i < argc; i++) {
 730             if (!VerifyType.isNullConversion(newType.parameterType(i), parameterType(i)))
 731                 return false;
 732         }
 733         return true;
 734     }
 735     /*non-public*/
 736     boolean isCastableTo(MethodType newType) {
 737         int argc = parameterCount();
 738         if (argc != newType.parameterCount())
 739             return false;
 740         return true;
 741     }
 742     /*non-public*/
 743     boolean isConvertibleTo(MethodType newType) {
 744         if (!canConvert(returnType(), newType.returnType()))
 745             return false;
 746         int argc = parameterCount();
 747         if (argc != newType.parameterCount())
 748             return false;
 749         for (int i = 0; i < argc; i++) {
 750             if (!canConvert(newType.parameterType(i), parameterType(i)))
 751                 return false;
 752         }
 753         return true;
 754     }
 755     /*non-public*/
 756     static boolean canConvert(Class<?> src, Class<?> dst) {
 757         // short-circuit a few cases:
 758         if (src == dst || dst == Object.class)  return true;
 759         // the remainder of this logic is documented in MethodHandle.asType
 760         if (src.isPrimitive()) {
 761             // can force void to an explicit null, a la reflect.Method.invoke
 762             // can also force void to a primitive zero, by analogy
 763             if (src == void.class)  return true;  //or !dst.isPrimitive()?
 764             Wrapper sw = Wrapper.forPrimitiveType(src);
 765             if (dst.isPrimitive()) {
 766                 // P->P must widen
 767                 return Wrapper.forPrimitiveType(dst).isConvertibleFrom(sw);
 768             } else {
 769                 // P->R must box and widen
 770                 return dst.isAssignableFrom(sw.wrapperType());
 771             }
 772         } else if (dst.isPrimitive()) {
 773             // any value can be dropped
 774             if (dst == void.class)  return true;
 775             Wrapper dw = Wrapper.forPrimitiveType(dst);
 776             // R->P must be able to unbox (from a dynamically chosen type) and widen
 777             // For example:
 778             //   Byte/Number/Comparable/Object -> dw:Byte -> byte.
 779             //   Character/Comparable/Object -> dw:Character -> char
 780             //   Boolean/Comparable/Object -> dw:Boolean -> boolean
 781             // This means that dw must be cast-compatible with src.
 782             if (src.isAssignableFrom(dw.wrapperType())) {
 783                 return true;
 784             }
 785             // The above does not work if the source reference is strongly typed
 786             // to a wrapper whose primitive must be widened.  For example:
 787             //   Byte -> unbox:byte -> short/int/long/float/double
 788             //   Character -> unbox:char -> int/long/float/double
 789             if (Wrapper.isWrapperType(src) &&
 790                 dw.isConvertibleFrom(Wrapper.forWrapperType(src))) {
 791                 // can unbox from src and then widen to dst
 792                 return true;
 793             }
 794             // We have already covered cases which arise due to runtime unboxing
 795             // of a reference type which covers several wrapper types:
 796             //   Object -> cast:Integer -> unbox:int -> long/float/double
 797             //   Serializable -> cast:Byte -> unbox:byte -> byte/short/int/long/float/double
 798             // An marginal case is Number -> dw:Character -> char, which would be OK if there were a
 799             // subclass of Number which wraps a value that can convert to char.
 800             // Since there is none, we don't need an extra check here to cover char or boolean.
 801             return false;
 802         } else {
 803             // R->R always works, since null is always valid dynamically
 804             return true;
 805         }
 806     }
 807 
 808     /// Queries which have to do with the bytecode architecture
 809 
 810     /** Reports the number of JVM stack slots required to invoke a method
 811      * of this type.  Note that (for historical reasons) the JVM requires
 812      * a second stack slot to pass long and double arguments.
 813      * So this method returns {@link #parameterCount() parameterCount} plus the
 814      * number of long and double parameters (if any).
 815      * <p>
 816      * This method is included for the benfit of applications that must
 817      * generate bytecodes that process method handles and invokedynamic.
 818      * @return the number of JVM stack slots for this type's parameters
 819      */
 820     /*non-public*/ int parameterSlotCount() {
 821         return form.parameterSlotCount();
 822     }
 823 
 824     /*non-public*/ Invokers invokers() {
 825         Invokers inv = invokers;
 826         if (inv != null)  return inv;
 827         invokers = inv = new Invokers(this);
 828         return inv;
 829     }
 830 
 831     /** Reports the number of JVM stack slots which carry all parameters including and after
 832      * the given position, which must be in the range of 0 to
 833      * {@code parameterCount} inclusive.  Successive parameters are
 834      * more shallowly stacked, and parameters are indexed in the bytecodes
 835      * according to their trailing edge.  Thus, to obtain the depth
 836      * in the outgoing call stack of parameter {@code N}, obtain
 837      * the {@code parameterSlotDepth} of its trailing edge
 838      * at position {@code N+1}.
 839      * <p>
 840      * Parameters of type {@code long} and {@code double} occupy
 841      * two stack slots (for historical reasons) and all others occupy one.
 842      * Therefore, the number returned is the number of arguments
 843      * <em>including</em> and <em>after</em> the given parameter,
 844      * <em>plus</em> the number of long or double arguments
 845      * at or after after the argument for the given parameter.
 846      * <p>
 847      * This method is included for the benfit of applications that must
 848      * generate bytecodes that process method handles and invokedynamic.
 849      * @param num an index (zero-based, inclusive) within the parameter types
 850      * @return the index of the (shallowest) JVM stack slot transmitting the
 851      *         given parameter
 852      * @throws IllegalArgumentException if {@code num} is negative or greater than {@code parameterCount()}
 853      */
 854     /*non-public*/ int parameterSlotDepth(int num) {
 855         if (num < 0 || num > ptypes.length)
 856             parameterType(num);  // force a range check
 857         return form.parameterToArgSlot(num-1);
 858     }
 859 
 860     /** Reports the number of JVM stack slots required to receive a return value
 861      * from a method of this type.
 862      * If the {@link #returnType() return type} is void, it will be zero,
 863      * else if the return type is long or double, it will be two, else one.
 864      * <p>
 865      * This method is included for the benfit of applications that must
 866      * generate bytecodes that process method handles and invokedynamic.
 867      * @return the number of JVM stack slots (0, 1, or 2) for this type's return value
 868      * Will be removed for PFD.
 869      */
 870     /*non-public*/ int returnSlotCount() {
 871         return form.returnSlotCount();
 872     }
 873 
 874     /**
 875      * Finds or creates an instance of a method type, given the spelling of its bytecode descriptor.
 876      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 877      * Any class or interface name embedded in the descriptor string
 878      * will be resolved by calling {@link ClassLoader#loadClass(java.lang.String)}
 879      * on the given loader (or if it is null, on the system class loader).
 880      * <p>
 881      * Note that it is possible to encounter method types which cannot be
 882      * constructed by this method, because their component types are
 883      * not all reachable from a common class loader.
 884      * <p>
 885      * This method is included for the benfit of applications that must
 886      * generate bytecodes that process method handles and {@code invokedynamic}.
 887      * @param descriptor a bytecode-level type descriptor string "(T...)T"
 888      * @param loader the class loader in which to look up the types
 889      * @return a method type matching the bytecode-level type descriptor
 890      * @throws NullPointerException if the string is null
 891      * @throws IllegalArgumentException if the string is not well-formed
 892      * @throws TypeNotPresentException if a named type cannot be found
 893      */
 894     public static MethodType fromMethodDescriptorString(String descriptor, ClassLoader loader)
 895         throws IllegalArgumentException, TypeNotPresentException
 896     {
 897         if (!descriptor.startsWith("(") ||  // also generates NPE if needed
 898             descriptor.indexOf(')') < 0 ||
 899             descriptor.indexOf('.') >= 0)
 900             throw new IllegalArgumentException("not a method descriptor: "+descriptor);
 901         List<Class<?>> types = BytecodeDescriptor.parseMethod(descriptor, loader);
 902         Class<?> rtype = types.remove(types.size() - 1);
 903         checkSlotCount(types.size());
 904         Class<?>[] ptypes = listToArray(types);
 905         return makeImpl(rtype, ptypes, true);
 906     }
 907 
 908     /**
 909      * Produces a bytecode descriptor representation of the method type.
 910      * <p>
 911      * Note that this is not a strict inverse of {@link #fromMethodDescriptorString fromMethodDescriptorString}.
 912      * Two distinct classes which share a common name but have different class loaders
 913      * will appear identical when viewed within descriptor strings.
 914      * <p>
 915      * This method is included for the benfit of applications that must
 916      * generate bytecodes that process method handles and {@code invokedynamic}.
 917      * {@link #fromMethodDescriptorString(java.lang.String, java.lang.ClassLoader) fromMethodDescriptorString},
 918      * because the latter requires a suitable class loader argument.
 919      * @return the bytecode type descriptor representation
 920      */
 921     public String toMethodDescriptorString() {
 922         return BytecodeDescriptor.unparse(this);
 923     }
 924 
 925     /*non-public*/ static String toFieldDescriptorString(Class<?> cls) {
 926         return BytecodeDescriptor.unparse(cls);
 927     }
 928 
 929     /// Serialization.
 930 
 931     /**
 932      * There are no serializable fields for {@code MethodType}.
 933      */
 934     private static final java.io.ObjectStreamField[] serialPersistentFields = { };
 935 
 936     /**
 937      * Save the {@code MethodType} instance to a stream.
 938      *
 939      * @serialData
 940      * For portability, the serialized format does not refer to named fields.
 941      * Instead, the return type and parameter type arrays are written directly
 942      * from the {@code writeObject} method, using two calls to {@code s.writeObject}
 943      * as follows:
 944      * <blockquote><pre>
 945 s.writeObject(this.returnType());
 946 s.writeObject(this.parameterArray());
 947      * </pre></blockquote>
 948      * <p>
 949      * The deserialized field values are checked as if they were
 950      * provided to the factory method {@link #methodType(Class,Class[]) methodType}.
 951      * For example, null values, or {@code void} parameter types,
 952      * will lead to exceptions during deserialization.
 953      * @param s the stream to write the object to
 954      * @throws java.io.IOException if there is a problem writing the object
 955      */
 956     private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
 957         s.defaultWriteObject();  // requires serialPersistentFields to be an empty array
 958         s.writeObject(returnType());
 959         s.writeObject(parameterArray());
 960     }
 961 
 962     /**
 963      * Reconstitute the {@code MethodType} instance from a stream (that is,
 964      * deserialize it).
 965      * This instance is a scratch object with bogus final fields.
 966      * It provides the parameters to the factory method called by
 967      * {@link #readResolve readResolve}.
 968      * After that call it is discarded.
 969      * @param s the stream to read the object from
 970      * @throws java.io.IOException if there is a problem reading the object
 971      * @throws ClassNotFoundException if one of the component classes cannot be resolved
 972      * @see #MethodType()
 973      * @see #readResolve
 974      * @see #writeObject
 975      */
 976     private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
 977         s.defaultReadObject();  // requires serialPersistentFields to be an empty array
 978 
 979         Class<?>   returnType     = (Class<?>)   s.readObject();
 980         Class<?>[] parameterArray = (Class<?>[]) s.readObject();
 981 
 982         // Probably this object will never escape, but let's check
 983         // the field values now, just to be sure.
 984         checkRtype(returnType);
 985         checkPtypes(parameterArray);
 986 
 987         parameterArray = parameterArray.clone();  // make sure it is unshared
 988         MethodType_init(returnType, parameterArray);
 989     }
 990 
 991     /**
 992      * For serialization only.
 993      * Sets the final fields to null, pending {@code Unsafe.putObject}.
 994      */
 995     private MethodType() {
 996         this.rtype = null;
 997         this.ptypes = null;
 998     }
 999     private void MethodType_init(Class<?> rtype, Class<?>[] ptypes) {
1000         // In order to communicate these values to readResolve, we must
1001         // store them into the implementation-specific final fields.
1002         checkRtype(rtype);
1003         checkPtypes(ptypes);
1004         UNSAFE.putObject(this, rtypeOffset, rtype);
1005         UNSAFE.putObject(this, ptypesOffset, ptypes);
1006     }
1007 
1008     // Support for resetting final fields while deserializing
1009     private static final long rtypeOffset, ptypesOffset;
1010     static {
1011         try {
1012             rtypeOffset = UNSAFE.objectFieldOffset
1013                 (MethodType.class.getDeclaredField("rtype"));
1014             ptypesOffset = UNSAFE.objectFieldOffset
1015                 (MethodType.class.getDeclaredField("ptypes"));
1016         } catch (Exception ex) {
1017             throw new Error(ex);
1018         }
1019     }
1020 
1021     /**
1022      * Resolves and initializes a {@code MethodType} object
1023      * after serialization.
1024      * @return the fully initialized {@code MethodType} object
1025      */
1026     private Object readResolve() {
1027         // Do not use a trusted path for deserialization:
1028         //return makeImpl(rtype, ptypes, true);
1029         // Verify all operands, and make sure ptypes is unshared:
1030         return methodType(rtype, ptypes);
1031     }
1032 
1033     /**
1034      * Simple implementation of weak concurrent intern set.
1035      *
1036      * @param <T> interned type
1037      */
1038     private static class ConcurrentWeakInternSet<T> {
1039 
1040         private final ConcurrentMap<WeakEntry<T>, WeakEntry<T>> map;
1041         private final ReferenceQueue<T> stale;
1042 
1043         public ConcurrentWeakInternSet() {
1044             this.map = new ConcurrentHashMap<>();
1045             this.stale = new ReferenceQueue<>();
1046         }
1047 
1048         /**
1049          * Get the existing interned element.
1050          * This method returns null if no element is interned.
1051          *
1052          * @param elem element to look up
1053          * @return the interned element
1054          */
1055         public T get(T elem) {
1056             if (elem == null) throw new NullPointerException();
1057             expungeStaleElements();
1058 
1059             WeakEntry<T> value = map.get(new WeakEntry<>(elem));
1060             if (value != null) {
1061                 T res = value.get();
1062                 if (res != null) {
1063                     return res;
1064                 }
1065             }
1066             return null;
1067         }
1068 
1069         /**
1070          * Interns the element.
1071          * Always returns non-null element, matching the one in the intern set.
1072          * Under the race against another add(), it can return <i>different</i>
1073          * element, if another thread beats us to interning it.
1074          *
1075          * @param elem element to add
1076          * @return element that was actually added
1077          */
1078         public T add(T elem) {
1079             if (elem == null) throw new NullPointerException();
1080 
1081             // Playing double race here, and so spinloop is required.
1082             // First race is with two concurrent updaters.
1083             // Second race is with GC purging weak ref under our feet.
1084             // Hopefully, we almost always end up with a single pass.
1085             T interned;
1086             WeakEntry<T> e = new WeakEntry<>(elem, stale);
1087             do {
1088                 expungeStaleElements();
1089                 WeakEntry<T> exist = map.putIfAbsent(e, e);
1090                 interned = (exist == null) ? elem : exist.get();
1091             } while (interned == null);
1092             return interned;
1093         }
1094 
1095         private void expungeStaleElements() {
1096             Reference<? extends T> reference;
1097             while ((reference = stale.poll()) != null) {
1098                 map.remove(reference);
1099             }
1100         }
1101 
1102         private static class WeakEntry<T> extends WeakReference<T> {
1103 
1104             public final int hashcode;
1105 
1106             public WeakEntry(T key, ReferenceQueue<T> queue) {
1107                 super(key, queue);
1108                 hashcode = key.hashCode();
1109             }
1110 
1111             public WeakEntry(T key) {
1112                 super(key);
1113                 hashcode = key.hashCode();
1114             }
1115 
1116             @Override
1117             public boolean equals(Object obj) {
1118                 if (obj instanceof WeakEntry) {
1119                     Object that = ((WeakEntry) obj).get();
1120                     Object mine = get();
1121                     return (that == null || mine == null) ? (this == obj) : mine.equals(that);
1122                 }
1123                 return false;
1124             }
1125 
1126             @Override
1127             public int hashCode() {
1128                 return hashcode;
1129             }
1130 
1131         }
1132     }
1133 
1134 }