1 /* 2 * Copyright (c) 2023, 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 jdk.internal.util; 27 28 import java.lang.ref.ReferenceQueue; 29 import java.lang.ref.WeakReference; 30 import java.util.Objects; 31 32 /** 33 * {@link WeakReference} wrapper key for entries in the backing map. 34 * 35 * @param <T> key type 36 * 37 * @since 21 38 */ 39 final class WeakReferenceKey<T> extends WeakReference<T> implements ReferenceKey<T> { 40 /** 41 * Saved hashcode of the key. Used when {@link WeakReference} is 42 * null. 43 */ 44 private final int hashcode; 45 46 /** 47 * Package-Protected constructor. 48 * 49 * @param key unwrapped key value 50 * @param queue reference queue 51 */ WeakReferenceKey(T key, ReferenceQueue<T> queue)52 WeakReferenceKey(T key, ReferenceQueue<T> queue) { 53 super(key, queue); 54 this.hashcode = Objects.hashCode(key); 55 } 56 57 /** 58 * Cleanup unused key. No need to enqueue since the key did not make it 59 * into the map. 60 */ 61 @Override unused()62 public void unused() { 63 clear(); 64 } 65 66 @Override equals(Object obj)67 public boolean equals(Object obj) { 68 // Necessary when removing a null reference 69 if (obj == this) { 70 return true; 71 } 72 // Necessary when comparing an unwrapped key 73 if (obj instanceof ReferenceKey<?> key) { 74 obj = key.get(); 75 } 76 // Note: refersTo is insufficient since keys require equivalence. 77 // refersTo would also require a cast to type T. 78 return Objects.equals(get(), obj); 79 } 80 81 @Override hashCode()82 public int hashCode() { 83 // Use saved hashcode 84 return hashcode; 85 } 86 87 @Override toString()88 public String toString() { 89 return this.getClass().getCanonicalName() + "#" + System.identityHashCode(this); 90 } 91 } 92