1f33eae7e84eb6d3b0f4e86b59605bb3de73009f3Elliott Hughes/* 2adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Licensed to the Apache Software Foundation (ASF) under one or more 3adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * contributor license agreements. See the NOTICE file distributed with 4adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * this work for additional information regarding copyright ownership. 5adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * The ASF licenses this file to You under the Apache License, Version 2.0 6adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * (the "License"); you may not use this file except in compliance with 7adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * the License. You may obtain a copy of the License at 8f33eae7e84eb6d3b0f4e86b59605bb3de73009f3Elliott Hughes * 9adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * http://www.apache.org/licenses/LICENSE-2.0 10f33eae7e84eb6d3b0f4e86b59605bb3de73009f3Elliott Hughes * 11adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Unless required by applicable law or agreed to in writing, software 12adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * distributed under the License is distributed on an "AS IS" BASIS, 13adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * See the License for the specific language governing permissions and 15adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * limitations under the License. 16adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project */ 17adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project/* 18adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Copyright (C) 2008 The Android Open Source Project 19adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * 20adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Licensed under the Apache License, Version 2.0 (the "License"); 21adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * you may not use this file except in compliance with the License. 22adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * You may obtain a copy of the License at 23adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * 24adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * http://www.apache.org/licenses/LICENSE-2.0 25adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * 26adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Unless required by applicable law or agreed to in writing, software 27adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * distributed under the License is distributed on an "AS IS" BASIS, 28adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 29adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * See the License for the specific language governing permissions and 30adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * limitations under the License. 31adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project */ 32adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project 33adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Projectpackage java.lang.ref; 34adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project 35adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project/** 36adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Implements a phantom reference, which is the weakest of the three types of 37adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * references. Once the garbage collector decides that an object {@code obj} is 38016a87c7952b25eededfc222615e25a5a72bcddaScott Main * phantom-reachable, it is being enqueued 39adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * on the corresponding queue, but its referent is not cleared. That is, the 40adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * reference queue of the phantom reference must explicitly be processed by some 41adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * application code. As a consequence, a phantom reference that is not 42adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * registered with any reference queue does not make any sense. 43adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * <p> 44adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Phantom references are useful for implementing cleanup operations that are 45adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * necessary before an object gets garbage-collected. They are sometimes more 46adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * flexible than the {@link Object#finalize()} method. 47adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project */ 48adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Projectpublic class PhantomReference<T> extends Reference<T> { 49adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project 50adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project /** 51adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Constructs a new phantom reference and registers it with the given 52adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * reference queue. The reference queue may be {@code null}, but this case 53adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * does not make any sense, since the reference will never be enqueued, and 54adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * the {@link #get()} method always returns {@code null}. 55f33eae7e84eb6d3b0f4e86b59605bb3de73009f3Elliott Hughes * 56adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * @param r the referent to track 57adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * @param q the queue to register the phantom reference object with 58adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project */ 59adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project public PhantomReference(T r, ReferenceQueue<? super T> q) { 60ba1e5f9b7ffe3a42f1001ece077f566de8231548Carl Shapiro super(r, q); 61adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project } 62adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project 63adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project /** 64adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * Returns {@code null}. The referent of a phantom reference is not 65adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * accessible. 66f33eae7e84eb6d3b0f4e86b59605bb3de73009f3Elliott Hughes * 67adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project * @return {@code null} (always) 68adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project */ 69adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project @Override 70adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project public T get() { 71adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project return null; 72adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project } 73adc854b798c1cfe3bfd4c27d68d5cee38ca617daThe Android Open Source Project} 74