| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| /* |
| * Copyright (C) 2008 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package java.lang.ref; |
| |
| /** |
| * Implements a weak reference, which is the middle of the three types of |
| * references. Once the garbage collector decides that an object {@code obj} is |
| * is weakly-reachable, the following |
| * happens: |
| * |
| * <ul> |
| * <li> |
| * A set {@code ref} of references is determined. {@code ref} contains the |
| * following elements: |
| * <ul> |
| * <li> |
| * All weak references pointing to {@code obj}. |
| * </li> |
| * <li> |
| * All weak references pointing to objects from which {@code obj} is |
| * either strongly or softly reachable. |
| * </li> |
| * </ul> |
| * </li> |
| * <li> |
| * All references in {@code ref} are atomically cleared. |
| * </li> |
| * <li> |
| * All objects formerly being referenced by {@code ref} become eligible for |
| * finalization. |
| * </li> |
| * <li> |
| * At some future point, all references in {@code ref} will be enqueued |
| * with their corresponding reference queues, if any. |
| * </li> |
| * </ul> |
| * |
| * Weak references are useful for mappings that should have their entries |
| * removed automatically once they are not referenced any more (from outside). |
| * The difference between a {@code SoftReference} and a {@code WeakReference} is |
| * the point of time at which the decision is made to clear and enqueue the |
| * reference: |
| * |
| * <ul> |
| * <li> |
| * A {@code SoftReference} should be cleared and enqueued <em>as late as |
| * possible</em>, that is, in case the VM is in danger of running out of |
| * memory. |
| * </li> |
| * <li> |
| * A {@code WeakReference} may be cleared and enqueued as soon as is |
| * known to be weakly-referenced. |
| * </li> |
| * </ul> |
| */ |
| public class WeakReference<T> extends Reference<T> { |
| |
| /** |
| * Constructs a new weak reference to the given referent. The newly created |
| * reference is not registered with any reference queue. |
| * |
| * @param r the referent to track |
| */ |
| public WeakReference(T r) { |
| super(r, null); |
| } |
| |
| /** |
| * Constructs a new weak reference to the given referent. The newly created |
| * reference is registered with the given reference queue. |
| * |
| * @param r the referent to track |
| * @param q the queue to register to the reference object with. A null value |
| * results in a weak reference that is not associated with any |
| * queue. |
| */ |
| public WeakReference(T r, ReferenceQueue<? super T> q) { |
| super(r, q); |
| } |
| } |