/*
* 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);
}
}