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/*
 * 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
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/*
 * 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
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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:
 *
 * 
    *
  • * A set {@code ref} of references is determined. {@code ref} contains the * following elements: *
      *
    • * All weak references pointing to {@code obj}. *
    • *
    • * All weak references pointing to objects from which {@code obj} is * either strongly or softly reachable. *
    • *
    *
  • *
  • * All references in {@code ref} are atomically cleared. *
  • *
  • * All objects formerly being referenced by {@code ref} become eligible for * finalization. *
  • *
  • * At some future point, all references in {@code ref} will be enqueued * with their corresponding reference queues, if any. *
  • *
* * 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: * *
    *
  • * A {@code SoftReference} should be cleared and enqueued as late as * possible, that is, in case the VM is in danger of running out of * memory. *
  • *
  • * A {@code WeakReference} may be cleared and enqueued as soon as is * known to be weakly-referenced. *
  • *
*/ public class WeakReference extends Reference { /** * 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 q) { super(r, q); } }




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