1   /*
2    * Copyright (C) 2007 The Guava Authors
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package com.google.common.base;
18  
19  import java.lang.ref.PhantomReference;
20  import java.lang.ref.ReferenceQueue;
21  
22  /**
23   * Phantom reference with a {@code finalizeReferent()} method which a background thread invokes
24   * after the garbage collector reclaims the referent. This is a simpler alternative to using a
25   * {@link ReferenceQueue}.
26   *
27   * <p>Unlike a normal phantom reference, this reference will be cleared automatically.
28   *
29   * @author Bob Lee
30   * @since 2.0 (imported from Google Collections Library)
31   */
32  public abstract class FinalizablePhantomReference<T> extends PhantomReference<T>
33      implements FinalizableReference {
34    /**
35     * Constructs a new finalizable phantom reference.
36     *
37     * @param referent to phantom reference
38     * @param queue that should finalize the referent
39     */
40    protected FinalizablePhantomReference(T referent, FinalizableReferenceQueue queue) {
41      super(referent, queue.queue);
42      queue.cleanUp();
43    }
44  }