1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
|
/*
* Copyright (C) 2007 The Guava Authors
*
* 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 com.google.common.collect;
import com.google.common.annotations.GwtCompatible;
import java.util.NoSuchElementException;
import java.util.Queue;
/**
* A queue which forwards all its method calls to another queue. Subclasses
* should override one or more methods to modify the behavior of the backing
* queue as desired per the <a
* href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
*
* <p><b>Warning:</b> The methods of {@code ForwardingQueue} forward
* <b>indiscriminately</b> to the methods of the delegate. For example,
* overriding {@link #add} alone <b>will not</b> change the behavior of {@link
* #offer} which can lead to unexpected behavior. In this case, you should
* override {@code offer} as well, either providing your own implementation, or
* delegating to the provided {@code standardOffer} method.
*
* <p>The {@code standard} methods are not guaranteed to be thread-safe, even
* when all of the methods that they depend on are thread-safe.
*
* @author Mike Bostock
* @author Louis Wasserman
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible
public abstract class ForwardingQueue<E> extends ForwardingCollection<E>
implements Queue<E> {
/** Constructor for use by subclasses. */
protected ForwardingQueue() {}
@Override protected abstract Queue<E> delegate();
@Override
public boolean offer(E o) {
return delegate().offer(o);
}
@Override
public E poll() {
return delegate().poll();
}
@Override
public E remove() {
return delegate().remove();
}
@Override
public E peek() {
return delegate().peek();
}
@Override
public E element() {
return delegate().element();
}
/**
* A sensible definition of {@link #offer} in terms of {@link #add}. If you
* override {@link #add}, you may wish to override {@link #offer} to forward
* to this implementation.
*
* @since 7.0
*/
protected boolean standardOffer(E e) {
try {
return add(e);
} catch (IllegalStateException caught) {
return false;
}
}
/**
* A sensible definition of {@link #peek} in terms of {@link #element}. If you
* override {@link #element}, you may wish to override {@link #peek} to
* forward to this implementation.
*
* @since 7.0
*/
protected E standardPeek() {
try {
return element();
} catch (NoSuchElementException caught) {
return null;
}
}
/**
* A sensible definition of {@link #poll} in terms of {@link #remove}. If you
* override {@link #remove}, you may wish to override {@link #poll} to forward
* to this implementation.
*
* @since 7.0
*/
protected E standardPoll() {
try {
return remove();
} catch (NoSuchElementException caught) {
return null;
}
}
}
|
