8 |
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|
9 |
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/** |
10 |
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* A collection designed for holding elements prior to processing. |
11 |
< |
* Besides basic {@link Collection} operations, queues provide |
11 |
> |
* Besides basic {@link java.util.Collection Collection} operations, queues provide |
12 |
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* additional insertion, extraction, and inspection operations. |
13 |
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* |
14 |
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* <p>Queues typically, but do not necessarily, order elements in a |
18 |
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* stacks) which order the elements LIFO (last-in-first-out). |
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* Whatever the ordering used, the <em>head</em> of the queue is that element |
20 |
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* which would be removed by a call to {@link #remove() } or {@link #poll()}. |
21 |
< |
* Every Queue implementation must specify its ordering guarantees. |
21 |
> |
* Every <tt>Queue</tt> implementation must specify its ordering guarantees. |
22 |
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* |
23 |
< |
* <p>The {@link #offer(E)} method adds an element if possible, otherwise |
24 |
< |
* returning <tt>false</tt>. This differs from the {@link |
25 |
< |
* Collections#add(Object)} method, which throws an unchecked exception upon |
23 |
> |
* <p>The {@link #offer offer} method adds an element if possible, otherwise |
24 |
> |
* returning <tt>false</tt>. This differs from the |
25 |
> |
* {@link java.util.Collection#add Collection.add} |
26 |
> |
* method, which throws an unchecked exception upon |
27 |
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* failure. It is designed for use in collections in which failure to |
28 |
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* add is a normal, rather than exceptional occurrence, for example, |
29 |
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* in fixed-capacity (or "bounded") queues. |
30 |
< |
* |
30 |
> |
* |
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* <p>The {@link #remove()} and {@link #poll()} methods remove and |
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* return the head of the queue. |
33 |
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* Exactly which element is removed from the queue is a |
38 |
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* while the <tt>poll()</tt> method returns <tt>null</tt>. |
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* |
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* <p>The {@link #element()} and {@link #peek()} methods return, but do |
41 |
< |
* not delete, the head of the queue. |
41 |
> |
* not remove, the head of the queue. |
42 |
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* |
43 |
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* <p>The <tt>Queue</tt> interface does not define the <i>blocking queue |
44 |
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* methods</i>, which are common in concurrent programming. These methods, |
54 |
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* used as a special return value by the <tt>poll</tt> method to |
55 |
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* indicate that the queue contains no elements. |
56 |
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* |
57 |
+ |
* <p><tt>Queue</tt> implementations generally do not define |
58 |
+ |
* element-based versions of methods <tt>equals</tt> and |
59 |
+ |
* <tt>hashCode</tt> but instead inherit the identity based versions |
60 |
+ |
* from class <tt>Object</tt>, because element-based equality is not |
61 |
+ |
* always well-defined for queues with the same elements but different |
62 |
+ |
* ordering properties. |
63 |
+ |
* |
64 |
+ |
* |
65 |
|
* <p>This interface is a member of the |
66 |
|
* <a href="{@docRoot}/../guide/collections/index.html"> |
67 |
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* Java Collections Framework</a>. |
68 |
|
* |
69 |
< |
* @see Collection |
69 |
> |
* @see java.util.Collection |
70 |
|
* @see LinkedList |
71 |
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* @see PriorityQueue |
72 |
< |
* @see java.util.concurrent.LinkedQueue |
72 |
> |
* @see java.util.concurrent.LinkedBlockingQueue |
73 |
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* @see java.util.concurrent.BlockingQueue |
74 |
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* @see java.util.concurrent.ArrayBlockingQueue |
75 |
|
* @see java.util.concurrent.LinkedBlockingQueue |
80 |
|
public interface Queue<E> extends Collection<E> { |
81 |
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|
82 |
|
/** |
83 |
< |
* Add the specified element to this queue, if possible. |
83 |
> |
* Adds the specified element to this queue, if possible. |
84 |
|
* |
85 |
< |
* @param element the element to add. |
86 |
< |
* @return <tt>true</tt> if it was possible to add the element to |
87 |
< |
* this queue. |
85 |
> |
* @param o the element to add. |
86 |
> |
* @return <tt>true</tt> if it was possible to add the element to |
87 |
> |
* this queue, else <tt>false</tt> |
88 |
|
*/ |
89 |
< |
boolean offer(E element); |
89 |
> |
boolean offer(E o); |
90 |
|
|
91 |
|
/** |
92 |
< |
* Retrieve and remove the head of this queue, if it is available. |
92 |
> |
* Retrieves and removes the head of this queue, if it is available. |
93 |
|
* |
94 |
|
* @return the head of this queue, or <tt>null</tt> if this |
95 |
< |
* queue is empty. |
95 |
> |
* queue is empty. |
96 |
|
*/ |
97 |
|
E poll(); |
98 |
|
|
99 |
|
/** |
100 |
< |
* Retrieve and remove the head of this queue. |
100 |
> |
* Retrieves and removes the head of this queue. |
101 |
|
* This method differs |
102 |
< |
* from the <tt>poll</tt> method in that it throws an exception if the |
103 |
< |
* queue is empty. |
102 |
> |
* from the <tt>poll</tt> method in that it throws an exception if this |
103 |
> |
* queue is empty. |
104 |
|
* |
105 |
|
* @return the head of this queue. |
106 |
|
* @throws NoSuchElementException if this queue is empty. |
107 |
|
*/ |
108 |
< |
E remove() throws NoSuchElementException; |
108 |
> |
E remove(); |
109 |
|
|
110 |
|
/** |
111 |
< |
* Retrieve, but do not remove, the head of this queue, or <tt>null</tt> |
112 |
< |
* if this queue is empty. This method differs from the <tt>poll</tt> |
113 |
< |
* method only in that this method does not remove the element from |
111 |
> |
* Retrieves, but does not remove, the head of this queue. |
112 |
> |
* This method differs from the <tt>poll</tt> |
113 |
> |
* method only in that this method does not remove the head element from |
114 |
|
* this queue. |
115 |
|
* |
116 |
|
* @return the head of this queue, or <tt>null</tt> if this queue is empty. |
118 |
|
E peek(); |
119 |
|
|
120 |
|
/** |
121 |
< |
* Retrieve, but do not remove, the head of this queue. This method |
122 |
< |
* differs from the <tt>peek</tt> method only in that it throws an |
121 |
> |
* Retrieves, but does not remove, the head of this queue. This method |
122 |
> |
* differs from the <tt>peek</tt> method only in that it throws an |
123 |
|
* exception if this queue is empty. |
124 |
|
* |
125 |
|
* @return the head of this queue. |
126 |
|
* @throws NoSuchElementException if this queue is empty. |
127 |
|
*/ |
128 |
< |
E element() throws NoSuchElementException; |
128 |
> |
E element(); |
129 |
|
} |
130 |
|
|
131 |
|
|