| 8 |
|
|
| 9 |
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/** |
| 10 |
|
* 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 |
|
* additional insertion, extraction, and inspection operations. |
| 13 |
|
* |
| 14 |
|
* <p>Queues typically, but do not necessarily, order elements in a |
| 16 |
|
* priority queues, which order elements according to a supplied |
| 17 |
|
* comparator, or the elements' natural ordering, and LIFO queues (or |
| 18 |
|
* stacks) which order the elements LIFO (last-in-first-out). |
| 19 |
< |
* Whatever the ordering used, the <em>head</em> of the queue is that element |
| 20 |
< |
* which would be removed by a call to {@link #remove() } or {@link #poll()}. |
| 21 |
< |
* Every Queue implementation must specify its ordering guarantees. |
| 22 |
< |
* |
| 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 |
| 26 |
< |
* failure. It is designed for use in collections in which failure to |
| 27 |
< |
* add is a normal, rather than exceptional occurrence, for example, |
| 28 |
< |
* in fixed-capacity (or "bounded") queues. |
| 29 |
< |
* |
| 19 |
> |
* Whatever the ordering used, the <em>head</em> of the queue is that |
| 20 |
> |
* element which would be removed by a call to {@link #remove() } or |
| 21 |
> |
* {@link #poll()}. In a FIFO queue, all new elements are inserted at |
| 22 |
> |
* the <em> tail</em> of the queue. Other kinds of queues may use |
| 23 |
> |
* different placement rules. Every <tt>Queue</tt> implementation |
| 24 |
> |
* must specify its ordering properties. |
| 25 |
> |
* |
| 26 |
> |
* <p>The {@link #offer offer} method inserts an element if possible, |
| 27 |
> |
* otherwise returning <tt>false</tt>. This differs from the {@link |
| 28 |
> |
* java.util.Collection#add Collection.add} method, which can fail to |
| 29 |
> |
* add an element only by throwing an unchecked exception. The |
| 30 |
> |
* <tt>offer</tt> method is designed for use when failure is a normal, |
| 31 |
> |
* rather than exceptional occurrence, for example, in fixed-capacity |
| 32 |
> |
* (or "bounded") queues. |
| 33 |
> |
* |
| 34 |
|
* <p>The {@link #remove()} and {@link #poll()} methods remove and |
| 35 |
|
* return the head of the queue. |
| 36 |
|
* Exactly which element is removed from the queue is a |
| 41 |
|
* while the <tt>poll()</tt> method returns <tt>null</tt>. |
| 42 |
|
* |
| 43 |
|
* <p>The {@link #element()} and {@link #peek()} methods return, but do |
| 44 |
< |
* not delete, the head of the queue. |
| 44 |
> |
* not remove, the head of the queue. |
| 45 |
|
* |
| 46 |
|
* <p>The <tt>Queue</tt> interface does not define the <i>blocking queue |
| 47 |
|
* methods</i>, which are common in concurrent programming. These methods, |
| 57 |
|
* used as a special return value by the <tt>poll</tt> method to |
| 58 |
|
* indicate that the queue contains no elements. |
| 59 |
|
* |
| 60 |
+ |
* <p><tt>Queue</tt> implementations generally do not define |
| 61 |
+ |
* element-based versions of methods <tt>equals</tt> and |
| 62 |
+ |
* <tt>hashCode</tt> but instead inherit the identity based versions |
| 63 |
+ |
* from class <tt>Object</tt>, because element-based equality is not |
| 64 |
+ |
* always well-defined for queues with the same elements but different |
| 65 |
+ |
* ordering properties. |
| 66 |
+ |
* |
| 67 |
+ |
* |
| 68 |
|
* <p>This interface is a member of the |
| 69 |
|
* <a href="{@docRoot}/../guide/collections/index.html"> |
| 70 |
|
* Java Collections Framework</a>. |
| 71 |
|
* |
| 72 |
< |
* @see Collection |
| 72 |
> |
* @see java.util.Collection |
| 73 |
|
* @see LinkedList |
| 74 |
|
* @see PriorityQueue |
| 75 |
< |
* @see java.util.concurrent.LinkedQueue |
| 75 |
> |
* @see java.util.concurrent.LinkedBlockingQueue |
| 76 |
|
* @see java.util.concurrent.BlockingQueue |
| 77 |
|
* @see java.util.concurrent.ArrayBlockingQueue |
| 78 |
|
* @see java.util.concurrent.LinkedBlockingQueue |
| 83 |
|
public interface Queue<E> extends Collection<E> { |
| 84 |
|
|
| 85 |
|
/** |
| 86 |
< |
* Add the specified element to this queue, if possible. |
| 86 |
> |
* Inserts the specified element to this queue, if possible. When |
| 87 |
> |
* using queues that may impose insertion restrictions (for |
| 88 |
> |
* example capacity bounds), method <tt>offer</tt> is generally |
| 89 |
> |
* preferable to method {@link Collection#add}, which can fail to |
| 90 |
> |
* insert an element only by throwing an exception. |
| 91 |
|
* |
| 92 |
< |
* @param element the element to add. |
| 93 |
< |
* @return <tt>true</tt> if it was possible to add the element to |
| 94 |
< |
* this queue. |
| 92 |
> |
* @param o the element to insert. |
| 93 |
> |
* @return <tt>true</tt> if it was possible to add the element to |
| 94 |
> |
* this queue, else <tt>false</tt> |
| 95 |
|
*/ |
| 96 |
< |
boolean offer(E element); |
| 96 |
> |
boolean offer(E o); |
| 97 |
|
|
| 98 |
|
/** |
| 99 |
< |
* Retrieve and remove the head of this queue, if it is available. |
| 99 |
> |
* Retrieves and removes the head of this queue, if it is available. |
| 100 |
|
* |
| 101 |
|
* @return the head of this queue, or <tt>null</tt> if this |
| 102 |
< |
* queue is empty. |
| 102 |
> |
* queue is empty. |
| 103 |
|
*/ |
| 104 |
|
E poll(); |
| 105 |
|
|
| 106 |
|
/** |
| 107 |
< |
* Retrieve and remove the head of this queue. |
| 107 |
> |
* Retrieves and removes the head of this queue. |
| 108 |
|
* This method differs |
| 109 |
< |
* from the <tt>poll</tt> method in that it throws an exception if the |
| 110 |
< |
* queue is empty. |
| 109 |
> |
* from the <tt>poll</tt> method in that it throws an exception if this |
| 110 |
> |
* queue is empty. |
| 111 |
|
* |
| 112 |
|
* @return the head of this queue. |
| 113 |
|
* @throws NoSuchElementException if this queue is empty. |
| 114 |
|
*/ |
| 115 |
< |
E remove() throws NoSuchElementException; |
| 115 |
> |
E remove(); |
| 116 |
|
|
| 117 |
|
/** |
| 118 |
< |
* Retrieve, but do not remove, the head of this queue, or <tt>null</tt> |
| 119 |
< |
* if this queue is empty. This method differs from the <tt>poll</tt> |
| 120 |
< |
* method only in that this method does not remove the element from |
| 118 |
> |
* Retrieves, but does not remove, the head of this queue. |
| 119 |
> |
* This method differs from the <tt>poll</tt> |
| 120 |
> |
* method only in that this method does not remove the head element from |
| 121 |
|
* this queue. |
| 122 |
|
* |
| 123 |
|
* @return the head of this queue, or <tt>null</tt> if this queue is empty. |
| 125 |
|
E peek(); |
| 126 |
|
|
| 127 |
|
/** |
| 128 |
< |
* Retrieve, but do not remove, the head of this queue. This method |
| 129 |
< |
* differs from the <tt>peek</tt> method only in that it throws an |
| 128 |
> |
* Retrieves, but does not remove, the head of this queue. This method |
| 129 |
> |
* differs from the <tt>peek</tt> method only in that it throws an |
| 130 |
|
* exception if this queue is empty. |
| 131 |
|
* |
| 132 |
|
* @return the head of this queue. |
| 133 |
|
* @throws NoSuchElementException if this queue is empty. |
| 134 |
|
*/ |
| 135 |
< |
E element() throws NoSuchElementException; |
| 135 |
> |
E element(); |
| 136 |
|
} |
| 121 |
– |
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| 122 |
– |
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| 123 |
– |
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| 124 |
– |
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| 125 |
– |
|
| 126 |
– |
|
| 127 |
– |
|
| 128 |
– |
|
| 129 |
– |
|
| 130 |
– |
|
