| 8 |
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|
| 9 |
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/** |
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* A collection designed for holding elements prior to processing. |
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< |
* Besides basic {@link java.util.Collection Collection} operations, |
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< |
* queues provide additional insertion, extraction, and inspection |
| 13 |
< |
* operations. Each of these methods exists in two forms: one throws |
| 14 |
< |
* an exception if the operation fails, the other returns a special |
| 15 |
< |
* value (either {@code null} or {@code false}, depending on the |
| 16 |
< |
* operation). The latter form of the insert operation is designed |
| 17 |
< |
* specifically for use with capacity-restricted {@code Queue} |
| 18 |
< |
* implementations; in most implementations, insert operations cannot |
| 19 |
< |
* fail. |
| 11 |
> |
* Besides basic {@link Collection} operations, queues provide |
| 12 |
> |
* additional insertion, extraction, and inspection operations. |
| 13 |
> |
* Each of these methods exists in two forms: one throws an exception |
| 14 |
> |
* if the operation fails, the other returns a special value (either |
| 15 |
> |
* {@code null} or {@code false}, depending on the operation). The |
| 16 |
> |
* latter form of the insert operation is designed specifically for |
| 17 |
> |
* use with capacity-restricted {@code Queue} implementations; in most |
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> |
* implementations, insert operations cannot fail. |
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* |
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< |
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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> |
* <table class="striped"> |
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|
* <caption>Summary of Queue methods</caption> |
| 22 |
+ |
* <thead> |
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|
* <tr> |
| 24 |
|
* <td></td> |
| 25 |
< |
* <td ALIGN=CENTER><em>Throws exception</em></td> |
| 26 |
< |
* <td ALIGN=CENTER><em>Returns special value</em></td> |
| 25 |
> |
* <th scope="col" style="font-weight:normal; font-style:italic">Throws exception</th> |
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> |
* <th scope="col" style="font-weight:normal; font-style:italic">Returns special value</th> |
| 27 |
|
* </tr> |
| 28 |
+ |
* </thead> |
| 29 |
+ |
* <tbody> |
| 30 |
|
* <tr> |
| 31 |
< |
* <td><b>Insert</b></td> |
| 32 |
< |
* <td>{@link Queue#add add(e)}</td> |
| 33 |
< |
* <td>{@link Queue#offer offer(e)}</td> |
| 31 |
> |
* <th scope="row">Insert</th> |
| 32 |
> |
* <td>{@link #add(Object) add(e)}</td> |
| 33 |
> |
* <td>{@link #offer(Object) offer(e)}</td> |
| 34 |
|
* </tr> |
| 35 |
|
* <tr> |
| 36 |
< |
* <td><b>Remove</b></td> |
| 37 |
< |
* <td>{@link Queue#remove remove()}</td> |
| 38 |
< |
* <td>{@link Queue#poll poll()}</td> |
| 36 |
> |
* <th scope="row">Remove</th> |
| 37 |
> |
* <td>{@link #remove() remove()}</td> |
| 38 |
> |
* <td>{@link #poll() poll()}</td> |
| 39 |
|
* </tr> |
| 40 |
|
* <tr> |
| 41 |
< |
* <td><b>Examine</b></td> |
| 42 |
< |
* <td>{@link Queue#element element()}</td> |
| 43 |
< |
* <td>{@link Queue#peek peek()}</td> |
| 41 |
> |
* <th scope="row">Examine</th> |
| 42 |
> |
* <td>{@link #element() element()}</td> |
| 43 |
> |
* <td>{@link #peek() peek()}</td> |
| 44 |
|
* </tr> |
| 45 |
+ |
* </tbody> |
| 46 |
|
* </table> |
| 47 |
|
* |
| 48 |
|
* <p>Queues typically, but do not necessarily, order elements in a |
| 51 |
|
* comparator, or the elements' natural ordering, and LIFO queues (or |
| 52 |
|
* stacks) which order the elements LIFO (last-in-first-out). |
| 53 |
|
* Whatever the ordering used, the <em>head</em> of the queue is that |
| 54 |
< |
* element which would be removed by a call to {@link #remove() } or |
| 54 |
> |
* element which would be removed by a call to {@link #remove()} or |
| 55 |
|
* {@link #poll()}. In a FIFO queue, all new elements are inserted at |
| 56 |
|
* the <em>tail</em> of the queue. Other kinds of queues may use |
| 57 |
|
* different placement rules. Every {@code Queue} implementation |
| 98 |
|
* always well-defined for queues with the same elements but different |
| 99 |
|
* ordering properties. |
| 100 |
|
* |
| 98 |
– |
* |
| 101 |
|
* <p>This interface is a member of the |
| 102 |
< |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 102 |
> |
* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> |
| 103 |
|
* Java Collections Framework</a>. |
| 104 |
|
* |
| 103 |
– |
* @see java.util.Collection |
| 104 |
– |
* @see LinkedList |
| 105 |
– |
* @see PriorityQueue |
| 106 |
– |
* @see java.util.concurrent.LinkedBlockingQueue |
| 107 |
– |
* @see java.util.concurrent.BlockingQueue |
| 108 |
– |
* @see java.util.concurrent.ArrayBlockingQueue |
| 109 |
– |
* @see java.util.concurrent.LinkedBlockingQueue |
| 110 |
– |
* @see java.util.concurrent.PriorityBlockingQueue |
| 105 |
|
* @since 1.5 |
| 106 |
|
* @author Doug Lea |
| 107 |
< |
* @param <E> the type of elements held in this collection |
| 107 |
> |
* @param <E> the type of elements held in this queue |
| 108 |
|
*/ |
| 109 |
|
public interface Queue<E> extends Collection<E> { |
| 110 |
|
/** |
| 147 |
|
|
| 148 |
|
/** |
| 149 |
|
* Retrieves and removes the head of this queue. This method differs |
| 150 |
< |
* from {@link #poll poll} only in that it throws an exception if this |
| 151 |
< |
* queue is empty. |
| 150 |
> |
* from {@link #poll() poll()} only in that it throws an exception if |
| 151 |
> |
* this queue is empty. |
| 152 |
|
* |
| 153 |
|
* @return the head of this queue |
| 154 |
|
* @throws NoSuchElementException if this queue is empty |
