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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package java.util; |
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/** |
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* This class provides skeletal implementations of some {@link Queue} |
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* operations. The implementations in this class are appropriate when |
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* the base implementation does <em>not</em> allow <tt>null</tt> |
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* the base implementation does <em>not</em> allow {@code null} |
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* elements. Methods {@link #add add}, {@link #remove remove}, and |
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* {@link #element element} are based on {@link #offer offer}, {@link |
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* #poll poll}, and {@link #peek peek}, respectively but throw |
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* exceptions instead of indicating failure via <tt>false</tt> or |
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* <tt>null</tt> returns. |
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* #poll poll}, and {@link #peek peek}, respectively, but throw |
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* exceptions instead of indicating failure via {@code false} or |
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* {@code null} returns. |
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* |
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* <p> A <tt>Queue</tt> implementation that extends this class must |
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* <p>A {@code Queue} implementation that extends this class must |
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* minimally define a method {@link Queue#offer} which does not permit |
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* insertion of <tt>null</tt> elements, along with methods {@link |
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* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a |
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* {@link Collection#iterator} supporting {@link |
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* Iterator#remove}. Typically, additional methods will be overridden |
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* as well. If these requirements cannot be met, consider instead |
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* subclassing {@link AbstractCollection}. |
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* insertion of {@code null} elements, along with methods {@link |
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* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and |
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* {@link Collection#iterator}. Typically, additional methods will be |
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* overridden as well. If these requirements cannot be met, consider |
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* instead subclassing {@link AbstractCollection}. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <E> the type of elements held in this collection |
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* @param <E> the type of elements held in this queue |
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*/ |
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public abstract class AbstractQueue<E> |
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extends AbstractCollection<E> |
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/** |
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* Inserts the specified element into this queue if it is possible to do so |
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* immediately without violating capacity restrictions, returning |
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* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> |
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* {@code true} upon success and throwing an {@code IllegalStateException} |
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* if no space is currently available. |
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* |
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* <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds, |
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* else throws an <tt>IllegalStateException</tt>. |
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* <p>This implementation returns {@code true} if {@code offer} succeeds, |
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* else throws an {@code IllegalStateException}. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
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* @return {@code true} (as specified by {@link Collection#add}) |
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* @throws IllegalStateException if the element cannot be added at this |
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* time due to capacity restrictions |
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* @throws NullPointerException if the specified element is null and |
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* this queue not permit null elements |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this queue |
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* @throws NullPointerException if the specified element is null and |
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* this queue does not permit null elements |
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* @throws IllegalArgumentException if some property of this element |
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* prevents it from being added to this queue |
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*/ |
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/** |
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* Retrieves and removes the head of this queue. This method differs |
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* from {@link #poll} only in that it throws an exception if this queue |
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* is empty. |
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* from {@link #poll poll} only in that it throws an exception if this |
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* queue is empty. |
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* |
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* <p>This implementation returns the result of <tt>poll</tt> |
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* <p>This implementation returns the result of {@code poll} |
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* unless the queue is empty. |
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* |
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* @return the head of this queue |
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|
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/** |
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* Retrieves, but does not remove, the head of this queue. This method |
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* differs from {@link #peek} only in that it throws an exception if |
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* differs from {@link #peek peek} only in that it throws an exception if |
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* this queue is empty. |
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* |
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* <p>This implementation returns the result of <tt>peek</tt> |
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* <p>This implementation returns the result of {@code peek} |
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* unless the queue is empty. |
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* |
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* @return the head of this queue |
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* The queue will be empty after this call returns. |
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* |
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* <p>This implementation repeatedly invokes {@link #poll poll} until it |
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* returns <tt>null</tt>. |
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* returns {@code null}. |
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*/ |
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public void clear() { |
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while (poll() != null) |
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/** |
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* Adds all of the elements in the specified collection to this |
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* queue. Attempts to addAll of a queue to itself result in |
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* <tt>IllegalArgumentException</tt>. Further, the behavior of |
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* {@code IllegalArgumentException}. Further, the behavior of |
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* this operation is undefined if the specified collection is |
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* modified while the operation is in progress. |
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* |
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* and adds each element returned by the iterator to this |
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* queue, in turn. A runtime exception encountered while |
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* trying to add an element (including, in particular, a |
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* <tt>null</tt> element) may result in only some of the elements |
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* {@code null} element) may result in only some of the elements |
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* having been successfully added when the associated exception is |
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* thrown. |
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* |
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* @param c collection whose elements are to be added to this queue |
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* @return <tt>true</tt> if this queue changed as a result of the call |
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* @param c collection containing elements to be added to this queue |
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* @return {@code true} if this queue changed as a result of the call |
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* @throws ClassCastException if the class of an element of the specified |
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* collection prevents it from being added to this queue |
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* @throws NullPointerException if the specified collection contains a |
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* null element and this queue does not permit null elements, |
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* or if the specified collection is null |
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* @throws ClassCastException if the class of an element of the specified |
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* collection prevents it from being added to this queue |
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* @throws IllegalArgumentException if some property of an element of the |
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* specified collection prevents it from being added to this |
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* queue, or if the specified collection is this queue |
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* specified collection prevents it from being added to this |
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* queue, or if the specified collection is this queue |
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* @throws IllegalStateException if not all the elements can be added at |
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* this time due to insertion restrictions |
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* @see #add(Object) |
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if (c == this) |
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throw new IllegalArgumentException(); |
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boolean modified = false; |
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Iterator<? extends E> e = c.iterator(); |
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while (e.hasNext()) { |
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if (add(e.next())) |
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for (E e : c) |
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if (add(e)) |
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modified = true; |
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} |
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return modified; |
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} |
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