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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. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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* Expert Group and released to the public domain, as explained at |
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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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* <tt>AbstractQueue</tt> provides default implementations of |
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* {@link #add add}, {@link #remove remove}, and {@link #element element} |
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* based on |
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* {@link #offer offer}, {@link #poll poll}, and {@link #peek peek}, |
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* respectively but that |
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* throw exceptions instead of indicating failure via <tt>false</tt> or |
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* <tt>null</tt> returns. |
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* <p>The provided implementations all assume that the base implementation |
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* does <em>not</em> allow <tt>null</tt> elements. |
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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 {@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 {@code false} or |
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* {@code null} returns. |
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* |
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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 {@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}/../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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*/ |
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public abstract class AbstractQueue<E> |
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extends AbstractCollection<E> |
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implements Queue<E> { |
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// note that optional methods are not optional here or in our subclasses, |
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// so we redefine each optional method to document that it is not optional |
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// We also inherit, or define, all necessary @throws comments |
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// /** |
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// * @throws NullPointerException if the specified element is <tt>null</tt> |
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// */ |
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// public abstract boolean offer(E o); |
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/** |
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* Constructor for use by subclasses. |
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*/ |
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protected AbstractQueue() { |
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} |
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/** |
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* Adds the specified element to this queue. |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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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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* {@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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* @throws NullPointerException if the specified element is <tt>null</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 {@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 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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public boolean add(E o) { |
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if (offer(o)) |
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public boolean add(E e) { |
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if (offer(e)) |
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return true; |
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else |
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throw new IllegalStateException("Queue full"); |
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} |
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/** |
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* Adds all of the elements in the specified collection to this queue. |
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* The behavior of this operation is undefined if |
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* the specified collection is modified while the operation is in |
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* progress. (This implies that the behavior of this call is undefined if |
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* the specified collection is this queue, and this queue is nonempty.) |
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* <p> |
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* This implementation iterates over the specified collection, and adds |
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* each object returned by the iterator to this queue, in turn. |
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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 collection changed as a result of the |
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* call. |
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* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt> |
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* is <tt>null</tt> |
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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 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 {@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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* @throws NoSuchElementException if this queue is empty |
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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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return super.addAll(c); |
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} |
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/** @throws NoSuchElementException {@inheritDoc} */ |
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public E remove() { |
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E x = poll(); |
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if (x != null) |
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throw new NoSuchElementException(); |
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} |
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/** @throws NoSuchElementException {@inheritDoc} */ |
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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 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 {@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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* @throws NoSuchElementException if this queue is empty |
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*/ |
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public E element() { |
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E x = peek(); |
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if (x != null) |
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} |
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/** |
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* Removes all of the elements from this collection. |
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* The collection will be empty after this call returns. |
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* Removes all of the elements from 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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} |
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// XXX Remove this redundant declaration, pending response from Neal Gafter. |
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public abstract Iterator<E> iterator(); |
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} |
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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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* {@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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* <p>This implementation iterates over the specified collection, |
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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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* {@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 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 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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* @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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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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if (c == null) |
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throw new NullPointerException(); |
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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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for (E e : c) |
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if (add(e)) |
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modified = true; |
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return modified; |
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} |
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} |
