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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/licenses/publicdomain |
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*/ |
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package java.util; |
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* <p> A <tt>Queue</tt> 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}, {@link |
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* Collection#remove}, and a {@link Collection#iterator} supporting |
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* {@link Iterator#remove}. If these requirements cannot be met, |
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* consider instead subclassing {@link AbstractCollection}. |
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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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* |
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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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* 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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protected AbstractQueue() { |
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} |
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|
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/** |
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* Inserts the specified element to this queue, if possible. |
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* |
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* @param o the element to add. |
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* @return <tt>true</tt> if it was possible to add the element to |
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* this queue, else <tt>false</tt> |
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* @throws NullPointerException if the specified element is <tt>null</tt> |
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*/ |
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public boolean offer(E o) { return false; } |
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// FIXME: Replace above no-op with following abstract version |
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// when javac allows it. |
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// public abstract boolean offer(E o); |
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/** |
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* Adds the specified element to this queue. This implementation |
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* returns <tt>true</tt> if <tt>offer</tt> succeeds, else |
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* throws an IllegalStateException. |
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* th |
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* @param o the element |
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* throws an IllegalStateException. |
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* |
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* @param e the element |
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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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* |
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* @throws NullPointerException if the specified element is <tt>null</tt> |
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* @throws IllegalStateException if element cannot be added |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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* @throws IllegalStateException if the element cannot be added. |
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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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throw new NoSuchElementException(); |
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} |
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/** |
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* Retrieves, but does not remove, the head of this queue. |
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* Retrieves, but does not remove, the head of this queue. |
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* This implementation returns the result of <tt>peek</tt> |
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* unless the queue is empty. |
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* |
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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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* <p>This implementation repeatedly invokes {@link #poll poll} until it |
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* returns <tt>null</tt>. |
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*/ |
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; |
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} |
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// Declarations that mostly just remove optionality clauses. |
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/** |
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* Removes a single instance of the specified element from this |
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* queue, if one is present. More formally, removes an element |
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* <tt>e</tt> such that <tt>(o==null ? e==null : |
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* o.equals(e))</tt>, if the queue contains such an element. |
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* Returns <tt>true</tt> if the queue contained the specified |
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* element (or equivalently, if the queue changed as a result of |
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* the call). |
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* |
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* @param o the element to remove |
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* @return true if the element was removed |
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*/ |
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public abstract boolean remove(Object o); |
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|
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/** |
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* Removes from this queue all of its elements that are contained in |
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* the specified collection. <p> |
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* |
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* This implementation iterates over this queue, checking each |
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* element returned by the iterator in turn to see if it's contained |
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* in the specified collection. If it's so contained, it's removed from |
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* this queue with the iterator's <tt>remove</tt> method.<p> |
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* |
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* @param c elements to be removed from this collection. |
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* @return <tt>true</tt> if this queue changed as a result of the |
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* call. |
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* @throws NullPointerException if the specified collection is null. |
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*/ |
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public boolean removeAll(Collection<?> c) { |
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return super.removeAll(c); |
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} |
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|
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/** |
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* Retains only the elements in this queue that are contained in the |
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* specified collection. In other words, removes |
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* from this queue all of its elements that are not contained in the |
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* specified collection. <p> |
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* |
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* This implementation iterates over this queue, checking each |
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* element returned by the iterator in turn to see if it's contained |
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* in the specified collection. If it's not so contained, it's removed |
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* from this queue with the iterator's <tt>remove</tt> method.<p> |
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* |
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* @param c elements to be retained in this collection. |
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* @return <tt>true</tt> if this queue changed as a result of the |
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* call. |
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* @throws NullPointerException if the specified collection is null. |
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* |
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*/ |
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public boolean retainAll(Collection<?> c) { |
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return super.retainAll(c); |
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} |
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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. The behavior of this operation is undefined if the |
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* specified collection is modified while the operation is in |
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* progress. (This implies that the behavior of this call is |
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* undefined if the specified collection is this queue, and this |
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* queue is nonempty.) |
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* |
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* <p> This implementation iterates over the specified collection, |
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* and uses the <tt>add</tt> method to insert each object returned by |
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* the iterator to this queue, in turn. |
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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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* 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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* <tt>null</tt> 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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* @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 |
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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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* @throws IllegalStateException if any element cannot be added. |
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* |
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* @throws NullPointerException if the specified collection or |
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* any of its elements are null. |
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* @throws IllegalArgumentException if c is this queue. |
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* |
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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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return super.addAll(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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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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modified = true; |
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} |
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return modified; |
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} |
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} |
