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revision 1.16, Sat Aug 30 11:40:04 2003 UTC revision 1.19, Mon Sep 15 12:02:23 2003 UTC
# Line 16  Line 16 
16   * priority queues, which order elements according to a supplied   * priority queues, which order elements according to a supplied
17   * comparator, or the elements' natural ordering, and LIFO queues (or   * comparator, or the elements' natural ordering, and LIFO queues (or
18   * stacks) which order the elements LIFO (last-in-first-out).   * 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   * Whatever the ordering used, the <em>head</em> of the queue is that
20   * which would be removed by a call to {@link #remove() } or {@link #poll()}.   * element which would be removed by a call to {@link #remove() } or
21   * Every <tt>Queue</tt> implementation must specify its ordering guarantees.   * {@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   * <p>The {@link #offer offer} method adds an element if possible, otherwise   * different placement rules.  Every <tt>Queue</tt> implementation
24   * returning <tt>false</tt>.  This differs from the   * must specify its ordering properties.
25   * {@link java.util.Collection#add Collection.add}   *
26   * method, which throws an unchecked exception upon   * <p>The {@link #offer offer} method inserts an element if possible,
27   * failure. It is designed for use in collections in which failure to   * otherwise returning <tt>false</tt>.  This differs from the {@link
28   * add is a normal, rather than exceptional occurrence, for example,   * java.util.Collection#add Collection.add} method, which can fail to
29   * in fixed-capacity (or &quot;bounded&quot;) queues.   * 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 &quot;bounded&quot;) queues.
33   *   *
34   * <p>The {@link #remove()} and {@link #poll()} methods remove and   * <p>The {@link #remove()} and {@link #poll()} methods remove and
35   * return the head of the queue.   * return the head of the queue.
# Line 80  Line 83 
83  public interface Queue<E> extends Collection<E> {  public interface Queue<E> extends Collection<E> {
84    
85      /**      /**
86       * Adds the specified element to this queue, if possible.       * Inserts the specified element into 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 o the element to add.       * @param o the element to insert.
93       * @return <tt>true</tt> if it was possible to add the element to       * @return <tt>true</tt> if it was possible to add the element to
94       * this queue, else <tt>false</tt>       * this queue, else <tt>false</tt>
95       */       */
96      boolean offer(E o);      boolean offer(E o);
97    
98      /**      /**
99       * Retrieves and removes the head of this queue, if it is available.       * Retrieves and removes the head of this queue, or <tt>null</tt>
100         * if this queue is empty.
101       *       *
102       * @return the head of this queue, or <tt>null</tt> if this       * @return the head of this queue, or <tt>null</tt> if this
103       *         queue is empty.       *         queue is empty.
# Line 97  Line 105 
105      E poll();      E poll();
106    
107      /**      /**
108       * Retrieves and removes the head of this queue.       * Retrieves and removes the head of this queue.  This method
109       * This method differs       * differs from the <tt>poll</tt> method in that it throws an
110       * from the <tt>poll</tt> method in that it throws an exception if this       * exception if this queue is empty.
      * queue is empty.  
111       *       *
112       * @return the head of this queue.       * @return the head of this queue.
113       * @throws NoSuchElementException if this queue is empty.       * @throws NoSuchElementException if this queue is empty.
# Line 108  Line 115 
115      E remove();      E remove();
116    
117      /**      /**
118       * Retrieves, but does not remove, the head of this queue.       * Retrieves, but does not remove, the head of this queue,
119       * This method differs from the <tt>poll</tt>       * returning <tt>null</tt> if this queue is empty.
      * method only in that this method does not remove the head element from  
      * this queue.  
120       *       *
121       * @return the head of this queue, or <tt>null</tt> if this queue is empty.       * @return the head of this queue, or <tt>null</tt> if this queue
122         * is empty.
123       */       */
124      E peek();      E peek();
125    
# Line 127  Line 133 
133       */       */
134      E element();      E element();
135  }  }
   
   
   
   
   
   
   
   
   
   

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