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revision 1.11, Thu Jul 31 19:49:42 2003 UTC revision 1.17, Fri Sep 12 15:38:26 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(E)} method adds an element if possible, otherwise   * different placement rules.  Every <tt>Queue</tt> implementation
24   * returning <tt>false</tt>.  This differs from the {@link java.util.Collection#add Collection.add(E)}   * must specify its ordering properties.
25   * method, which throws an unchecked exception upon   *
26   * failure. It is designed for use in collections in which failure to   * <p>The {@link #offer offer} method inserts an element if possible,
27   * add is a normal, rather than exceptional occurrence, for example,   * otherwise returning <tt>false</tt>.  This differs from the {@link
28   * in fixed-capacity (or &quot;bounded&quot;) queues.   * java.util.Collection#add Collection.add} method, which can fail to
29     * 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 53  Line 57 
57   * used as a special return value by the <tt>poll</tt> method to   * used as a special return value by the <tt>poll</tt> method to
58   * indicate that the queue contains no elements.   * indicate that the queue contains no elements.
59   *   *
60     * <p><tt>Queue</tt> implementations generally do not define
61     * element-based versions of methods <tt>equals</tt> and
62     * <tt>hashCode</tt> but instead inherit the identity based versions
63     * from class <tt>Object</tt>, because element-based equality is not
64     * always well-defined for queues with the same elements but different
65     * ordering properties.
66     *
67     *
68   * <p>This interface is a member of the   * <p>This interface is a member of the
69   * <a href="{@docRoot}/../guide/collections/index.html">   * <a href="{@docRoot}/../guide/collections/index.html">
70   * Java Collections Framework</a>.   * Java Collections Framework</a>.
# Line 60  Line 72 
72   * @see java.util.Collection   * @see java.util.Collection
73   * @see LinkedList   * @see LinkedList
74   * @see PriorityQueue   * @see PriorityQueue
75   * @see java.util.concurrent.LinkedQueue   * @see java.util.concurrent.LinkedBlockingQueue
76   * @see java.util.concurrent.BlockingQueue   * @see java.util.concurrent.BlockingQueue
77   * @see java.util.concurrent.ArrayBlockingQueue   * @see java.util.concurrent.ArrayBlockingQueue
78   * @see java.util.concurrent.LinkedBlockingQueue   * @see java.util.concurrent.LinkedBlockingQueue
# Line 71  Line 83 
83  public interface Queue<E> extends Collection<E> {  public interface Queue<E> extends Collection<E> {
84    
85      /**      /**
86       * Add the specified element to this queue, if possible.       * Inserts the specified element to 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       * Retrieve and remove the head of this queue, if it is available.       * Retrieves and removes the head of this queue, if it is available.
100       *       *
101       * @return the head of this queue, or <tt>null</tt> if this       * @return the head of this queue, or <tt>null</tt> if this
102       *         queue is empty.       *         queue is empty.
# Line 88  Line 104 
104      E poll();      E poll();
105    
106      /**      /**
107       * Retrieve and remove the head of this queue.       * Retrieves and removes the head of this queue.
108       * This method differs       * This method differs
109       * from the <tt>poll</tt> method in that it throws an exception if this       * from the <tt>poll</tt> method in that it throws an exception if this
110       * queue is empty.       * queue is empty.
# Line 99  Line 115 
115      E remove();      E remove();
116    
117      /**      /**
118       * Retrieve, but do 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>       * This method differs from the <tt>poll</tt>
120       * method only in that this method does not remove the head element from       * method only in that this method does not remove the head element from
121       * this queue.       * this queue.
# Line 109  Line 125 
125      E peek();      E peek();
126    
127      /**      /**
128       * Retrieve, but do not remove, the head of this queue.  This method       * Retrieves, but does not remove, the head of this queue.  This method
129       * differs from the <tt>peek</tt> method only in that it throws an       * differs from the <tt>peek</tt> method only in that it throws an
130       * exception if this queue is empty.       * exception if this queue is empty.
131       *       *
# Line 118  Line 134 
134       */       */
135      E element();      E element();
136  }  }
   
   
   
   
   
   
   
   
   
   

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