[cvs] / jsr166 / src / main / java / util / Queue.java Repository:
ViewVC logotype

Diff of /jsr166/src/main/java/util/Queue.java

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 1.7, Tue Jun 24 14:34:30 2003 UTC revision 1.18, Sat Sep 13 18:51:06 2003 UTC
# Line 7  Line 7 
7  package java.util;  package java.util;
8    
9  /**  /**
10   * A Collection designed for holding elements prior to processing.   * A collection designed for holding elements prior to processing.
11   * Besides basic {@link Collection} operations, queues provide   * Besides basic {@link java.util.Collection Collection} operations, queues provide
12   * additional insertion, extraction, and inspection operations.   * additional insertion, extraction, and inspection operations.
13  0 *   *
14   * <p>Queues typically, but do not necessarily, order elements in a   * <p>Queues typically, but do not necessarily, order elements in a
15   * FIFO (first-in-first-out) manner.  Among the exceptions are   * FIFO (first-in-first-out) manner.  Among the exceptions are
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.  Every Queue   * comparator, or the elements' natural ordering, and LIFO queues (or
18   * implementation must specify its ordering guarantees.   * stacks) which order the elements LIFO (last-in-first-out).
19   *   * Whatever the ordering used, the <em>head</em> of the queue is that
20   * <p>The {@link #offer(E)} method adds an element if possible, otherwise   * element which would be removed by a call to {@link #remove() } or
21   * returning <tt>false</tt>.  This differs from the {@link   * {@link #poll()}.  In a FIFO queue, all new elements are inserted at
22   * Collections#add(Object)} method, which throws an unchecked exception upon   * the <em> tail</em> of the queue. Other kinds of queues may use
23   * failure. It is designed for use in collections in which failure to   * different placement rules.  Every <tt>Queue</tt> implementation
24   * add is a normal, rather than exceptional occurrence, for example,   * must specify its ordering properties.
25   * in fixed-capacity (or &ldquo;bounded&rdquo;) queues.   *
26     * <p>The {@link #offer offer} method inserts an element if possible,
27     * otherwise returning <tt>false</tt>.  This differs from the {@link
28     * 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 an element in accord with the implementation's ordering   * return the head of the queue.
36   * policy.  Exactly which element is removed from the queue is a   * Exactly which element is removed from the queue is a
37   * function of the queue's ordering policy, which differs from   * function of the queue's ordering policy, which differs from
38   * implementation to implementation.  Possible orderings include (but   * implementation to implementation. The <tt>remove()</tt> and
  * are not limited to) first-in-first-out (FIFO), last-in-first-out  
  * (LIFO), element priority, and arbitrary.  The <tt>remove()</tt> and  
39   * <tt>poll()</tt> methods differ only in their behavior when the   * <tt>poll()</tt> methods differ only in their behavior when the
40   * queue is empty: the <tt>remove()</tt> method throws an exception,   * queue is empty: the <tt>remove()</tt> method throws an exception,
41   * while the <tt>poll()</tt> method returns <tt>null</tt>.   * while the <tt>poll()</tt> method returns <tt>null</tt>.
42   *   *
43   * <p>The {@link #element()} and {@link #peek()} methods return but do   * <p>The {@link #element()} and {@link #peek()} methods return, but do
44   * not delete the element that would be obtained by a call to   * not remove, the head of the queue.
  * the <tt>remove</tt> and <tt>poll</tt> methods respectively.  
45   *   *
46   * <p>The <tt>Queue</tt> interface does not define the <i>blocking queue   * <p>The <tt>Queue</tt> interface does not define the <i>blocking queue
47   * methods</i>, which are common in concurrent programming.  These methods,   * methods</i>, which are common in concurrent programming.  These methods,
# Line 54  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>.
71   *   *
72   * @see 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 70  Line 81 
81   * @author Doug Lea   * @author Doug Lea
82   */   */
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 element the element to add.       * @param o the element to insert.
93       * @return true if it was possible to add the element to the queue.       * @return <tt>true</tt> if it was possible to add the element to
94         * this queue, else <tt>false</tt>
95       */       */
96      boolean offer(E element);      boolean offer(E o);
97    
98      /**      /**
99       * Remove and return an element from the queue if one is available.       * Retrieves and removes the head of this queue, or <tt>null</tt>
100         * if this queue is empty.
101       *       *
102       * @return an element previously on the queue, or <tt>null</tt> if the       * @return the head of this queue, or <tt>null</tt> if this
103       *         queue is empty.       *         queue is empty.
104       */       */
105      E poll();      E poll();
106    
107      /**      /**
108       * Remove and return an element from the queue.  This method differs       * Retrieves and removes the head of this queue.  This method
109       * from the <tt>poll</tt> method in that it throws an exception if the       * differs from the <tt>poll</tt> method in that it throws an
110       * queue is empty.       * exception if this queue is empty.
111       *       *
112       * @return an element previously on the queue.       * @return the head of this queue.
113       * @throws NoSuchElementException if the queue is empty.       * @throws NoSuchElementException if this queue is empty.
114       */       */
115      E remove() throws NoSuchElementException;      E remove();
116    
117      /**      /**
118       * Return, but do not remove, an element from the queue, or <tt>null</tt>       * Retrieves, but does not remove, the head of this queue,
119       * if the queue is empty.  This method returns the same object reference       * returning <tt>null</tt> if this queue is empty.
      * that would be returned by by the <tt>poll</tt> method.  The two methods  
      * differ in that this method does not remove the element from the queue.  
120       *       *
121       * @return an element on the queue, or <tt>null</tt> if the 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    
126      /**      /**
127       * Return, but do not remove, an element from the queue.  This method       * Retrieves, but does not remove, the head of this queue.  This method
128       * differs from the <tt>peek</tt> method in that it throws an exception if       * differs from the <tt>peek</tt> method only in that it throws an
129       * the queue is empty.       * exception if this queue is empty.
130       *       *
131       * @return an element on the queue.       * @return the head of this queue.
132       * @throws NoSuchElementException if the queue is empty.       * @throws NoSuchElementException if this queue is empty.
133       */       */
134      E element() throws NoSuchElementException;      E element();
135  }  }

Legend:
Removed from v.1.7  
changed lines
  Added in v.1.18

Doug Lea
ViewVC Help
Powered by ViewVC 1.0.8