ViewVC Help
View File | Revision Log | Show Annotations | Download File | Root Listing
root/jsr166/jsr166/src/main/java/util/Queue.java
(Generate patch)

Comparing jsr166/src/main/java/util/Queue.java (file contents):
Revision 1.4 by dl, Sat Jun 7 18:31:00 2003 UTC vs.
Revision 1.16 by dl, Sat Aug 30 11:40:04 2003 UTC

# Line 7 | Line 7
7   package java.util;
8  
9   /**
10 < * A Collection designed for holding elements prior to processing.
11 < * Besides basic {@link Collection} operations, queues provide
10 > * A collection designed for holding elements prior to processing.
11 > * Besides basic {@link java.util.Collection Collection} operations, queues provide
12   * additional insertion, extraction, and inspection operations.
13   *
14   * <p>Queues typically, but do not necessarily, order elements in a
15 < * FIFO (first-in-first-out) manner.  Among the exceptions are priority
16 < * queues, which order elements according to a supplied comparators, or
17 < * the elements natural ordering.  Every Queue implementation must specify
18 < * its ordering guarantees.
19 < *
20 < * <p>The {@link #offer(E)} method adds an element if possible, otherwise
21 < * returning <tt>false</tt>.  This differs from the {@link
22 < * Collections#add(Object)} method, which throws an unchecked exception upon
15 > * FIFO (first-in-first-out) manner.  Among the exceptions are
16 > * priority queues, which order elements according to a supplied
17 > * comparator, or the elements' natural ordering, and LIFO queues (or
18 > * 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
20 > * which would be removed by a call to {@link #remove() } or {@link #poll()}.
21 > * Every <tt>Queue</tt> implementation must specify its ordering guarantees.
22 > *
23 > * <p>The {@link #offer offer} method adds an element if possible, otherwise
24 > * returning <tt>false</tt>.  This differs from the
25 > * {@link java.util.Collection#add Collection.add}
26 > * method, which throws an unchecked exception upon
27   * failure. It is designed for use in collections in which failure to
28   * add is a normal, rather than exceptional occurrence, for example,
29 < * in fixed-capacity (or &ldquo;bounded&rdquo;) queues.
30 <
31 < *
32 < * <p>The {@link #remove()} and {@link #poll()} methods remove and return an
33 < * element in accord with the implementation's ordering policy.
34 < * Exactly which element is removed from the queue is a function
35 < * of the queue's ordering policy, which differs from implementation
36 < * to implementation.  Possible orderings include (but are not limited
37 < * to) first-in-first-out (FIFO), element priority, and arbitrary.
38 < * The <tt>remove()</tt> and <tt>poll()</tt> methods differ only in their
39 < * behavior when the queue is empty: the <tt>remove()</tt> method throws an
40 < * exception, while the <tt>poll()</tt> method returns <tt>null</tt>.
41 < *
38 < * <p>The {@link #element()} and {@link #peek()} methods return but do
39 < * not delete the element that would be obtained by a call to
40 < * the <tt>remove</tt> and <tt>poll</tt> methods respectively.
29 > * in fixed-capacity (or &quot;bounded&quot;) queues.
30 > *
31 > * <p>The {@link #remove()} and {@link #poll()} methods remove and
32 > * return the head of the queue.
33 > * Exactly which element is removed from the queue is a
34 > * function of the queue's ordering policy, which differs from
35 > * implementation to implementation. The <tt>remove()</tt> and
36 > * <tt>poll()</tt> methods differ only in their behavior when the
37 > * queue is empty: the <tt>remove()</tt> method throws an exception,
38 > * while the <tt>poll()</tt> method returns <tt>null</tt>.
39 > *
40 > * <p>The {@link #element()} and {@link #peek()} methods return, but do
41 > * not remove, the head of the queue.
42   *
43   * <p>The <tt>Queue</tt> interface does not define the <i>blocking queue
44   * methods</i>, which are common in concurrent programming.  These methods,
# Line 45 | Line 46 | package java.util;
46   * defined in the {@link java.util.concurrent.BlockingQueue} interface, which
47   * extends this interface.
48   *
49 < * <p><tt>Queue</tt> implementations generally do not allow insertion of
50 < * <tt>null</tt> elements.  Even in the few implementations that permit it,
51 < * it is a bad idea, as <tt>null</tt> is also used as a special return value
52 < * by the <tt>poll</tt> method to indicate that the queue contains no
53 < * elements.
49 > * <p><tt>Queue</tt> implementations generally do not allow insertion
50 > * of <tt>null</tt> elements, although some implementations, such as
51 > * {@link LinkedList}, do not prohibit insertion of <tt>null</tt>.
52 > * Even in the implementations that permit it, <tt>null</tt> should
53 > * not be inserted into a <tt>Queue</tt>, as <tt>null</tt> is also
54 > * used as a special return value by the <tt>poll</tt> method to
55 > * indicate that the queue contains no elements.
56 > *
57 > * <p><tt>Queue</tt> implementations generally do not define
58 > * element-based versions of methods <tt>equals</tt> and
59 > * <tt>hashCode</tt> but instead inherit the identity based versions
60 > * from class <tt>Object</tt>, because element-based equality is not
61 > * always well-defined for queues with the same elements but different
62 > * ordering properties.
63 > *
64   *
65   * <p>This interface is a member of the
66   * <a href="{@docRoot}/../guide/collections/index.html">
67   * Java Collections Framework</a>.
68   *
69 < * @see Collection
69 > * @see java.util.Collection
70   * @see LinkedList
71   * @see PriorityQueue
72 < * @see LinkedQueue
72 > * @see java.util.concurrent.LinkedBlockingQueue
73   * @see java.util.concurrent.BlockingQueue
74   * @see java.util.concurrent.ArrayBlockingQueue
75   * @see java.util.concurrent.LinkedBlockingQueue
76   * @see java.util.concurrent.PriorityBlockingQueue
77 + * @since 1.5
78 + * @author Doug Lea
79   */
80   public interface Queue<E> extends Collection<E> {
81 +
82      /**
83 <     * Add the specified element to this queue, if possible.
83 >     * Adds the specified element to this queue, if possible.
84       *
85 <     * @param element the element to add.
86 <     * @return true if it was possible to add the element to the queue.
85 >     * @param o the element to add.
86 >     * @return <tt>true</tt> if it was possible to add the element to
87 >     * this queue, else <tt>false</tt>
88       */
89 <    public boolean offer(E element);
89 >    boolean offer(E o);
90  
91      /**
92 <     * Remove and return an element from the queue if one is available.
92 >     * Retrieves and removes the head of this queue, if it is available.
93       *
94 <     * @return an element previously on the queue, or <tt>null</tt> if the
95 <     *         queue is empty.
94 >     * @return the head of this queue, or <tt>null</tt> if this
95 >     *         queue is empty.
96       */
97 <    public E poll();
97 >    E poll();
98  
99      /**
100 <     * Remove and return an element from the queue.  This method differs
101 <     * from the <tt>poll</tt> method in that it throws an exception if the
102 <     * queue is empty.
100 >     * Retrieves and removes the head of this queue.
101 >     * This method differs
102 >     * from the <tt>poll</tt> method in that it throws an exception if this
103 >     * queue is empty.
104       *
105 <     * @return an element previously on the queue.
106 <     * @throws NoSuchElementException if the queue is empty.
105 >     * @return the head of this queue.
106 >     * @throws NoSuchElementException if this queue is empty.
107       */
108 <    public E remove() throws NoSuchElementException;
108 >    E remove();
109  
110      /**
111 <     * Return, but do not remove, an element from the queue, or <tt>null</tt>
112 <     * if the queue is empty.  This method returns the same object reference
113 <     * that would be returned by by the <tt>poll</tt> method.  The two methods
114 <     * differ in that this method does not remove the element from the queue.
111 >     * Retrieves, but does not remove, the head of this queue.
112 >     * This method differs from the <tt>poll</tt>
113 >     * method only in that this method does not remove the head element from
114 >     * this queue.
115       *
116 <     * @return an element on the queue, or <tt>null</tt> if the queue is empty.
116 >     * @return the head of this queue, or <tt>null</tt> if this queue is empty.
117       */
118 <    public E peek();
118 >    E peek();
119  
120      /**
121 <     * Return, but do not remove, an element from the queue.  This method
122 <     * differs from the <tt>peek</tt> method in that it throws an exception if
123 <     * the queue is empty.
121 >     * Retrieves, but does not remove, the head of this queue.  This method
122 >     * differs from the <tt>peek</tt> method only in that it throws an
123 >     * exception if this queue is empty.
124       *
125 <     * @return an element on the queue.
126 <     * @throws NoSuchElementException if the queue is empty.
125 >     * @return the head of this queue.
126 >     * @throws NoSuchElementException if this queue is empty.
127       */
128 <    public E element() throws NoSuchElementException;
128 >    E element();
129   }
130 +
131 +
132 +
133 +
134 +
135 +
136 +
137 +
138 +
139 +

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines