java/util/AbstractQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package java.util;

/**
 * This class provides skeletal implementations of some {@link Queue}
 * operations. The implementations in this class are appropriate when
 * the base implementation does <em>not</em> allow <tt>null</tt>
 * elements.  Methods {@link #add add}, {@link #remove remove}, and
 * {@link #element element} are based on {@link #offer offer}, {@link
 * #poll poll}, and {@link #peek peek}, respectively but throw
 * exceptions instead of indicating failure via <tt>false</tt> or
 * <tt>null</tt> returns.
 *
 * <p> A <tt>Queue</tt> implementation that extends this class must
 * minimally define a method {@link Queue#offer} which does not permit
 * insertion of <tt>null</tt> elements, along with methods {@link
 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
 * {@link Collection#iterator} supporting {@link
 * Iterator#remove}. Typically, additional methods will be overridden
 * as well. If these requirements cannot be met, consider instead
 * subclassing {@link AbstractCollection}.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public abstract class AbstractQueue<E>
    extends AbstractCollection<E>
    implements Queue<E> {

    /**
     * Constructor for use by subclasses.
     */
    protected AbstractQueue() {
    }


    /**
     * Adds the specified element to this queue. This implementation
     * returns <tt>true</tt> if <tt>offer</tt> succeeds, else
     * throws an IllegalStateException.
     *
     * @param e the element
     * @return <tt>true</tt> (as per the general contract of
     *         <tt>Collection.add</tt>).
     *
     * @throws NullPointerException if the specified element is <tt>null</tt>.
     * @throws IllegalStateException if the element cannot be added.
     */
    public boolean add(E e) {
        if (offer(e))
            return true;
        else
            throw new IllegalStateException("Queue full");
    }

    /**
     * Retrieves and removes the head of this queue.
     * This implementation returns the result of <tt>poll</tt>
     * unless the queue is empty.
     *
     * @return the head of this queue.
     * @throws NoSuchElementException if this queue is empty.
     */
    public E remove() {
        E x = poll();
        if (x != null)
            return x;
        else
            throw new NoSuchElementException();
    }

    /**
     * Retrieves, but does not remove, the head of this queue.
     * This implementation returns the result of <tt>peek</tt>
     * unless the queue is empty.
     *
     * @return the head of this queue.
     * @throws NoSuchElementException if this queue is empty.
     */
    public E element() {
        E x = peek();
        if (x != null)
            return x;
        else
            throw new NoSuchElementException();
    }

    /**
     * Removes all of the elements from this queue.
     * The queue will be empty after this call returns.
     * <p>This implementation repeatedly invokes {@link #poll poll} until it
     * returns <tt>null</tt>.
     */
    public void clear() {
        while (poll() != null)
            ;
    }

    /**
     * Adds all of the elements in the specified collection to this
     * queue.  Attempts to addAll of a queue to itself result in
     * <tt>IllegalArgumentException</tt>. Further, the behavior of
     * this operation is undefined if the specified collection is
     * modified while the operation is in progress.
     *
     * <p>This implementation iterates over the specified collection,
     * and adds each element returned by the iterator to this
     * queue, in turn.  A runtime exception encountered while
     * trying to add an element (including, in particular, a
     * <tt>null</tt> element) may result in only some of the elements
     * having been successfully added when the associated exception is
     * thrown.
     *
     * @param c collection whose elements are to be added to this queue.
     * @return <tt>true</tt> if this queue changed as a result of the
     *         call.
     * @throws NullPointerException if the specified collection or
     *         any of its elements are null.
     * @throws IllegalArgumentException if c is this queue.
     *
     * @see #add(Object)
     */
    public boolean addAll(Collection<? extends E> c) {
        if (c == null)
            throw new NullPointerException();
        if (c == this)
            throw new IllegalArgumentException();
        boolean modified = false;
        Iterator<? extends E> e = c.iterator();
        while (e.hasNext()) {
            if (add(e.next()))
                modified = true;
        }
        return modified;
    }

}
Revision:	1.27
Committed:	Mon May 2 08:35:49 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.26:	+3 -3 lines
Log Message:	E o -> E e
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
5	*/
6
7	package java.util;
8
9	/**
10	* This class provides skeletal implementations of some {@link Queue}
11	* operations. The implementations in this class are appropriate when
12	* the base implementation does <em>not</em> allow <tt>null</tt>
13	* elements. Methods {@link #add add}, {@link #remove remove}, and
14	* {@link #element element} are based on {@link #offer offer}, {@link
15	* #poll poll}, and {@link #peek peek}, respectively but throw
16	* exceptions instead of indicating failure via <tt>false</tt> or
17	* <tt>null</tt> returns.
18	*
19	* <p> A <tt>Queue</tt> implementation that extends this class must
20	* minimally define a method {@link Queue#offer} which does not permit
21	* insertion of <tt>null</tt> elements, along with methods {@link
22	* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
23	* {@link Collection#iterator} supporting {@link
24	* Iterator#remove}. Typically, additional methods will be overridden
25	* as well. If these requirements cannot be met, consider instead
26	* subclassing {@link AbstractCollection}.
27	*
28	* <p>This class is a member of the
29	* <a href="{@docRoot}/../guide/collections/index.html">
30	* Java Collections Framework</a>.
31	*
32	* @since 1.5
33	* @author Doug Lea
34	* @param <E> the type of elements held in this collection
35	*/
36	public abstract class AbstractQueue<E>
37	extends AbstractCollection<E>
38	implements Queue<E> {
39
40	/**
41	* Constructor for use by subclasses.
42	*/
43	protected AbstractQueue() {
44	}
45
46
47	/**
48	* Adds the specified element to this queue. This implementation
49	* returns <tt>true</tt> if <tt>offer</tt> succeeds, else
50	* throws an IllegalStateException.
51	*
52	* @param e the element
53	* @return <tt>true</tt> (as per the general contract of
54	* <tt>Collection.add</tt>).
55	*
56	* @throws NullPointerException if the specified element is <tt>null</tt>.
57	* @throws IllegalStateException if the element cannot be added.
58	*/
59	public boolean add(E e) {
60	if (offer(e))
61	return true;
62	else
63	throw new IllegalStateException("Queue full");
64	}
65
66	/**
67	* Retrieves and removes the head of this queue.
68	* This implementation returns the result of <tt>poll</tt>
69	* unless the queue is empty.
70	*
71	* @return the head of this queue.
72	* @throws NoSuchElementException if this queue is empty.
73	*/
74	public E remove() {
75	E x = poll();
76	if (x != null)
77	return x;
78	else
79	throw new NoSuchElementException();
80	}
81
82	/**
83	* Retrieves, but does not remove, the head of this queue.
84	* This implementation returns the result of <tt>peek</tt>
85	* unless the queue is empty.
86	*
87	* @return the head of this queue.
88	* @throws NoSuchElementException if this queue is empty.
89	*/
90	public E element() {
91	E x = peek();
92	if (x != null)
93	return x;
94	else
95	throw new NoSuchElementException();
96	}
97
98	/**
99	* Removes all of the elements from this queue.
100	* The queue will be empty after this call returns.
101	* <p>This implementation repeatedly invokes {@link #poll poll} until it
102	* returns <tt>null</tt>.
103	*/
104	public void clear() {
105	while (poll() != null)
106	;
107	}
108
109	/**
110	* Adds all of the elements in the specified collection to this
111	* queue. Attempts to addAll of a queue to itself result in
112	* <tt>IllegalArgumentException</tt>. Further, the behavior of
113	* this operation is undefined if the specified collection is
114	* modified while the operation is in progress.
115	*
116	* <p>This implementation iterates over the specified collection,
117	* and adds each element returned by the iterator to this
118	* queue, in turn. A runtime exception encountered while
119	* trying to add an element (including, in particular, a
120	* <tt>null</tt> element) may result in only some of the elements
121	* having been successfully added when the associated exception is
122	* thrown.
123	*
124	* @param c collection whose elements are to be added to this queue.
125	* @return <tt>true</tt> if this queue changed as a result of the
126	* call.
127	* @throws NullPointerException if the specified collection or
128	* any of its elements are null.
129	* @throws IllegalArgumentException if c is this queue.
130	*
131	* @see #add(Object)
132	*/
133	public boolean addAll(Collection<? extends E> c) {
134	if (c == null)
135	throw new NullPointerException();
136	if (c == this)
137	throw new IllegalArgumentException();
138	boolean modified = false;
139	Iterator<? extends E> e = c.iterator();
140	while (e.hasNext()) {
141	if (add(e.next()))
142	modified = true;
143	}
144	return modified;
145	}
146
147	}