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 o 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 o) {
        if (offer(o))
            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:	1.26
Committed:	Tue Apr 26 19:54:03 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.25:	+13 -14 lines
Log Message:	doc fixes
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	dl	1.24	* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/licenses/publicdomain
5	dl	1.2	*/
6
7	tim	1.1	package java.util;
8
9			/**
10	dl	1.14	* 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	dholmes	1.9	* <tt>null</tt> returns.
18	dl	1.14	*
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	dl	1.16	* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
23			* {@link Collection#iterator} supporting {@link
24	dl	1.18	* Iterator#remove}. Typically, additional methods will be overridden
25	dl	1.16	* as well. If these requirements cannot be met, consider instead
26			* subclassing {@link AbstractCollection}.
27	dl	1.14	*
28	dl	1.25	* <p>This class is a member of the
29			* <a href="{@docRoot}/../guide/collections/index.html">
30			* Java Collections Framework</a>.
31	jsr166	1.26	*
32	dl	1.4	* @since 1.5
33			* @author Doug Lea
34	dl	1.21	* @param <E> the type of elements held in this collection
35	tim	1.1	*/
36	tim	1.10	public abstract class AbstractQueue<E>
37			extends AbstractCollection<E>
38	dholmes	1.9	implements Queue<E> {
39	tim	1.5
40	dl	1.14	/**
41			* Constructor for use by subclasses.
42			*/
43			protected AbstractQueue() {
44			}
45	tim	1.1
46	dholmes	1.12
47			/**
48	dl	1.14	* Adds the specified element to this queue. This implementation
49			* returns <tt>true</tt> if <tt>offer</tt> succeeds, else
50	jsr166	1.26	* throws an IllegalStateException.
51			*
52	dl	1.14	* @param o the element
53	tim	1.10	* @return <tt>true</tt> (as per the general contract of
54	dl	1.14	* <tt>Collection.add</tt>).
55	dholmes	1.9	*
56	jsr166	1.26	* @throws NullPointerException if the specified element is <tt>null</tt>.
57			* @throws IllegalStateException if the element cannot be added.
58	dholmes	1.9	*/
59			public boolean add(E o) {
60			if (offer(o))
61	tim	1.1	return true;
62			else
63			throw new IllegalStateException("Queue full");
64			}
65
66	dholmes	1.9	/**
67	dl	1.14	* 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	dholmes	1.9	*
71	dl	1.14	* @return the head of this queue.
72			* @throws NoSuchElementException if this queue is empty.
73	dholmes	1.9	*/
74	tim	1.8	public E remove() {
75	tim	1.1	E x = poll();
76			if (x != null)
77			return x;
78			else
79			throw new NoSuchElementException();
80			}
81
82	dl	1.14	/**
83	jsr166	1.26	* Retrieves, but does not remove, the head of this queue.
84	dl	1.14	* 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	tim	1.8	public E element() {
91	tim	1.1	E x = peek();
92			if (x != null)
93			return x;
94			else
95			throw new NoSuchElementException();
96			}
97
98	dholmes	1.9	/**
99	jsr166	1.26	* Removes all of the elements from this queue.
100			* The queue will be empty after this call returns.
101	dholmes	1.9	* <p>This implementation repeatedly invokes {@link #poll poll} until it
102			* returns <tt>null</tt>.
103			*/
104	tim	1.1	public void clear() {
105			while (poll() != null)
106			;
107			}
108	dl	1.19
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	jsr166	1.26	* queue, in turn. A runtime exception encountered while
119	dl	1.19	* 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	jsr166	1.26	* @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	dl	1.19	* call.
127	dl	1.22	* @throws NullPointerException if the specified collection or
128	jsr166	1.26	* any of its elements are null.
129	dl	1.19	* @throws IllegalArgumentException if c is this queue.
130	jsr166	1.26	*
131	dl	1.19	* @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	jozart	1.23	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	dl	1.19	}
146
147	dl	1.14	}