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() {
    }

    /**
     * Inserts the specified element into this queue if it is possible to do so
     * immediately without violating capacity restrictions, returning
     * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
     * if no space is currently available.
     *
     * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
     * else throws an <tt>IllegalStateException</tt>.
     *
     * @param e the element to add
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     * @throws IllegalStateException if the element cannot be added at this
     *         time due to capacity restrictions
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null and
     *         this queue not permit null elements
     * @throws IllegalArgumentException if some property of this element
     *         prevents it from being added to this queue
     */
    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 method differs
     * from {@link #poll poll} only in that it throws an exception if this
     * queue is empty.
     *
     * <p>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 method
     * differs from {@link #peek peek} only in that it throws an exception if
     * this queue is empty.
     *
     * <p>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 containing elements to be added to this queue
     * @return <tt>true</tt> if this queue changed as a result of the call
     * @throws ClassCastException if the class of an element of the specified
     *         collection prevents it from being added to this queue
     * @throws NullPointerException if the specified collection contains a
     *         null element and this queue does not permit null elements,
     *         or if the specified collection is null
     * @throws IllegalArgumentException if some property of an element of the
     *         specified collection prevents it from being added to this
     *         queue, or if the specified collection is this queue
     * @throws IllegalStateException if not all the elements can be added at
     *         this time due to insertion restrictions
     * @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:	1.32
Committed:	Tue Feb 7 20:54:24 2006 UTC (18 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.31:	+0 -1 lines
Log Message:	6378729: Remove workaround for 6280605
#	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	jsr166	1.28	* Inserts the specified element into this queue if it is possible to do so
48			* immediately without violating capacity restrictions, returning
49			* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
50			* if no space is currently available.
51			*
52			* <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
53			* else throws an <tt>IllegalStateException</tt>.
54			*
55			* @param e the element to add
56	jsr166	1.31	* @return <tt>true</tt> (as specified by {@link Collection#add})
57	jsr166	1.28	* @throws IllegalStateException if the element cannot be added at this
58			* time due to capacity restrictions
59	jsr166	1.29	* @throws ClassCastException if the class of the specified element
60			* prevents it from being added to this queue
61	jsr166	1.28	* @throws NullPointerException if the specified element is null and
62			* this queue not permit null elements
63			* @throws IllegalArgumentException if some property of this element
64			* prevents it from being added to this queue
65	dholmes	1.9	*/
66	jsr166	1.27	public boolean add(E e) {
67			if (offer(e))
68	tim	1.1	return true;
69			else
70			throw new IllegalStateException("Queue full");
71			}
72
73	dholmes	1.9	/**
74	jsr166	1.28	* Retrieves and removes the head of this queue. This method differs
75	jsr166	1.31	* from {@link #poll poll} only in that it throws an exception if this
76			* queue is empty.
77	jsr166	1.28	*
78			* <p>This implementation returns the result of <tt>poll</tt>
79	dl	1.14	* unless the queue is empty.
80	dholmes	1.9	*
81	jsr166	1.28	* @return the head of this queue
82			* @throws NoSuchElementException if this queue is empty
83	dholmes	1.9	*/
84	tim	1.8	public E remove() {
85	tim	1.1	E x = poll();
86			if (x != null)
87			return x;
88			else
89			throw new NoSuchElementException();
90			}
91
92	dl	1.14	/**
93	jsr166	1.28	* Retrieves, but does not remove, the head of this queue. This method
94	jsr166	1.31	* differs from {@link #peek peek} only in that it throws an exception if
95	jsr166	1.28	* this queue is empty.
96			*
97			* <p>This implementation returns the result of <tt>peek</tt>
98	dl	1.14	* unless the queue is empty.
99			*
100	jsr166	1.28	* @return the head of this queue
101			* @throws NoSuchElementException if this queue is empty
102	dl	1.14	*/
103	tim	1.8	public E element() {
104	tim	1.1	E x = peek();
105			if (x != null)
106			return x;
107			else
108			throw new NoSuchElementException();
109			}
110
111	dholmes	1.9	/**
112	jsr166	1.26	* Removes all of the elements from this queue.
113			* The queue will be empty after this call returns.
114	jsr166	1.28	*
115	dholmes	1.9	* <p>This implementation repeatedly invokes {@link #poll poll} until it
116			* returns <tt>null</tt>.
117			*/
118	tim	1.1	public void clear() {
119			while (poll() != null)
120			;
121			}
122	dl	1.19
123			/**
124			* Adds all of the elements in the specified collection to this
125			* queue. Attempts to addAll of a queue to itself result in
126			* <tt>IllegalArgumentException</tt>. Further, the behavior of
127			* this operation is undefined if the specified collection is
128			* modified while the operation is in progress.
129			*
130			* <p>This implementation iterates over the specified collection,
131			* and adds each element returned by the iterator to this
132	jsr166	1.26	* queue, in turn. A runtime exception encountered while
133	dl	1.19	* trying to add an element (including, in particular, a
134			* <tt>null</tt> element) may result in only some of the elements
135			* having been successfully added when the associated exception is
136			* thrown.
137			*
138	jsr166	1.30	* @param c collection containing elements to be added to this queue
139	jsr166	1.28	* @return <tt>true</tt> if this queue changed as a result of the call
140	jsr166	1.29	* @throws ClassCastException if the class of an element of the specified
141			* collection prevents it from being added to this queue
142	jsr166	1.28	* @throws NullPointerException if the specified collection contains a
143			* null element and this queue does not permit null elements,
144			* or if the specified collection is null
145			* @throws IllegalArgumentException if some property of an element of the
146	jsr166	1.29	* specified collection prevents it from being added to this
147			* queue, or if the specified collection is this queue
148	jsr166	1.28	* @throws IllegalStateException if not all the elements can be added at
149			* this time due to insertion restrictions
150	dl	1.19	* @see #add(Object)
151			*/
152			public boolean addAll(Collection<? extends E> c) {
153			if (c == null)
154			throw new NullPointerException();
155			if (c == this)
156			throw new IllegalArgumentException();
157	jozart	1.23	boolean modified = false;
158			Iterator<? extends E> e = c.iterator();
159			while (e.hasNext()) {
160			if (add(e.next()))
161			modified = true;
162			}
163			return modified;
164	dl	1.19	}
165
166	dl	1.14	}