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 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 collection.
     * The collection 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
     * collection, 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 collection.
     * @return <tt>true</tt> if this collection 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:	1.25
Committed:	Tue Jan 27 11:36:26 2004 UTC (20 years, 4 months ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PFD
Changes since 1.24:	+4 -0 lines
Log Message:	Add Collection framework membership doc
#	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			*
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			* throws an IllegalStateException.
51	dl	1.17	*
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	dholmes	1.11	* @throws NullPointerException if the specified element is <tt>null</tt>
57	dl	1.14	* @throws IllegalStateException if 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			/**
84			* Retrieves, but does not remove, the head of this queue.
85			* This implementation returns the result of <tt>peek</tt>
86			* unless the queue is empty.
87			*
88			* @return the head of this queue.
89			* @throws NoSuchElementException if this queue is empty.
90			*/
91	tim	1.8	public E element() {
92	tim	1.1	E x = peek();
93			if (x != null)
94			return x;
95			else
96			throw new NoSuchElementException();
97			}
98
99	dholmes	1.9	/**
100			* Removes all of the elements from this collection.
101			* The collection will be empty after this call returns.
102			* <p>This implementation repeatedly invokes {@link #poll poll} until it
103			* returns <tt>null</tt>.
104			*/
105	tim	1.1	public void clear() {
106			while (poll() != null)
107			;
108			}
109	dl	1.19
110			/**
111			* Adds all of the elements in the specified collection to this
112			* queue. Attempts to addAll of a queue to itself result in
113			* <tt>IllegalArgumentException</tt>. Further, the behavior of
114			* this operation is undefined if the specified collection is
115			* modified while the operation is in progress.
116			*
117			* <p>This implementation iterates over the specified collection,
118			* and adds each element returned by the iterator to this
119			* collection, in turn. A runtime exception encountered while
120			* trying to add an element (including, in particular, a
121			* <tt>null</tt> element) may result in only some of the elements
122			* having been successfully added when the associated exception is
123			* thrown.
124			*
125			* @param c collection whose elements are to be added to this collection.
126			* @return <tt>true</tt> if this collection changed as a result of the
127			* call.
128	dl	1.22	* @throws NullPointerException if the specified collection or
129	dl	1.19	* any of its elements are null.
130			* @throws IllegalArgumentException if c is this queue.
131			*
132			* @see #add(Object)
133			*/
134			public boolean addAll(Collection<? extends E> c) {
135			if (c == null)
136			throw new NullPointerException();
137			if (c == this)
138			throw new IllegalArgumentException();
139	jozart	1.23	boolean modified = false;
140			Iterator<? extends E> e = c.iterator();
141			while (e.hasNext()) {
142			if (add(e.next()))
143			modified = true;
144			}
145			return modified;
146	dl	1.19	}
147
148	dl	1.14	}