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 per the spec for {@link Collection#add})
     * @throws IllegalStateException if the element cannot be added at this
     *         time due to capacity restrictions
     * @throws NullPointerException if the specified element is null and
     *         this queue not permit null elements
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @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} 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} 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 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 contains a
     *         null element and this queue does not permit null elements,
     *         or if the specified collection is null
     * @throws ClassCastException if the class of an element of the specified
     *         collection prevents it from being added to this queue
     * @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:	1.28
Committed:	Sat May 14 01:55:29 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.27:	+45 -26 lines
Log Message:	doc fixes
#	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	* 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	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
57	* @throws IllegalStateException if the element cannot be added at this
58	* time due to capacity restrictions
59	* @throws NullPointerException if the specified element is null and
60	* this queue not permit null elements
61	* @throws ClassCastException if the class of the specified element
62	* prevents it from being added to this queue
63	* @throws IllegalArgumentException if some property of this element
64	* prevents it from being added to this queue
65	*/
66	public boolean add(E e) {
67	if (offer(e))
68	return true;
69	else
70	throw new IllegalStateException("Queue full");
71	}
72
73	/**
74	* Retrieves and removes the head of this queue. This method differs
75	* from {@link #poll} only in that it throws an exception if this queue
76	* is empty.
77	*
78	* <p>This implementation returns the result of <tt>poll</tt>
79	* unless the queue is empty.
80	*
81	* @return the head of this queue
82	* @throws NoSuchElementException if this queue is empty
83	*/
84	public E remove() {
85	E x = poll();
86	if (x != null)
87	return x;
88	else
89	throw new NoSuchElementException();
90	}
91
92	/**
93	* Retrieves, but does not remove, the head of this queue. This method
94	* differs from {@link #peek} only in that it throws an exception if
95	* this queue is empty.
96	*
97	* <p>This implementation returns the result of <tt>peek</tt>
98	* unless the queue is empty.
99	*
100	* @return the head of this queue
101	* @throws NoSuchElementException if this queue is empty
102	*/
103	public E element() {
104	E x = peek();
105	if (x != null)
106	return x;
107	else
108	throw new NoSuchElementException();
109	}
110
111	/**
112	* Removes all of the elements from this queue.
113	* The queue will be empty after this call returns.
114	*
115	* <p>This implementation repeatedly invokes {@link #poll poll} until it
116	* returns <tt>null</tt>.
117	*/
118	public void clear() {
119	while (poll() != null)
120	;
121	}
122
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	* queue, in turn. A runtime exception encountered while
133	* 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	* @param c collection whose elements are to be added to this queue
139	* @return <tt>true</tt> if this queue changed as a result of the call
140	* @throws NullPointerException if the specified collection contains a
141	* null element and this queue does not permit null elements,
142	* or if the specified collection is null
143	* @throws ClassCastException if the class of an element of the specified
144	* collection prevents it from being added to this queue
145	* @throws IllegalArgumentException if some property of an element of the
146	* specified collection prevents it from being added to this
147	* queue, or if the specified collection is this queue
148	* @throws IllegalStateException if not all the elements can be added at
149	* this time due to insertion restrictions
150	* @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	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	}
165
166	}