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;
import java.util.*; // for javadoc (till 6280605 is fixed)

/**
 * 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:	1.31
Committed:	Mon Jul 18 19:14:17 2005 UTC (18 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.30:	+5 -4 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	import java.util.*; // for javadoc (till 6280605 is fixed)
9
10	/**
11	* This class provides skeletal implementations of some {@link Queue}
12	* operations. The implementations in this class are appropriate when
13	* the base implementation does <em>not</em> allow <tt>null</tt>
14	* elements. Methods {@link #add add}, {@link #remove remove}, and
15	* {@link #element element} are based on {@link #offer offer}, {@link
16	* #poll poll}, and {@link #peek peek}, respectively but throw
17	* exceptions instead of indicating failure via <tt>false</tt> or
18	* <tt>null</tt> returns.
19	*
20	* <p> A <tt>Queue</tt> implementation that extends this class must
21	* minimally define a method {@link Queue#offer} which does not permit
22	* insertion of <tt>null</tt> elements, along with methods {@link
23	* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
24	* {@link Collection#iterator} supporting {@link
25	* Iterator#remove}. Typically, additional methods will be overridden
26	* as well. If these requirements cannot be met, consider instead
27	* subclassing {@link AbstractCollection}.
28	*
29	* <p>This class is a member of the
30	* <a href="{@docRoot}/../guide/collections/index.html">
31	* Java Collections Framework</a>.
32	*
33	* @since 1.5
34	* @author Doug Lea
35	* @param <E> the type of elements held in this collection
36	*/
37	public abstract class AbstractQueue<E>
38	extends AbstractCollection<E>
39	implements Queue<E> {
40
41	/**
42	* Constructor for use by subclasses.
43	*/
44	protected AbstractQueue() {
45	}
46
47	/**
48	* Inserts the specified element into this queue if it is possible to do so
49	* immediately without violating capacity restrictions, returning
50	* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
51	* if no space is currently available.
52	*
53	* <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
54	* else throws an <tt>IllegalStateException</tt>.
55	*
56	* @param e the element to add
57	* @return <tt>true</tt> (as specified by {@link Collection#add})
58	* @throws IllegalStateException if the element cannot be added at this
59	* time due to capacity restrictions
60	* @throws ClassCastException if the class of the specified element
61	* prevents it from being added to this queue
62	* @throws NullPointerException if the specified element is null and
63	* this queue not permit null elements
64	* @throws IllegalArgumentException if some property of this element
65	* prevents it from being added to this queue
66	*/
67	public boolean add(E e) {
68	if (offer(e))
69	return true;
70	else
71	throw new IllegalStateException("Queue full");
72	}
73
74	/**
75	* Retrieves and removes the head of this queue. This method differs
76	* from {@link #poll poll} only in that it throws an exception if this
77	* queue is empty.
78	*
79	* <p>This implementation returns the result of <tt>poll</tt>
80	* unless the queue is empty.
81	*
82	* @return the head of this queue
83	* @throws NoSuchElementException if this queue is empty
84	*/
85	public E remove() {
86	E x = poll();
87	if (x != null)
88	return x;
89	else
90	throw new NoSuchElementException();
91	}
92
93	/**
94	* Retrieves, but does not remove, the head of this queue. This method
95	* differs from {@link #peek peek} only in that it throws an exception if
96	* this queue is empty.
97	*
98	* <p>This implementation returns the result of <tt>peek</tt>
99	* unless the queue is empty.
100	*
101	* @return the head of this queue
102	* @throws NoSuchElementException if this queue is empty
103	*/
104	public E element() {
105	E x = peek();
106	if (x != null)
107	return x;
108	else
109	throw new NoSuchElementException();
110	}
111
112	/**
113	* Removes all of the elements from this queue.
114	* The queue will be empty after this call returns.
115	*
116	* <p>This implementation repeatedly invokes {@link #poll poll} until it
117	* returns <tt>null</tt>.
118	*/
119	public void clear() {
120	while (poll() != null)
121	;
122	}
123
124	/**
125	* Adds all of the elements in the specified collection to this
126	* queue. Attempts to addAll of a queue to itself result in
127	* <tt>IllegalArgumentException</tt>. Further, the behavior of
128	* this operation is undefined if the specified collection is
129	* modified while the operation is in progress.
130	*
131	* <p>This implementation iterates over the specified collection,
132	* and adds each element returned by the iterator to this
133	* queue, in turn. A runtime exception encountered while
134	* trying to add an element (including, in particular, a
135	* <tt>null</tt> element) may result in only some of the elements
136	* having been successfully added when the associated exception is
137	* thrown.
138	*
139	* @param c collection containing elements to be added to this queue
140	* @return <tt>true</tt> if this queue changed as a result of the call
141	* @throws ClassCastException if the class of an element of the specified
142	* collection prevents it from being added to this queue
143	* @throws NullPointerException if the specified collection contains a
144	* null element and this queue does not permit null elements,
145	* or if the specified collection is null
146	* @throws IllegalArgumentException if some property of an element of the
147	* specified collection prevents it from being added to this
148	* queue, or if the specified collection is this queue
149	* @throws IllegalStateException if not all the elements can be added at
150	* this time due to insertion restrictions
151	* @see #add(Object)
152	*/
153	public boolean addAll(Collection<? extends E> c) {
154	if (c == null)
155	throw new NullPointerException();
156	if (c == this)
157	throw new IllegalArgumentException();
158	boolean modified = false;
159	Iterator<? extends E> e = c.iterator();
160	while (e.hasNext()) {
161	if (add(e.next()))
162	modified = true;
163	}
164	return modified;
165	}
166
167	}