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/publicdomain/zero/1.0/
 */

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 {@code null}
 * 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 {@code false} or
 * {@code null} returns.
 *
 * <p>A {@code Queue} implementation that extends this class must
 * minimally define a method {@link Queue#offer} which does not permit
 * insertion of {@code null} elements, along with methods {@link
 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
 * {@link Collection#iterator}.  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}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this queue
 */
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
     * {@code true} upon success and throwing an {@code IllegalStateException}
     * if no space is currently available.
     *
     * <p>This implementation returns {@code true} if {@code offer} succeeds,
     * else throws an {@code IllegalStateException}.
     *
     * @param e the element to add
     * @return {@code true} (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 does 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 {@code poll}
     * 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 {@code peek}
     * 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 {@code null}.
     */
    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
     * {@code IllegalArgumentException}. 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
     * {@code null} 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 {@code true} 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;
        for (E e : c)
            if (add(e))
                modified = true;
        return modified;
    }

}
Revision:	1.1
Committed:	Sat Mar 26 06:22:49 2016 UTC (8 years ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	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/publicdomain/zero/1.0/
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 {@code null}
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 {@code false} or
17	* {@code null} returns.
18	*
19	* <p>A {@code Queue} implementation that extends this class must
20	* minimally define a method {@link Queue#offer} which does not permit
21	* insertion of {@code null} elements, along with methods {@link
22	* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
23	* {@link Collection#iterator}. Typically, additional methods will be
24	* overridden as well. If these requirements cannot be met, consider
25	* instead subclassing {@link AbstractCollection}.
26	*
27	* <p>This class is a member of the
28	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
29	* Java Collections Framework</a>.
30	*
31	* @since 1.5
32	* @author Doug Lea
33	* @param <E> the type of elements held in this queue
34	*/
35	public abstract class AbstractQueue<E>
36	extends AbstractCollection<E>
37	implements Queue<E> {
38
39	/**
40	* Constructor for use by subclasses.
41	*/
42	protected AbstractQueue() {
43	}
44
45	/**
46	* Inserts the specified element into this queue if it is possible to do so
47	* immediately without violating capacity restrictions, returning
48	* {@code true} upon success and throwing an {@code IllegalStateException}
49	* if no space is currently available.
50	*
51	* <p>This implementation returns {@code true} if {@code offer} succeeds,
52	* else throws an {@code IllegalStateException}.
53	*
54	* @param e the element to add
55	* @return {@code true} (as specified by {@link Collection#add})
56	* @throws IllegalStateException if the element cannot be added at this
57	* time due to capacity restrictions
58	* @throws ClassCastException if the class of the specified element
59	* prevents it from being added to this queue
60	* @throws NullPointerException if the specified element is null and
61	* this queue does not permit null elements
62	* @throws IllegalArgumentException if some property of this element
63	* prevents it from being added to this queue
64	*/
65	public boolean add(E e) {
66	if (offer(e))
67	return true;
68	else
69	throw new IllegalStateException("Queue full");
70	}
71
72	/**
73	* Retrieves and removes the head of this queue. This method differs
74	* from {@link #poll poll} only in that it throws an exception if this
75	* queue is empty.
76	*
77	* <p>This implementation returns the result of {@code poll}
78	* unless the queue is empty.
79	*
80	* @return the head of this queue
81	* @throws NoSuchElementException if this queue is empty
82	*/
83	public E remove() {
84	E x = poll();
85	if (x != null)
86	return x;
87	else
88	throw new NoSuchElementException();
89	}
90
91	/**
92	* Retrieves, but does not remove, the head of this queue. This method
93	* differs from {@link #peek peek} only in that it throws an exception if
94	* this queue is empty.
95	*
96	* <p>This implementation returns the result of {@code peek}
97	* unless the queue is empty.
98	*
99	* @return the head of this queue
100	* @throws NoSuchElementException if this queue is empty
101	*/
102	public E element() {
103	E x = peek();
104	if (x != null)
105	return x;
106	else
107	throw new NoSuchElementException();
108	}
109
110	/**
111	* Removes all of the elements from this queue.
112	* The queue will be empty after this call returns.
113	*
114	* <p>This implementation repeatedly invokes {@link #poll poll} until it
115	* returns {@code null}.
116	*/
117	public void clear() {
118	while (poll() != null)
119	;
120	}
121
122	/**
123	* Adds all of the elements in the specified collection to this
124	* queue. Attempts to addAll of a queue to itself result in
125	* {@code IllegalArgumentException}. Further, the behavior of
126	* this operation is undefined if the specified collection is
127	* modified while the operation is in progress.
128	*
129	* <p>This implementation iterates over the specified collection,
130	* and adds each element returned by the iterator to this
131	* queue, in turn. A runtime exception encountered while
132	* trying to add an element (including, in particular, a
133	* {@code null} element) may result in only some of the elements
134	* having been successfully added when the associated exception is
135	* thrown.
136	*
137	* @param c collection containing elements to be added to this queue
138	* @return {@code true} if this queue changed as a result of the call
139	* @throws ClassCastException if the class of an element of the specified
140	* collection prevents it from being added to this queue
141	* @throws NullPointerException if the specified collection contains a
142	* null element and this queue does not permit null elements,
143	* or if the specified collection is null
144	* @throws IllegalArgumentException if some property of an element of the
145	* specified collection prevents it from being added to this
146	* queue, or if the specified collection is this queue
147	* @throws IllegalStateException if not all the elements can be added at
148	* this time due to insertion restrictions
149	* @see #add(Object)
150	*/
151	public boolean addAll(Collection<? extends E> c) {
152	if (c == null)
153	throw new NullPointerException();
154	if (c == this)
155	throw new IllegalArgumentException();
156	boolean modified = false;
157	for (E e : c)
158	if (add(e))
159	modified = true;
160	return modified;
161	}
162
163	}