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}/java.base/java/util/package-summary.html#CollectionsFramework">
 * 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:	1.41
Committed:	Mon Oct 1 00:10:52 2018 UTC (5 years, 7 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.40:	+1 -1 lines
Log Message:	update to using jdk11 by default, except link to jdk10 javadocs; sync @docRoot references in javadoc with upstream
#	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	jsr166	1.37	* http://creativecommons.org/publicdomain/zero/1.0/
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	jsr166	1.38	* the base implementation does <em>not</em> allow {@code null}
13	dl	1.14	* elements. Methods {@link #add add}, {@link #remove remove}, and
14			* {@link #element element} are based on {@link #offer offer}, {@link
15	jsr166	1.35	* #poll poll}, and {@link #peek peek}, respectively, but throw
16	jsr166	1.38	* exceptions instead of indicating failure via {@code false} or
17			* {@code null} returns.
18	dl	1.14	*
19	jsr166	1.38	* <p>A {@code Queue} implementation that extends this class must
20	dl	1.14	* minimally define a method {@link Queue#offer} which does not permit
21	jsr166	1.38	* insertion of {@code null} elements, along with methods {@link
22	jsr166	1.35	* 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	dl	1.14	*
27	dl	1.25	* <p>This class is a member of the
28	jsr166	1.41	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
29	dl	1.25	* Java Collections Framework</a>.
30	jsr166	1.26	*
31	dl	1.4	* @since 1.5
32			* @author Doug Lea
33	jsr166	1.39	* @param <E> the type of elements held in this queue
34	tim	1.1	*/
35	tim	1.10	public abstract class AbstractQueue<E>
36			extends AbstractCollection<E>
37	dholmes	1.9	implements Queue<E> {
38	tim	1.5
39	dl	1.14	/**
40			* Constructor for use by subclasses.
41			*/
42			protected AbstractQueue() {
43			}
44	tim	1.1
45	dholmes	1.12	/**
46	jsr166	1.28	* Inserts the specified element into this queue if it is possible to do so
47			* immediately without violating capacity restrictions, returning
48	jsr166	1.38	* {@code true} upon success and throwing an {@code IllegalStateException}
49	jsr166	1.28	* if no space is currently available.
50			*
51	jsr166	1.38	* <p>This implementation returns {@code true} if {@code offer} succeeds,
52			* else throws an {@code IllegalStateException}.
53	jsr166	1.28	*
54			* @param e the element to add
55	jsr166	1.38	* @return {@code true} (as specified by {@link Collection#add})
56	jsr166	1.28	* @throws IllegalStateException if the element cannot be added at this
57			* time due to capacity restrictions
58	jsr166	1.29	* @throws ClassCastException if the class of the specified element
59			* prevents it from being added to this queue
60	jsr166	1.28	* @throws NullPointerException if the specified element is null and
61	jsr166	1.33	* this queue does not permit null elements
62	jsr166	1.28	* @throws IllegalArgumentException if some property of this element
63			* prevents it from being added to this queue
64	dholmes	1.9	*/
65	jsr166	1.27	public boolean add(E e) {
66			if (offer(e))
67	tim	1.1	return true;
68			else
69			throw new IllegalStateException("Queue full");
70			}
71
72	dholmes	1.9	/**
73	jsr166	1.28	* Retrieves and removes the head of this queue. This method differs
74	jsr166	1.31	* from {@link #poll poll} only in that it throws an exception if this
75			* queue is empty.
76	jsr166	1.28	*
77	jsr166	1.38	* <p>This implementation returns the result of {@code poll}
78	dl	1.14	* unless the queue is empty.
79	dholmes	1.9	*
80	jsr166	1.28	* @return the head of this queue
81			* @throws NoSuchElementException if this queue is empty
82	dholmes	1.9	*/
83	tim	1.8	public E remove() {
84	tim	1.1	E x = poll();
85			if (x != null)
86			return x;
87			else
88			throw new NoSuchElementException();
89			}
90
91	dl	1.14	/**
92	jsr166	1.28	* Retrieves, but does not remove, the head of this queue. This method
93	jsr166	1.31	* differs from {@link #peek peek} only in that it throws an exception if
94	jsr166	1.28	* this queue is empty.
95			*
96	jsr166	1.38	* <p>This implementation returns the result of {@code peek}
97	dl	1.14	* unless the queue is empty.
98			*
99	jsr166	1.28	* @return the head of this queue
100			* @throws NoSuchElementException if this queue is empty
101	dl	1.14	*/
102	tim	1.8	public E element() {
103	tim	1.1	E x = peek();
104			if (x != null)
105			return x;
106			else
107			throw new NoSuchElementException();
108			}
109
110	dholmes	1.9	/**
111	jsr166	1.26	* Removes all of the elements from this queue.
112			* The queue will be empty after this call returns.
113	jsr166	1.28	*
114	dholmes	1.9	* <p>This implementation repeatedly invokes {@link #poll poll} until it
115	jsr166	1.38	* returns {@code null}.
116	dholmes	1.9	*/
117	tim	1.1	public void clear() {
118			while (poll() != null)
119			;
120			}
121	dl	1.19
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	jsr166	1.38	* {@code IllegalArgumentException}. Further, the behavior of
126	dl	1.19	* 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	jsr166	1.26	* queue, in turn. A runtime exception encountered while
132	dl	1.19	* trying to add an element (including, in particular, a
133	jsr166	1.38	* {@code null} element) may result in only some of the elements
134	dl	1.19	* having been successfully added when the associated exception is
135			* thrown.
136			*
137	jsr166	1.30	* @param c collection containing elements to be added to this queue
138	jsr166	1.38	* @return {@code true} if this queue changed as a result of the call
139	jsr166	1.29	* @throws ClassCastException if the class of an element of the specified
140			* collection prevents it from being added to this queue
141	jsr166	1.28	* @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	jsr166	1.29	* specified collection prevents it from being added to this
146			* queue, or if the specified collection is this queue
147	jsr166	1.28	* @throws IllegalStateException if not all the elements can be added at
148			* this time due to insertion restrictions
149	dl	1.19	* @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	jozart	1.23	boolean modified = false;
157	jsr166	1.36	for (E e : c)
158			if (add(e))
159	jozart	1.23	modified = true;
160			return modified;
161	dl	1.19	}
162
163	dl	1.14	}