java/util/AbstractQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

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}.
 *
 * @since 1.5
 * @author Doug Lea
 */
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:	1.19
Committed:	Sun Oct 5 22:59:21 2003 UTC (20 years, 7 months ago) by dl
Branch:	MAIN
Changes since 1.18:	+39 -0 lines
Log Message:	addAll(self) throws exception; javadoc touchups
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain. Use, modify, and
4	* redistribute this code in any way without acknowledgement.
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	* @since 1.5
29	* @author Doug Lea
30	*/
31	public abstract class AbstractQueue<E>
32	extends AbstractCollection<E>
33	implements Queue<E> {
34
35	/**
36	* Constructor for use by subclasses.
37	*/
38	protected AbstractQueue() {
39	}
40
41
42	/**
43	* Adds the specified element to this queue. This implementation
44	* returns <tt>true</tt> if <tt>offer</tt> succeeds, else
45	* throws an IllegalStateException.
46	*
47	* @param o the element
48	* @return <tt>true</tt> (as per the general contract of
49	* <tt>Collection.add</tt>).
50	*
51	* @throws NullPointerException if the specified element is <tt>null</tt>
52	* @throws IllegalStateException if element cannot be added
53	*/
54	public boolean add(E o) {
55	if (offer(o))
56	return true;
57	else
58	throw new IllegalStateException("Queue full");
59	}
60
61	/**
62	* Retrieves and removes the head of this queue.
63	* This implementation returns the result of <tt>poll</tt>
64	* unless the queue is empty.
65	*
66	* @return the head of this queue.
67	* @throws NoSuchElementException if this queue is empty.
68	*/
69	public E remove() {
70	E x = poll();
71	if (x != null)
72	return x;
73	else
74	throw new NoSuchElementException();
75	}
76
77
78	/**
79	* Retrieves, but does not remove, the head of this queue.
80	* This implementation returns the result of <tt>peek</tt>
81	* unless the queue is empty.
82	*
83	* @return the head of this queue.
84	* @throws NoSuchElementException if this queue is empty.
85	*/
86	public E element() {
87	E x = peek();
88	if (x != null)
89	return x;
90	else
91	throw new NoSuchElementException();
92	}
93
94	/**
95	* Removes all of the elements from this collection.
96	* The collection will be empty after this call returns.
97	* <p>This implementation repeatedly invokes {@link #poll poll} until it
98	* returns <tt>null</tt>.
99	*/
100	public void clear() {
101	while (poll() != null)
102	;
103	}
104
105	/**
106	* Adds all of the elements in the specified collection to this
107	* queue. Attempts to addAll of a queue to itself result in
108	* <tt>IllegalArgumentException</tt>. Further, the behavior of
109	* this operation is undefined if the specified collection is
110	* modified while the operation is in progress.
111	*
112	* <p>This implementation iterates over the specified collection,
113	* and adds each element returned by the iterator to this
114	* collection, in turn. A runtime exception encountered while
115	* trying to add an element (including, in particular, a
116	* <tt>null</tt> element) may result in only some of the elements
117	* having been successfully added when the associated exception is
118	* thrown.
119	*
120	* @param c collection whose elements are to be added to this collection.
121	* @return <tt>true</tt> if this collection changed as a result of the
122	* call.
123	* @throws NullPointerException if the specified collection, or
124	* any of its elements are null.
125	* @throws IllegalArgumentException if c is this queue.
126	*
127	* @see #add(Object)
128	*/
129	public boolean addAll(Collection<? extends E> c) {
130	if (c == null)
131	throw new NullPointerException();
132	if (c == this)
133	throw new IllegalArgumentException();
134	boolean modified = false;
135	Iterator<? extends E> e = c.iterator();
136	while (e.hasNext()) {
137	if (add(e.next()))
138	modified = true;
139	}
140	return modified;
141	}
142
143	}