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
7package java.util;
8
9// BEGIN android-note
10// removed link to collections framework docs
11// END android-note
12
13/**
14 * This class provides skeletal implementations of some {@link Queue}
15 * operations. The implementations in this class are appropriate when
16 * the base implementation does <em>not</em> allow <tt>null</tt>
17 * elements.  Methods {@link #add add}, {@link #remove remove}, and
18 * {@link #element element} are based on {@link #offer offer}, {@link
19 * #poll poll}, and {@link #peek peek}, respectively, but throw
20 * exceptions instead of indicating failure via <tt>false</tt> or
21 * <tt>null</tt> returns.
22 *
23 * <p>A <tt>Queue</tt> implementation that extends this class must
24 * minimally define a method {@link Queue#offer} which does not permit
25 * insertion of <tt>null</tt> elements, along with methods {@link
26 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
27 * {@link Collection#iterator}.  Typically, additional methods will be
28 * overridden as well.  If these requirements cannot be met, consider
29 * instead subclassing {@link AbstractCollection}.
30 *
31 * @since 1.5
32 * @author Doug Lea
33 * @param <E> the type of elements held in this collection
34 */
35public 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     * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
49     * if no space is currently available.
50     *
51     * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
52     * else throws an <tt>IllegalStateException</tt>.
53     *
54     * @param e the element to add
55     * @return <tt>true</tt> (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 <tt>poll</tt>
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 <tt>peek</tt>
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 <tt>null</tt>.
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     * <tt>IllegalArgumentException</tt>. 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     * <tt>null</tt> 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 <tt>true</tt> 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("c == null");
154        if (c == this)
155            throw new IllegalArgumentException("c == this");
156        boolean modified = false;
157        for (E e : c)
158            if (add(e))
159                modified = true;
160        return modified;
161    }
162
163}
164