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 |
* <tt>AbstractQueue</tt> provides default implementations of |
11 |
* {@link #add add}, {@link #remove remove}, and {@link #element element} |
12 |
* based on |
13 |
* {@link #offer offer}, {@link #poll poll}, and {@link #peek peek}, |
14 |
* respectively but that |
15 |
* throw exceptions instead of indicating failure via <tt>false</tt> or |
16 |
* <tt>null</tt> returns. |
17 |
* <p>The provided implementations all assume that the base implementation |
18 |
* does <em>not</em> allow <tt>null</tt> elements. |
19 |
* @since 1.5 |
20 |
* @author Doug Lea |
21 |
*/ |
22 |
public abstract class AbstractQueue<E> |
23 |
extends AbstractCollection<E> |
24 |
implements Queue<E> { |
25 |
|
26 |
// note that optional methods are not optional here or in our subclasses, |
27 |
// so we redefine each optional method to document that it is not optional |
28 |
// We also inherit, or define, all necessary @throws comments |
29 |
|
30 |
// /** |
31 |
// * @throws NullPointerException if the specified element is <tt>null</tt> |
32 |
// */ |
33 |
// public abstract boolean offer(E o); |
34 |
|
35 |
/** |
36 |
* Adds the specified element to this queue. |
37 |
* @return <tt>true</tt> (as per the general contract of |
38 |
* <tt>Collection.add</tt>). |
39 |
* |
40 |
* @throws NullPointerException if the specified element is <tt>null</tt> |
41 |
*/ |
42 |
public boolean add(E o) { |
43 |
if (offer(o)) |
44 |
return true; |
45 |
else |
46 |
throw new IllegalStateException("Queue full"); |
47 |
} |
48 |
|
49 |
/** |
50 |
* Adds all of the elements in the specified collection to this queue. |
51 |
* The behavior of this operation is undefined if |
52 |
* the specified collection is modified while the operation is in |
53 |
* progress. (This implies that the behavior of this call is undefined if |
54 |
* the specified collection is this queue, and this queue is nonempty.) |
55 |
* <p> |
56 |
* This implementation iterates over the specified collection, and adds |
57 |
* each object returned by the iterator to this queue, in turn. |
58 |
* |
59 |
* @param c collection whose elements are to be added to this queue |
60 |
* @return <tt>true</tt> if this collection changed as a result of the |
61 |
* call. |
62 |
* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt> |
63 |
* is <tt>null</tt> |
64 |
* |
65 |
*/ |
66 |
public boolean addAll(Collection<? extends E> c) { |
67 |
return super.addAll(c); |
68 |
} |
69 |
|
70 |
/** @throws NoSuchElementException {@inheritDoc} */ |
71 |
public E remove() { |
72 |
E x = poll(); |
73 |
if (x != null) |
74 |
return x; |
75 |
else |
76 |
throw new NoSuchElementException(); |
77 |
} |
78 |
|
79 |
/** @throws NoSuchElementException {@inheritDoc} */ |
80 |
public E element() { |
81 |
E x = peek(); |
82 |
if (x != null) |
83 |
return x; |
84 |
else |
85 |
throw new NoSuchElementException(); |
86 |
} |
87 |
|
88 |
/** |
89 |
* Removes all of the elements from this collection. |
90 |
* The collection will be empty after this call returns. |
91 |
* <p>This implementation repeatedly invokes {@link #poll poll} until it |
92 |
* returns <tt>null</tt>. |
93 |
*/ |
94 |
public void clear() { |
95 |
while (poll() != null) |
96 |
; |
97 |
} |
98 |
|
99 |
// XXX Remove this redundant declaration, pending response from Neal Gafter. |
100 |
public abstract Iterator<E> iterator(); |
101 |
} |
102 |
|
103 |
|
104 |
|
105 |
|
106 |
|