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. |
3 |
> |
* Expert Group and released to the public domain, as explained at |
4 |
> |
* http://creativecommons.org/licenses/publicdomain |
5 |
|
*/ |
6 |
|
|
7 |
|
package java.util; |
8 |
|
|
9 |
|
/** |
10 |
< |
* AbstractQueue provides default implementations of add, remove, and |
11 |
< |
* element based on offer, poll, and peek, respectively but that throw |
12 |
< |
* exceptions instead of indicating failure via false or null returns. |
13 |
< |
* The provided implementations all assume that the base implementation |
14 |
< |
* does <em>not</em> allow <tt>null</tt> elements. |
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 |
> |
* <p>This class is a member of the |
29 |
> |
* <a href="{@docRoot}/../guide/collections/index.html"> |
30 |
> |
* Java Collections Framework</a>. |
31 |
> |
* |
32 |
|
* @since 1.5 |
33 |
|
* @author Doug Lea |
34 |
+ |
* @param <E> the type of elements held in this collection |
35 |
|
*/ |
36 |
+ |
public abstract class AbstractQueue<E> |
37 |
+ |
extends AbstractCollection<E> |
38 |
+ |
implements Queue<E> { |
39 |
+ |
|
40 |
+ |
/** |
41 |
+ |
* Constructor for use by subclasses. |
42 |
+ |
*/ |
43 |
+ |
protected AbstractQueue() { |
44 |
+ |
} |
45 |
|
|
19 |
– |
public abstract class AbstractQueue<E> extends AbstractCollection<E> implements Queue<E> { |
46 |
|
|
47 |
< |
public boolean add(E x) { |
48 |
< |
if (offer(x)) |
47 |
> |
/** |
48 |
> |
* Adds the specified element to this queue. This implementation |
49 |
> |
* returns <tt>true</tt> if <tt>offer</tt> succeeds, else |
50 |
> |
* throws an IllegalStateException. |
51 |
> |
* |
52 |
> |
* @param o the element |
53 |
> |
* @return <tt>true</tt> (as per the general contract of |
54 |
> |
* <tt>Collection.add</tt>). |
55 |
> |
* |
56 |
> |
* @throws NullPointerException if the specified element is <tt>null</tt> |
57 |
> |
* @throws IllegalStateException if element cannot be added |
58 |
> |
*/ |
59 |
> |
public boolean add(E o) { |
60 |
> |
if (offer(o)) |
61 |
|
return true; |
62 |
|
else |
63 |
|
throw new IllegalStateException("Queue full"); |
64 |
|
} |
65 |
|
|
66 |
+ |
/** |
67 |
+ |
* Retrieves and removes the head of this queue. |
68 |
+ |
* This implementation returns the result of <tt>poll</tt> |
69 |
+ |
* unless the queue is empty. |
70 |
+ |
* |
71 |
+ |
* @return the head of this queue. |
72 |
+ |
* @throws NoSuchElementException if this queue is empty. |
73 |
+ |
*/ |
74 |
|
public E remove() { |
75 |
|
E x = poll(); |
76 |
|
if (x != null) |
79 |
|
throw new NoSuchElementException(); |
80 |
|
} |
81 |
|
|
82 |
+ |
|
83 |
+ |
/** |
84 |
+ |
* Retrieves, but does not remove, the head of this queue. |
85 |
+ |
* This implementation returns the result of <tt>peek</tt> |
86 |
+ |
* unless the queue is empty. |
87 |
+ |
* |
88 |
+ |
* @return the head of this queue. |
89 |
+ |
* @throws NoSuchElementException if this queue is empty. |
90 |
+ |
*/ |
91 |
|
public E element() { |
92 |
|
E x = peek(); |
93 |
|
if (x != null) |
96 |
|
throw new NoSuchElementException(); |
97 |
|
} |
98 |
|
|
99 |
+ |
/** |
100 |
+ |
* Removes all of the elements from this collection. |
101 |
+ |
* The collection will be empty after this call returns. |
102 |
+ |
* <p>This implementation repeatedly invokes {@link #poll poll} until it |
103 |
+ |
* returns <tt>null</tt>. |
104 |
+ |
*/ |
105 |
|
public void clear() { |
106 |
|
while (poll() != null) |
107 |
|
; |
108 |
|
} |
109 |
|
|
110 |
< |
// XXX Remove this redundant declaration, pending response from Neal Gafter. |
111 |
< |
public abstract Iterator<E> iterator(); |
112 |
< |
} |
113 |
< |
|
114 |
< |
|
115 |
< |
|
116 |
< |
|
110 |
> |
/** |
111 |
> |
* Adds all of the elements in the specified collection to this |
112 |
> |
* queue. Attempts to addAll of a queue to itself result in |
113 |
> |
* <tt>IllegalArgumentException</tt>. Further, the behavior of |
114 |
> |
* this operation is undefined if the specified collection is |
115 |
> |
* modified while the operation is in progress. |
116 |
> |
* |
117 |
> |
* <p>This implementation iterates over the specified collection, |
118 |
> |
* and adds each element returned by the iterator to this |
119 |
> |
* collection, in turn. A runtime exception encountered while |
120 |
> |
* trying to add an element (including, in particular, a |
121 |
> |
* <tt>null</tt> element) may result in only some of the elements |
122 |
> |
* having been successfully added when the associated exception is |
123 |
> |
* thrown. |
124 |
> |
* |
125 |
> |
* @param c collection whose elements are to be added to this collection. |
126 |
> |
* @return <tt>true</tt> if this collection changed as a result of the |
127 |
> |
* call. |
128 |
> |
* @throws NullPointerException if the specified collection or |
129 |
> |
* any of its elements are null. |
130 |
> |
* @throws IllegalArgumentException if c is this queue. |
131 |
> |
* |
132 |
> |
* @see #add(Object) |
133 |
> |
*/ |
134 |
> |
public boolean addAll(Collection<? extends E> c) { |
135 |
> |
if (c == null) |
136 |
> |
throw new NullPointerException(); |
137 |
> |
if (c == this) |
138 |
> |
throw new IllegalArgumentException(); |
139 |
> |
boolean modified = false; |
140 |
> |
Iterator<? extends E> e = c.iterator(); |
141 |
> |
while (e.hasNext()) { |
142 |
> |
if (add(e.next())) |
143 |
> |
modified = true; |
144 |
> |
} |
145 |
> |
return modified; |
146 |
> |
} |
147 |
|
|
148 |
+ |
} |