18 |
|
* implementations; in most implementations, insert operations cannot |
19 |
|
* fail. |
20 |
|
* |
21 |
< |
* <p><table BORDER CELLPADDING=3 CELLSPACING=1> |
21 |
> |
* <p> |
22 |
> |
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
23 |
|
* <tr> |
24 |
|
* <td></td> |
25 |
|
* <td ALIGN=CENTER><em>Throws exception</em></td> |
113 |
|
* @param <E> the type of elements held in this collection |
114 |
|
*/ |
115 |
|
public interface Queue<E> extends Collection<E> { |
115 |
– |
|
116 |
|
/** |
117 |
< |
* Inserts the specified element into this queue, if possible. When |
118 |
< |
* using queues that may impose insertion restrictions (for |
119 |
< |
* example capacity bounds), method <tt>offer</tt> is generally |
120 |
< |
* preferable to method {@link Collection#add}, which can fail to |
121 |
< |
* insert an element only by throwing an exception. |
122 |
< |
* |
123 |
< |
* @param e the element to insert. |
124 |
< |
* @return <tt>true</tt> if it was possible to add the element to |
125 |
< |
* this queue, else <tt>false</tt> |
117 |
> |
* Inserts the specified element into this queue if it is possible to do so |
118 |
> |
* immediately without violating capacity restrictions, returning |
119 |
> |
* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> |
120 |
> |
* if no space is currently available. |
121 |
> |
* |
122 |
> |
* @param e the element to add |
123 |
> |
* @return <tt>true</tt> (as specified by {@link Collection#add}) |
124 |
> |
* @throws IllegalStateException if the element cannot be added at this |
125 |
> |
* time due to capacity restrictions |
126 |
> |
* @throws ClassCastException if the class of the specified element |
127 |
> |
* prevents it from being added to this queue |
128 |
> |
* @throws NullPointerException if the specified element is null and |
129 |
> |
* this queue not permit null elements |
130 |
> |
* @throws IllegalArgumentException if some property of this element |
131 |
> |
* prevents it from being added to this queue |
132 |
|
*/ |
133 |
< |
boolean offer(E e); |
133 |
> |
boolean add(E e); |
134 |
|
|
135 |
|
/** |
136 |
< |
* Retrieves and removes the head of this queue, or <tt>null</tt> |
137 |
< |
* if this queue is empty. |
136 |
> |
* Inserts the specified element into this queue if it is possible to do |
137 |
> |
* so immediately without violating capacity restrictions. |
138 |
> |
* When using a capacity-restricted queue, this method is generally |
139 |
> |
* preferable to {@link #add}, which can fail to insert an element only |
140 |
> |
* by throwing an exception. |
141 |
|
* |
142 |
< |
* @return the head of this queue, or <tt>null</tt> if this |
143 |
< |
* queue is empty. |
142 |
> |
* @param e the element to add |
143 |
> |
* @return <tt>true</tt> if the element was added to this queue, else |
144 |
> |
* <tt>false</tt> |
145 |
> |
* @throws ClassCastException if the class of the specified element |
146 |
> |
* prevents it from being added to this queue |
147 |
> |
* @throws NullPointerException if the specified element is null and |
148 |
> |
* this queue does not permit null elements |
149 |
> |
* @throws IllegalArgumentException if some property of this element |
150 |
> |
* prevents it from being added to this queue |
151 |
|
*/ |
152 |
< |
E poll(); |
152 |
> |
boolean offer(E e); |
153 |
|
|
154 |
|
/** |
155 |
< |
* Retrieves and removes the head of this queue. This method |
156 |
< |
* differs from the {@link #poll} method only in that it throws an |
157 |
< |
* exception if this queue is empty. |
155 |
> |
* Retrieves and removes the head of this queue. This method differs |
156 |
> |
* from {@link #poll poll} only in that it throws an exception if this |
157 |
> |
* queue is empty. |
158 |
|
* |
159 |
< |
* @return the head of this queue. |
160 |
< |
* @throws NoSuchElementException if this queue is empty. |
159 |
> |
* @return the head of this queue |
160 |
> |
* @throws NoSuchElementException if this queue is empty |
161 |
|
*/ |
162 |
|
E remove(); |
163 |
|
|
164 |
|
/** |
165 |
< |
* Retrieves, but does not remove, the head of this queue, |
166 |
< |
* returning <tt>null</tt> if this queue is empty. |
165 |
> |
* Retrieves and removes the head of this queue, |
166 |
> |
* or returns <tt>null</tt> if this queue is empty. |
167 |
|
* |
168 |
< |
* @return the head of this queue, or <tt>null</tt> if this queue |
153 |
< |
* is empty. |
168 |
> |
* @return the head of this queue, or <tt>null</tt> if this queue is empty |
169 |
|
*/ |
170 |
< |
E peek(); |
170 |
> |
E poll(); |
171 |
|
|
172 |
|
/** |
173 |
|
* Retrieves, but does not remove, the head of this queue. This method |
174 |
< |
* differs from the {@link #peek} method only in that it throws an |
175 |
< |
* exception if this queue is empty. |
174 |
> |
* differs from {@link #peek peek} only in that it throws an exception |
175 |
> |
* if this queue is empty. |
176 |
|
* |
177 |
< |
* @return the head of this queue. |
178 |
< |
* @throws NoSuchElementException if this queue is empty. |
177 |
> |
* @return the head of this queue |
178 |
> |
* @throws NoSuchElementException if this queue is empty |
179 |
|
*/ |
180 |
|
E element(); |
181 |
+ |
|
182 |
+ |
/** |
183 |
+ |
* Retrieves, but does not remove, the head of this queue, |
184 |
+ |
* or returns <tt>null</tt> if this queue is empty. |
185 |
+ |
* |
186 |
+ |
* @return the head of this queue, or <tt>null</tt> if this queue is empty |
187 |
+ |
*/ |
188 |
+ |
E peek(); |
189 |
|
} |