1 |
jsr166 |
1.1 |
/* |
2 |
|
|
* Written by Doug Lea and Josh Bloch with assistance from members of |
3 |
|
|
* JCP JSR-166 Expert Group and released to the public domain, as explained |
4 |
|
|
* at http://creativecommons.org/publicdomain/zero/1.0/ |
5 |
|
|
*/ |
6 |
|
|
|
7 |
|
|
package java.util; |
8 |
|
|
|
9 |
|
|
/** |
10 |
|
|
* A linear collection that supports element insertion and removal at |
11 |
|
|
* both ends. The name <i>deque</i> is short for "double ended queue" |
12 |
|
|
* and is usually pronounced "deck". Most {@code Deque} |
13 |
|
|
* implementations place no fixed limits on the number of elements |
14 |
|
|
* they may contain, but this interface supports capacity-restricted |
15 |
|
|
* deques as well as those with no fixed size limit. |
16 |
|
|
* |
17 |
|
|
* <p>This interface defines methods to access the elements at both |
18 |
|
|
* ends of the deque. Methods are provided to insert, remove, and |
19 |
|
|
* examine the element. Each of these methods exists in two forms: |
20 |
|
|
* one throws an exception if the operation fails, the other returns a |
21 |
|
|
* special value (either {@code null} or {@code false}, depending on |
22 |
|
|
* the operation). The latter form of the insert operation is |
23 |
|
|
* designed specifically for use with capacity-restricted |
24 |
|
|
* {@code Deque} implementations; in most implementations, insert |
25 |
|
|
* operations cannot fail. |
26 |
|
|
* |
27 |
|
|
* <p>The twelve methods described above are summarized in the |
28 |
|
|
* following table: |
29 |
|
|
* |
30 |
|
|
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
31 |
|
|
* <caption>Summary of Deque methods</caption> |
32 |
|
|
* <tr> |
33 |
|
|
* <td></td> |
34 |
|
|
* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td> |
35 |
|
|
* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td> |
36 |
|
|
* </tr> |
37 |
|
|
* <tr> |
38 |
|
|
* <td></td> |
39 |
|
|
* <td ALIGN=CENTER><em>Throws exception</em></td> |
40 |
|
|
* <td ALIGN=CENTER><em>Special value</em></td> |
41 |
|
|
* <td ALIGN=CENTER><em>Throws exception</em></td> |
42 |
|
|
* <td ALIGN=CENTER><em>Special value</em></td> |
43 |
|
|
* </tr> |
44 |
|
|
* <tr> |
45 |
|
|
* <td><b>Insert</b></td> |
46 |
|
|
* <td>{@link Deque#addFirst addFirst(e)}</td> |
47 |
|
|
* <td>{@link Deque#offerFirst offerFirst(e)}</td> |
48 |
|
|
* <td>{@link Deque#addLast addLast(e)}</td> |
49 |
|
|
* <td>{@link Deque#offerLast offerLast(e)}</td> |
50 |
|
|
* </tr> |
51 |
|
|
* <tr> |
52 |
|
|
* <td><b>Remove</b></td> |
53 |
|
|
* <td>{@link Deque#removeFirst removeFirst()}</td> |
54 |
|
|
* <td>{@link Deque#pollFirst pollFirst()}</td> |
55 |
|
|
* <td>{@link Deque#removeLast removeLast()}</td> |
56 |
|
|
* <td>{@link Deque#pollLast pollLast()}</td> |
57 |
|
|
* </tr> |
58 |
|
|
* <tr> |
59 |
|
|
* <td><b>Examine</b></td> |
60 |
|
|
* <td>{@link Deque#getFirst getFirst()}</td> |
61 |
|
|
* <td>{@link Deque#peekFirst peekFirst()}</td> |
62 |
|
|
* <td>{@link Deque#getLast getLast()}</td> |
63 |
|
|
* <td>{@link Deque#peekLast peekLast()}</td> |
64 |
|
|
* </tr> |
65 |
|
|
* </table> |
66 |
|
|
* |
67 |
|
|
* <p>This interface extends the {@link Queue} interface. When a deque is |
68 |
|
|
* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are |
69 |
|
|
* added at the end of the deque and removed from the beginning. The methods |
70 |
|
|
* inherited from the {@code Queue} interface are precisely equivalent to |
71 |
|
|
* {@code Deque} methods as indicated in the following table: |
72 |
|
|
* |
73 |
|
|
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
74 |
|
|
* <caption>Comparison of Queue and Deque methods</caption> |
75 |
|
|
* <tr> |
76 |
|
|
* <td ALIGN=CENTER> <b>{@code Queue} Method</b></td> |
77 |
|
|
* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
78 |
|
|
* </tr> |
79 |
|
|
* <tr> |
80 |
|
|
* <td>{@link java.util.Queue#add add(e)}</td> |
81 |
|
|
* <td>{@link #addLast addLast(e)}</td> |
82 |
|
|
* </tr> |
83 |
|
|
* <tr> |
84 |
|
|
* <td>{@link java.util.Queue#offer offer(e)}</td> |
85 |
|
|
* <td>{@link #offerLast offerLast(e)}</td> |
86 |
|
|
* </tr> |
87 |
|
|
* <tr> |
88 |
|
|
* <td>{@link java.util.Queue#remove remove()}</td> |
89 |
|
|
* <td>{@link #removeFirst removeFirst()}</td> |
90 |
|
|
* </tr> |
91 |
|
|
* <tr> |
92 |
|
|
* <td>{@link java.util.Queue#poll poll()}</td> |
93 |
|
|
* <td>{@link #pollFirst pollFirst()}</td> |
94 |
|
|
* </tr> |
95 |
|
|
* <tr> |
96 |
|
|
* <td>{@link java.util.Queue#element element()}</td> |
97 |
|
|
* <td>{@link #getFirst getFirst()}</td> |
98 |
|
|
* </tr> |
99 |
|
|
* <tr> |
100 |
|
|
* <td>{@link java.util.Queue#peek peek()}</td> |
101 |
|
|
* <td>{@link #peek peekFirst()}</td> |
102 |
|
|
* </tr> |
103 |
|
|
* </table> |
104 |
|
|
* |
105 |
|
|
* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This |
106 |
|
|
* interface should be used in preference to the legacy {@link Stack} class. |
107 |
|
|
* When a deque is used as a stack, elements are pushed and popped from the |
108 |
|
|
* beginning of the deque. Stack methods are precisely equivalent to |
109 |
|
|
* {@code Deque} methods as indicated in the table below: |
110 |
|
|
* |
111 |
|
|
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
112 |
|
|
* <caption>Comparison of Stack and Deque methods</caption> |
113 |
|
|
* <tr> |
114 |
|
|
* <td ALIGN=CENTER> <b>Stack Method</b></td> |
115 |
|
|
* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
116 |
|
|
* </tr> |
117 |
|
|
* <tr> |
118 |
|
|
* <td>{@link #push push(e)}</td> |
119 |
|
|
* <td>{@link #addFirst addFirst(e)}</td> |
120 |
|
|
* </tr> |
121 |
|
|
* <tr> |
122 |
|
|
* <td>{@link #pop pop()}</td> |
123 |
|
|
* <td>{@link #removeFirst removeFirst()}</td> |
124 |
|
|
* </tr> |
125 |
|
|
* <tr> |
126 |
|
|
* <td>{@link #peek peek()}</td> |
127 |
|
|
* <td>{@link #peekFirst peekFirst()}</td> |
128 |
|
|
* </tr> |
129 |
|
|
* </table> |
130 |
|
|
* |
131 |
|
|
* <p>Note that the {@link #peek peek} method works equally well when |
132 |
|
|
* a deque is used as a queue or a stack; in either case, elements are |
133 |
|
|
* drawn from the beginning of the deque. |
134 |
|
|
* |
135 |
|
|
* <p>This interface provides two methods to remove interior |
136 |
|
|
* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and |
137 |
|
|
* {@link #removeLastOccurrence removeLastOccurrence}. |
138 |
|
|
* |
139 |
|
|
* <p>Unlike the {@link List} interface, this interface does not |
140 |
|
|
* provide support for indexed access to elements. |
141 |
|
|
* |
142 |
|
|
* <p>While {@code Deque} implementations are not strictly required |
143 |
|
|
* to prohibit the insertion of null elements, they are strongly |
144 |
|
|
* encouraged to do so. Users of any {@code Deque} implementations |
145 |
|
|
* that do allow null elements are strongly encouraged <i>not</i> to |
146 |
|
|
* take advantage of the ability to insert nulls. This is so because |
147 |
|
|
* {@code null} is used as a special return value by various methods |
148 |
|
|
* to indicate that the deque is empty. |
149 |
|
|
* |
150 |
|
|
* <p>{@code Deque} implementations generally do not define |
151 |
|
|
* element-based versions of the {@code equals} and {@code hashCode} |
152 |
|
|
* methods, but instead inherit the identity-based versions from class |
153 |
|
|
* {@code Object}. |
154 |
|
|
* |
155 |
|
|
* <p>This interface is a member of the <a |
156 |
|
|
* href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections |
157 |
|
|
* Framework</a>. |
158 |
|
|
* |
159 |
|
|
* @author Doug Lea |
160 |
|
|
* @author Josh Bloch |
161 |
|
|
* @since 1.6 |
162 |
|
|
* @param <E> the type of elements held in this deque |
163 |
|
|
*/ |
164 |
|
|
public interface Deque<E> extends Queue<E> { |
165 |
|
|
/** |
166 |
|
|
* Inserts the specified element at the front of this deque if it is |
167 |
|
|
* possible to do so immediately without violating capacity restrictions, |
168 |
|
|
* throwing an {@code IllegalStateException} if no space is currently |
169 |
|
|
* available. When using a capacity-restricted deque, it is generally |
170 |
|
|
* preferable to use method {@link #offerFirst}. |
171 |
|
|
* |
172 |
|
|
* @param e the element to add |
173 |
|
|
* @throws IllegalStateException if the element cannot be added at this |
174 |
|
|
* time due to capacity restrictions |
175 |
|
|
* @throws ClassCastException if the class of the specified element |
176 |
|
|
* prevents it from being added to this deque |
177 |
|
|
* @throws NullPointerException if the specified element is null and this |
178 |
|
|
* deque does not permit null elements |
179 |
|
|
* @throws IllegalArgumentException if some property of the specified |
180 |
|
|
* element prevents it from being added to this deque |
181 |
|
|
*/ |
182 |
|
|
void addFirst(E e); |
183 |
|
|
|
184 |
|
|
/** |
185 |
|
|
* Inserts the specified element at the end of this deque if it is |
186 |
|
|
* possible to do so immediately without violating capacity restrictions, |
187 |
|
|
* throwing an {@code IllegalStateException} if no space is currently |
188 |
|
|
* available. When using a capacity-restricted deque, it is generally |
189 |
|
|
* preferable to use method {@link #offerLast}. |
190 |
|
|
* |
191 |
|
|
* <p>This method is equivalent to {@link #add}. |
192 |
|
|
* |
193 |
|
|
* @param e the element to add |
194 |
|
|
* @throws IllegalStateException if the element cannot be added at this |
195 |
|
|
* time due to capacity restrictions |
196 |
|
|
* @throws ClassCastException if the class of the specified element |
197 |
|
|
* prevents it from being added to this deque |
198 |
|
|
* @throws NullPointerException if the specified element is null and this |
199 |
|
|
* deque does not permit null elements |
200 |
|
|
* @throws IllegalArgumentException if some property of the specified |
201 |
|
|
* element prevents it from being added to this deque |
202 |
|
|
*/ |
203 |
|
|
void addLast(E e); |
204 |
|
|
|
205 |
|
|
/** |
206 |
|
|
* Inserts the specified element at the front of this deque unless it would |
207 |
|
|
* violate capacity restrictions. When using a capacity-restricted deque, |
208 |
|
|
* this method is generally preferable to the {@link #addFirst} method, |
209 |
|
|
* which can fail to insert an element only by throwing an exception. |
210 |
|
|
* |
211 |
|
|
* @param e the element to add |
212 |
|
|
* @return {@code true} if the element was added to this deque, else |
213 |
|
|
* {@code false} |
214 |
|
|
* @throws ClassCastException if the class of the specified element |
215 |
|
|
* prevents it from being added to this deque |
216 |
|
|
* @throws NullPointerException if the specified element is null and this |
217 |
|
|
* deque does not permit null elements |
218 |
|
|
* @throws IllegalArgumentException if some property of the specified |
219 |
|
|
* element prevents it from being added to this deque |
220 |
|
|
*/ |
221 |
|
|
boolean offerFirst(E e); |
222 |
|
|
|
223 |
|
|
/** |
224 |
|
|
* Inserts the specified element at the end of this deque unless it would |
225 |
|
|
* violate capacity restrictions. When using a capacity-restricted deque, |
226 |
|
|
* this method is generally preferable to the {@link #addLast} method, |
227 |
|
|
* which can fail to insert an element only by throwing an exception. |
228 |
|
|
* |
229 |
|
|
* @param e the element to add |
230 |
|
|
* @return {@code true} if the element was added to this deque, else |
231 |
|
|
* {@code false} |
232 |
|
|
* @throws ClassCastException if the class of the specified element |
233 |
|
|
* prevents it from being added to this deque |
234 |
|
|
* @throws NullPointerException if the specified element is null and this |
235 |
|
|
* deque does not permit null elements |
236 |
|
|
* @throws IllegalArgumentException if some property of the specified |
237 |
|
|
* element prevents it from being added to this deque |
238 |
|
|
*/ |
239 |
|
|
boolean offerLast(E e); |
240 |
|
|
|
241 |
|
|
/** |
242 |
|
|
* Retrieves and removes the first element of this deque. This method |
243 |
|
|
* differs from {@link #pollFirst pollFirst} only in that it throws an |
244 |
|
|
* exception if this deque is empty. |
245 |
|
|
* |
246 |
|
|
* @return the head of this deque |
247 |
|
|
* @throws NoSuchElementException if this deque is empty |
248 |
|
|
*/ |
249 |
|
|
E removeFirst(); |
250 |
|
|
|
251 |
|
|
/** |
252 |
|
|
* Retrieves and removes the last element of this deque. This method |
253 |
|
|
* differs from {@link #pollLast pollLast} only in that it throws an |
254 |
|
|
* exception if this deque is empty. |
255 |
|
|
* |
256 |
|
|
* @return the tail of this deque |
257 |
|
|
* @throws NoSuchElementException if this deque is empty |
258 |
|
|
*/ |
259 |
|
|
E removeLast(); |
260 |
|
|
|
261 |
|
|
/** |
262 |
|
|
* Retrieves and removes the first element of this deque, |
263 |
|
|
* or returns {@code null} if this deque is empty. |
264 |
|
|
* |
265 |
|
|
* @return the head of this deque, or {@code null} if this deque is empty |
266 |
|
|
*/ |
267 |
|
|
E pollFirst(); |
268 |
|
|
|
269 |
|
|
/** |
270 |
|
|
* Retrieves and removes the last element of this deque, |
271 |
|
|
* or returns {@code null} if this deque is empty. |
272 |
|
|
* |
273 |
|
|
* @return the tail of this deque, or {@code null} if this deque is empty |
274 |
|
|
*/ |
275 |
|
|
E pollLast(); |
276 |
|
|
|
277 |
|
|
/** |
278 |
|
|
* Retrieves, but does not remove, the first element of this deque. |
279 |
|
|
* |
280 |
|
|
* This method differs from {@link #peekFirst peekFirst} only in that it |
281 |
|
|
* throws an exception if this deque is empty. |
282 |
|
|
* |
283 |
|
|
* @return the head of this deque |
284 |
|
|
* @throws NoSuchElementException if this deque is empty |
285 |
|
|
*/ |
286 |
|
|
E getFirst(); |
287 |
|
|
|
288 |
|
|
/** |
289 |
|
|
* Retrieves, but does not remove, the last element of this deque. |
290 |
|
|
* This method differs from {@link #peekLast peekLast} only in that it |
291 |
|
|
* throws an exception if this deque is empty. |
292 |
|
|
* |
293 |
|
|
* @return the tail of this deque |
294 |
|
|
* @throws NoSuchElementException if this deque is empty |
295 |
|
|
*/ |
296 |
|
|
E getLast(); |
297 |
|
|
|
298 |
|
|
/** |
299 |
|
|
* Retrieves, but does not remove, the first element of this deque, |
300 |
|
|
* or returns {@code null} if this deque is empty. |
301 |
|
|
* |
302 |
|
|
* @return the head of this deque, or {@code null} if this deque is empty |
303 |
|
|
*/ |
304 |
|
|
E peekFirst(); |
305 |
|
|
|
306 |
|
|
/** |
307 |
|
|
* Retrieves, but does not remove, the last element of this deque, |
308 |
|
|
* or returns {@code null} if this deque is empty. |
309 |
|
|
* |
310 |
|
|
* @return the tail of this deque, or {@code null} if this deque is empty |
311 |
|
|
*/ |
312 |
|
|
E peekLast(); |
313 |
|
|
|
314 |
|
|
/** |
315 |
|
|
* Removes the first occurrence of the specified element from this deque. |
316 |
|
|
* If the deque does not contain the element, it is unchanged. |
317 |
|
|
* More formally, removes the first element {@code e} such that |
318 |
|
|
* {@code Objects.equals(o, e)} (if such an element exists). |
319 |
|
|
* Returns {@code true} if this deque contained the specified element |
320 |
|
|
* (or equivalently, if this deque changed as a result of the call). |
321 |
|
|
* |
322 |
|
|
* @param o element to be removed from this deque, if present |
323 |
|
|
* @return {@code true} if an element was removed as a result of this call |
324 |
|
|
* @throws ClassCastException if the class of the specified element |
325 |
|
|
* is incompatible with this deque |
326 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
327 |
|
|
* @throws NullPointerException if the specified element is null and this |
328 |
|
|
* deque does not permit null elements |
329 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
330 |
|
|
*/ |
331 |
|
|
boolean removeFirstOccurrence(Object o); |
332 |
|
|
|
333 |
|
|
/** |
334 |
|
|
* Removes the last occurrence of the specified element from this deque. |
335 |
|
|
* If the deque does not contain the element, it is unchanged. |
336 |
|
|
* More formally, removes the last element {@code e} such that |
337 |
|
|
* {@code Objects.equals(o, e)} (if such an element exists). |
338 |
|
|
* Returns {@code true} if this deque contained the specified element |
339 |
|
|
* (or equivalently, if this deque changed as a result of the call). |
340 |
|
|
* |
341 |
|
|
* @param o element to be removed from this deque, if present |
342 |
|
|
* @return {@code true} if an element was removed as a result of this call |
343 |
|
|
* @throws ClassCastException if the class of the specified element |
344 |
|
|
* is incompatible with this deque |
345 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
346 |
|
|
* @throws NullPointerException if the specified element is null and this |
347 |
|
|
* deque does not permit null elements |
348 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
349 |
|
|
*/ |
350 |
|
|
boolean removeLastOccurrence(Object o); |
351 |
|
|
|
352 |
|
|
// *** Queue methods *** |
353 |
|
|
|
354 |
|
|
/** |
355 |
|
|
* Inserts the specified element into the queue represented by this deque |
356 |
|
|
* (in other words, at the tail of this deque) if it is possible to do so |
357 |
|
|
* immediately without violating capacity restrictions, returning |
358 |
|
|
* {@code true} upon success and throwing an |
359 |
|
|
* {@code IllegalStateException} if no space is currently available. |
360 |
|
|
* When using a capacity-restricted deque, it is generally preferable to |
361 |
|
|
* use {@link #offer(Object) offer}. |
362 |
|
|
* |
363 |
|
|
* <p>This method is equivalent to {@link #addLast}. |
364 |
|
|
* |
365 |
|
|
* @param e the element to add |
366 |
|
|
* @return {@code true} (as specified by {@link Collection#add}) |
367 |
|
|
* @throws IllegalStateException if the element cannot be added at this |
368 |
|
|
* time due to capacity restrictions |
369 |
|
|
* @throws ClassCastException if the class of the specified element |
370 |
|
|
* prevents it from being added to this deque |
371 |
|
|
* @throws NullPointerException if the specified element is null and this |
372 |
|
|
* deque does not permit null elements |
373 |
|
|
* @throws IllegalArgumentException if some property of the specified |
374 |
|
|
* element prevents it from being added to this deque |
375 |
|
|
*/ |
376 |
|
|
boolean add(E e); |
377 |
|
|
|
378 |
|
|
/** |
379 |
|
|
* Inserts the specified element into the queue represented by this deque |
380 |
|
|
* (in other words, at the tail of this deque) if it is possible to do so |
381 |
|
|
* immediately without violating capacity restrictions, returning |
382 |
|
|
* {@code true} upon success and {@code false} if no space is currently |
383 |
|
|
* available. When using a capacity-restricted deque, this method is |
384 |
|
|
* generally preferable to the {@link #add} method, which can fail to |
385 |
|
|
* insert an element only by throwing an exception. |
386 |
|
|
* |
387 |
|
|
* <p>This method is equivalent to {@link #offerLast}. |
388 |
|
|
* |
389 |
|
|
* @param e the element to add |
390 |
|
|
* @return {@code true} if the element was added to this deque, else |
391 |
|
|
* {@code false} |
392 |
|
|
* @throws ClassCastException if the class of the specified element |
393 |
|
|
* prevents it from being added to this deque |
394 |
|
|
* @throws NullPointerException if the specified element is null and this |
395 |
|
|
* deque does not permit null elements |
396 |
|
|
* @throws IllegalArgumentException if some property of the specified |
397 |
|
|
* element prevents it from being added to this deque |
398 |
|
|
*/ |
399 |
|
|
boolean offer(E e); |
400 |
|
|
|
401 |
|
|
/** |
402 |
|
|
* Retrieves and removes the head of the queue represented by this deque |
403 |
|
|
* (in other words, the first element of this deque). |
404 |
|
|
* This method differs from {@link #poll poll} only in that it throws an |
405 |
|
|
* exception if this deque is empty. |
406 |
|
|
* |
407 |
|
|
* <p>This method is equivalent to {@link #removeFirst()}. |
408 |
|
|
* |
409 |
|
|
* @return the head of the queue represented by this deque |
410 |
|
|
* @throws NoSuchElementException if this deque is empty |
411 |
|
|
*/ |
412 |
|
|
E remove(); |
413 |
|
|
|
414 |
|
|
/** |
415 |
|
|
* Retrieves and removes the head of the queue represented by this deque |
416 |
|
|
* (in other words, the first element of this deque), or returns |
417 |
|
|
* {@code null} if this deque is empty. |
418 |
|
|
* |
419 |
|
|
* <p>This method is equivalent to {@link #pollFirst()}. |
420 |
|
|
* |
421 |
|
|
* @return the first element of this deque, or {@code null} if |
422 |
|
|
* this deque is empty |
423 |
|
|
*/ |
424 |
|
|
E poll(); |
425 |
|
|
|
426 |
|
|
/** |
427 |
|
|
* Retrieves, but does not remove, the head of the queue represented by |
428 |
|
|
* this deque (in other words, the first element of this deque). |
429 |
|
|
* This method differs from {@link #peek peek} only in that it throws an |
430 |
|
|
* exception if this deque is empty. |
431 |
|
|
* |
432 |
|
|
* <p>This method is equivalent to {@link #getFirst()}. |
433 |
|
|
* |
434 |
|
|
* @return the head of the queue represented by this deque |
435 |
|
|
* @throws NoSuchElementException if this deque is empty |
436 |
|
|
*/ |
437 |
|
|
E element(); |
438 |
|
|
|
439 |
|
|
/** |
440 |
|
|
* Retrieves, but does not remove, the head of the queue represented by |
441 |
|
|
* this deque (in other words, the first element of this deque), or |
442 |
|
|
* returns {@code null} if this deque is empty. |
443 |
|
|
* |
444 |
|
|
* <p>This method is equivalent to {@link #peekFirst()}. |
445 |
|
|
* |
446 |
|
|
* @return the head of the queue represented by this deque, or |
447 |
|
|
* {@code null} if this deque is empty |
448 |
|
|
*/ |
449 |
|
|
E peek(); |
450 |
|
|
|
451 |
|
|
|
452 |
|
|
// *** Stack methods *** |
453 |
|
|
|
454 |
|
|
/** |
455 |
|
|
* Pushes an element onto the stack represented by this deque (in other |
456 |
|
|
* words, at the head of this deque) if it is possible to do so |
457 |
|
|
* immediately without violating capacity restrictions, throwing an |
458 |
|
|
* {@code IllegalStateException} if no space is currently available. |
459 |
|
|
* |
460 |
|
|
* <p>This method is equivalent to {@link #addFirst}. |
461 |
|
|
* |
462 |
|
|
* @param e the element to push |
463 |
|
|
* @throws IllegalStateException if the element cannot be added at this |
464 |
|
|
* time due to capacity restrictions |
465 |
|
|
* @throws ClassCastException if the class of the specified element |
466 |
|
|
* prevents it from being added to this deque |
467 |
|
|
* @throws NullPointerException if the specified element is null and this |
468 |
|
|
* deque does not permit null elements |
469 |
|
|
* @throws IllegalArgumentException if some property of the specified |
470 |
|
|
* element prevents it from being added to this deque |
471 |
|
|
*/ |
472 |
|
|
void push(E e); |
473 |
|
|
|
474 |
|
|
/** |
475 |
|
|
* Pops an element from the stack represented by this deque. In other |
476 |
|
|
* words, removes and returns the first element of this deque. |
477 |
|
|
* |
478 |
|
|
* <p>This method is equivalent to {@link #removeFirst()}. |
479 |
|
|
* |
480 |
|
|
* @return the element at the front of this deque (which is the top |
481 |
|
|
* of the stack represented by this deque) |
482 |
|
|
* @throws NoSuchElementException if this deque is empty |
483 |
|
|
*/ |
484 |
|
|
E pop(); |
485 |
|
|
|
486 |
|
|
|
487 |
|
|
// *** Collection methods *** |
488 |
|
|
|
489 |
|
|
/** |
490 |
|
|
* Removes the first occurrence of the specified element from this deque. |
491 |
|
|
* If the deque does not contain the element, it is unchanged. |
492 |
|
|
* More formally, removes the first element {@code e} such that |
493 |
|
|
* {@code Objects.equals(o, e)} (if such an element exists). |
494 |
|
|
* Returns {@code true} if this deque contained the specified element |
495 |
|
|
* (or equivalently, if this deque changed as a result of the call). |
496 |
|
|
* |
497 |
|
|
* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
498 |
|
|
* |
499 |
|
|
* @param o element to be removed from this deque, if present |
500 |
|
|
* @return {@code true} if an element was removed as a result of this call |
501 |
|
|
* @throws ClassCastException if the class of the specified element |
502 |
|
|
* is incompatible with this deque |
503 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
504 |
|
|
* @throws NullPointerException if the specified element is null and this |
505 |
|
|
* deque does not permit null elements |
506 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
507 |
|
|
*/ |
508 |
|
|
boolean remove(Object o); |
509 |
|
|
|
510 |
|
|
/** |
511 |
|
|
* Returns {@code true} if this deque contains the specified element. |
512 |
|
|
* More formally, returns {@code true} if and only if this deque contains |
513 |
|
|
* at least one element {@code e} such that {@code Objects.equals(o, e)}. |
514 |
|
|
* |
515 |
|
|
* @param o element whose presence in this deque is to be tested |
516 |
|
|
* @return {@code true} if this deque contains the specified element |
517 |
|
|
* @throws ClassCastException if the class of the specified element |
518 |
|
|
* is incompatible with this deque |
519 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
520 |
|
|
* @throws NullPointerException if the specified element is null and this |
521 |
|
|
* deque does not permit null elements |
522 |
|
|
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
523 |
|
|
*/ |
524 |
|
|
boolean contains(Object o); |
525 |
|
|
|
526 |
|
|
/** |
527 |
|
|
* Returns the number of elements in this deque. |
528 |
|
|
* |
529 |
|
|
* @return the number of elements in this deque |
530 |
|
|
*/ |
531 |
|
|
int size(); |
532 |
|
|
|
533 |
|
|
/** |
534 |
|
|
* Returns an iterator over the elements in this deque in proper sequence. |
535 |
|
|
* The elements will be returned in order from first (head) to last (tail). |
536 |
|
|
* |
537 |
|
|
* @return an iterator over the elements in this deque in proper sequence |
538 |
|
|
*/ |
539 |
|
|
Iterator<E> iterator(); |
540 |
|
|
|
541 |
|
|
/** |
542 |
|
|
* Returns an iterator over the elements in this deque in reverse |
543 |
|
|
* sequential order. The elements will be returned in order from |
544 |
|
|
* last (tail) to first (head). |
545 |
|
|
* |
546 |
|
|
* @return an iterator over the elements in this deque in reverse |
547 |
|
|
* sequence |
548 |
|
|
*/ |
549 |
|
|
Iterator<E> descendingIterator(); |
550 |
|
|
|
551 |
|
|
} |