9 |
|
/** |
10 |
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* 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 <tt>Deque</tt> |
12 |
> |
* and is usually pronounced "deck". Most {@code Deque} |
13 |
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* implementations place no fixed limits on the number of elements |
14 |
|
* they may contain, but this interface supports capacity-restricted |
15 |
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* deques as well as those with no fixed size limit. |
18 |
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* ends of the deque. Methods are provided to insert, remove, and |
19 |
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* examine the element. Each of these methods exists in two forms: |
20 |
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* one throws an exception if the operation fails, the other returns a |
21 |
< |
* special value (either <tt>null</tt> or <tt>false</tt>, depending on |
21 |
> |
* special value (either {@code null} or {@code false}, depending on |
22 |
|
* the operation). The latter form of the insert operation is |
23 |
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* designed specifically for use with capacity-restricted |
24 |
< |
* <tt>Deque</tt> implementations; in most implementations, insert |
24 |
> |
* {@code Deque} implementations; in most implementations, insert |
25 |
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* operations cannot fail. |
26 |
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* |
27 |
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* <p>The twelve methods described above are summarized in the |
67 |
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* <p>This interface extends the {@link Queue} interface. When a deque is |
68 |
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* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are |
69 |
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* added at the end of the deque and removed from the beginning. The methods |
70 |
< |
* inherited from the <tt>Queue</tt> interface are precisely equivalent to |
71 |
< |
* <tt>Deque</tt> methods as indicated in the following table: |
70 |
> |
* inherited from the {@code Queue} interface are precisely equivalent to |
71 |
> |
* {@code Deque} methods as indicated in the following table: |
72 |
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* |
73 |
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* <p> |
74 |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
75 |
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* <tr> |
76 |
< |
* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td> |
77 |
< |
* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> |
76 |
> |
* <td ALIGN=CENTER> <b>{@code Queue} Method</b></td> |
77 |
> |
* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
78 |
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* </tr> |
79 |
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* <tr> |
80 |
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* <td>{@link java.util.Queue#add add(e)}</td> |
106 |
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* interface should be used in preference to the legacy {@link Stack} class. |
107 |
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* When a deque is used as a stack, elements are pushed and popped from the |
108 |
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* beginning of the deque. Stack methods are precisely equivalent to |
109 |
< |
* <tt>Deque</tt> methods as indicated in the table below: |
109 |
> |
* {@code Deque} methods as indicated in the table below: |
110 |
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* |
111 |
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* <p> |
112 |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
113 |
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* <tr> |
114 |
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* <td ALIGN=CENTER> <b>Stack Method</b></td> |
115 |
< |
* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> |
115 |
> |
* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
116 |
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* </tr> |
117 |
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* <tr> |
118 |
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* <td>{@link #push push(e)}</td> |
139 |
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* <p>Unlike the {@link List} interface, this interface does not |
140 |
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* provide support for indexed access to elements. |
141 |
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* |
142 |
< |
* <p>While <tt>Deque</tt> implementations are not strictly required |
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 <tt>Deque</tt> implementations |
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 |
< |
* <tt>null</tt> is used as a special return value by various methods |
147 |
> |
* {@code null} is used as a special return value by various methods |
148 |
|
* to indicated that the deque is empty. |
149 |
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* |
150 |
< |
* <p><tt>Deque</tt> implementations generally do not define |
151 |
< |
* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt> |
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 |
< |
* <tt>Object</tt>. |
153 |
> |
* {@code Object}. |
154 |
|
* |
155 |
|
* <p>This interface is a member of the <a |
156 |
|
* href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections |
207 |
|
* which can fail to insert an element only by throwing an exception. |
208 |
|
* |
209 |
|
* @param e the element to add |
210 |
< |
* @return <tt>true</tt> if the element was added to this deque, else |
211 |
< |
* <tt>false</tt> |
210 |
> |
* @return {@code true} if the element was added to this deque, else |
211 |
> |
* {@code false} |
212 |
|
* @throws ClassCastException if the class of the specified element |
213 |
|
* prevents it from being added to this deque |
214 |
|
* @throws NullPointerException if the specified element is null and this |
225 |
|
* which can fail to insert an element only by throwing an exception. |
226 |
|
* |
227 |
|
* @param e the element to add |
228 |
< |
* @return <tt>true</tt> if the element was added to this deque, else |
229 |
< |
* <tt>false</tt> |
228 |
> |
* @return {@code true} if the element was added to this deque, else |
229 |
> |
* {@code false} |
230 |
|
* @throws ClassCastException if the class of the specified element |
231 |
|
* prevents it from being added to this deque |
232 |
|
* @throws NullPointerException if the specified element is null and this |
258 |
|
|
259 |
|
/** |
260 |
|
* Retrieves and removes the first element of this deque, |
261 |
< |
* or returns <tt>null</tt> if this deque is empty. |
261 |
> |
* or returns {@code null} if this deque is empty. |
262 |
|
* |
263 |
< |
* @return the head of this deque, or <tt>null</tt> if this deque is empty |
263 |
> |
* @return the head of this deque, or {@code null} if this deque is empty |
264 |
|
*/ |
265 |
|
E pollFirst(); |
266 |
|
|
267 |
|
/** |
268 |
|
* Retrieves and removes the last element of this deque, |
269 |
< |
* or returns <tt>null</tt> if this deque is empty. |
269 |
> |
* or returns {@code null} if this deque is empty. |
270 |
|
* |
271 |
< |
* @return the tail of this deque, or <tt>null</tt> if this deque is empty |
271 |
> |
* @return the tail of this deque, or {@code null} if this deque is empty |
272 |
|
*/ |
273 |
|
E pollLast(); |
274 |
|
|
295 |
|
|
296 |
|
/** |
297 |
|
* Retrieves, but does not remove, the first element of this deque, |
298 |
< |
* or returns <tt>null</tt> if this deque is empty. |
298 |
> |
* or returns {@code null} if this deque is empty. |
299 |
|
* |
300 |
< |
* @return the head of this deque, or <tt>null</tt> if this deque is empty |
300 |
> |
* @return the head of this deque, or {@code null} if this deque is empty |
301 |
|
*/ |
302 |
|
E peekFirst(); |
303 |
|
|
304 |
|
/** |
305 |
|
* Retrieves, but does not remove, the last element of this deque, |
306 |
< |
* or returns <tt>null</tt> if this deque is empty. |
306 |
> |
* or returns {@code null} if this deque is empty. |
307 |
|
* |
308 |
< |
* @return the tail of this deque, or <tt>null</tt> if this deque is empty |
308 |
> |
* @return the tail of this deque, or {@code null} if this deque is empty |
309 |
|
*/ |
310 |
|
E peekLast(); |
311 |
|
|
312 |
|
/** |
313 |
|
* Removes the first occurrence of the specified element from this deque. |
314 |
|
* If the deque does not contain the element, it is unchanged. |
315 |
< |
* More formally, removes the first element <tt>e</tt> such that |
315 |
> |
* More formally, removes the first element {@code e} such that |
316 |
|
* <tt>(o==null ? e==null : o.equals(e))</tt> |
317 |
|
* (if such an element exists). |
318 |
< |
* Returns <tt>true</tt> if this deque contained the specified element |
318 |
> |
* Returns {@code true} if this deque contained the specified element |
319 |
|
* (or equivalently, if this deque changed as a result of the call). |
320 |
|
* |
321 |
|
* @param o element to be removed from this deque, if present |
322 |
< |
* @return <tt>true</tt> if an element was removed as a result of this call |
322 |
> |
* @return {@code true} if an element was removed as a result of this call |
323 |
|
* @throws ClassCastException if the class of the specified element |
324 |
|
* is incompatible with this deque (optional) |
325 |
|
* @throws NullPointerException if the specified element is null and this |
330 |
|
/** |
331 |
|
* Removes the last occurrence of the specified element from this deque. |
332 |
|
* If the deque does not contain the element, it is unchanged. |
333 |
< |
* More formally, removes the last element <tt>e</tt> such that |
333 |
> |
* More formally, removes the last element {@code e} such that |
334 |
|
* <tt>(o==null ? e==null : o.equals(e))</tt> |
335 |
|
* (if such an element exists). |
336 |
< |
* Returns <tt>true</tt> if this deque contained the specified element |
336 |
> |
* Returns {@code true} if this deque contained the specified element |
337 |
|
* (or equivalently, if this deque changed as a result of the call). |
338 |
|
* |
339 |
|
* @param o element to be removed from this deque, if present |
340 |
< |
* @return <tt>true</tt> if an element was removed as a result of this call |
340 |
> |
* @return {@code true} if an element was removed as a result of this call |
341 |
|
* @throws ClassCastException if the class of the specified element |
342 |
|
* is incompatible with this deque (optional) |
343 |
|
* @throws NullPointerException if the specified element is null and this |
351 |
|
* Inserts the specified element into the queue represented by this deque |
352 |
|
* (in other words, at the tail of this deque) if it is possible to do so |
353 |
|
* immediately without violating capacity restrictions, returning |
354 |
< |
* <tt>true</tt> upon success and throwing an |
355 |
< |
* <tt>IllegalStateException</tt> if no space is currently available. |
354 |
> |
* {@code true} upon success and throwing an |
355 |
> |
* {@code IllegalStateException} if no space is currently available. |
356 |
|
* When using a capacity-restricted deque, it is generally preferable to |
357 |
|
* use {@link #offer(Object) offer}. |
358 |
|
* |
359 |
|
* <p>This method is equivalent to {@link #addLast}. |
360 |
|
* |
361 |
|
* @param e the element to add |
362 |
< |
* @return <tt>true</tt> (as specified by {@link Collection#add}) |
362 |
> |
* @return {@code true} (as specified by {@link Collection#add}) |
363 |
|
* @throws IllegalStateException if the element cannot be added at this |
364 |
|
* time due to capacity restrictions |
365 |
|
* @throws ClassCastException if the class of the specified element |
375 |
|
* Inserts the specified element into the queue represented by this deque |
376 |
|
* (in other words, at the tail of this deque) if it is possible to do so |
377 |
|
* immediately without violating capacity restrictions, returning |
378 |
< |
* <tt>true</tt> upon success and <tt>false</tt> if no space is currently |
378 |
> |
* {@code true} upon success and {@code false} if no space is currently |
379 |
|
* available. When using a capacity-restricted deque, this method is |
380 |
|
* generally preferable to the {@link #add} method, which can fail to |
381 |
|
* insert an element only by throwing an exception. |
383 |
|
* <p>This method is equivalent to {@link #offerLast}. |
384 |
|
* |
385 |
|
* @param e the element to add |
386 |
< |
* @return <tt>true</tt> if the element was added to this deque, else |
387 |
< |
* <tt>false</tt> |
386 |
> |
* @return {@code true} if the element was added to this deque, else |
387 |
> |
* {@code false} |
388 |
|
* @throws ClassCastException if the class of the specified element |
389 |
|
* prevents it from being added to this deque |
390 |
|
* @throws NullPointerException if the specified element is null and this |
410 |
|
/** |
411 |
|
* Retrieves and removes the head of the queue represented by this deque |
412 |
|
* (in other words, the first element of this deque), or returns |
413 |
< |
* <tt>null</tt> if this deque is empty. |
413 |
> |
* {@code null} if this deque is empty. |
414 |
|
* |
415 |
|
* <p>This method is equivalent to {@link #pollFirst()}. |
416 |
|
* |
417 |
< |
* @return the first element of this deque, or <tt>null</tt> if |
417 |
> |
* @return the first element of this deque, or {@code null} if |
418 |
|
* this deque is empty |
419 |
|
*/ |
420 |
|
E poll(); |
435 |
|
/** |
436 |
|
* Retrieves, but does not remove, the head of the queue represented by |
437 |
|
* this deque (in other words, the first element of this deque), or |
438 |
< |
* returns <tt>null</tt> if this deque is empty. |
438 |
> |
* returns {@code null} if this deque is empty. |
439 |
|
* |
440 |
|
* <p>This method is equivalent to {@link #peekFirst()}. |
441 |
|
* |
442 |
|
* @return the head of the queue represented by this deque, or |
443 |
< |
* <tt>null</tt> if this deque is empty |
443 |
> |
* {@code null} if this deque is empty |
444 |
|
*/ |
445 |
|
E peek(); |
446 |
|
|
451 |
|
* Pushes an element onto the stack represented by this deque (in other |
452 |
|
* words, at the head of this deque) if it is possible to do so |
453 |
|
* immediately without violating capacity restrictions, returning |
454 |
< |
* <tt>true</tt> upon success and throwing an |
455 |
< |
* <tt>IllegalStateException</tt> if no space is currently available. |
454 |
> |
* {@code true} upon success and throwing an |
455 |
> |
* {@code IllegalStateException} if no space is currently available. |
456 |
|
* |
457 |
|
* <p>This method is equivalent to {@link #addFirst}. |
458 |
|
* |
486 |
|
/** |
487 |
|
* Removes the first occurrence of the specified element from this deque. |
488 |
|
* If the deque does not contain the element, it is unchanged. |
489 |
< |
* More formally, removes the first element <tt>e</tt> such that |
489 |
> |
* More formally, removes the first element {@code e} such that |
490 |
|
* <tt>(o==null ? e==null : o.equals(e))</tt> |
491 |
|
* (if such an element exists). |
492 |
< |
* Returns <tt>true</tt> if this deque contained the specified element |
492 |
> |
* Returns {@code true} if this deque contained the specified element |
493 |
|
* (or equivalently, if this deque changed as a result of the call). |
494 |
|
* |
495 |
|
* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
496 |
|
* |
497 |
|
* @param o element to be removed from this deque, if present |
498 |
< |
* @return <tt>true</tt> if an element was removed as a result of this call |
498 |
> |
* @return {@code true} if an element was removed as a result of this call |
499 |
|
* @throws ClassCastException if the class of the specified element |
500 |
|
* is incompatible with this deque (optional) |
501 |
|
* @throws NullPointerException if the specified element is null and this |
504 |
|
boolean remove(Object o); |
505 |
|
|
506 |
|
/** |
507 |
< |
* Returns <tt>true</tt> if this deque contains the specified element. |
508 |
< |
* More formally, returns <tt>true</tt> if and only if this deque contains |
509 |
< |
* at least one element <tt>e</tt> such that |
507 |
> |
* Returns {@code true} if this deque contains the specified element. |
508 |
> |
* More formally, returns {@code true} if and only if this deque contains |
509 |
> |
* at least one element {@code e} such that |
510 |
|
* <tt>(o==null ? e==null : o.equals(e))</tt>. |
511 |
|
* |
512 |
|
* @param o element whose presence in this deque is to be tested |
513 |
< |
* @return <tt>true</tt> if this deque contains the specified element |
513 |
> |
* @return {@code true} if this deque contains the specified element |
514 |
|
* @throws ClassCastException if the type of the specified element |
515 |
|
* is incompatible with this deque (optional) |
516 |
|
* @throws NullPointerException if the specified element is null and this |