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1 : dl 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 : jsr166 1.20 * at http://creativecommons.org/publicdomain/zero/1.0/
5 : dl 1.1 */
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 <tt>Deque</tt>
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 <tt>null</tt> or <tt>false</tt>, depending on
22 :     * the operation). The latter form of the insert operation is
23 :     * designed specifically for use with capacity-restricted
24 :     * <tt>Deque</tt> implementations; in most implementations, insert
25 :     * operations cannot fail.
26 :     *
27 : dl 1.3 * <p>The twelve methods described above are summarized in the
28 : jsr166 1.5 * following table:
29 : dl 1.3 *
30 : jsr166 1.7 * <p>
31 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
32 : dl 1.1 * <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 : jsr166 1.8 * <td ALIGN=CENTER><em>Special value</em></td>
41 : dl 1.1 * <td ALIGN=CENTER><em>Throws exception</em></td>
42 : jsr166 1.8 * <td ALIGN=CENTER><em>Special value</em></td>
43 : dl 1.1 * </tr>
44 :     * <tr>
45 :     * <td><b>Insert</b></td>
46 :     * <td>{@link #addFirst addFirst(e)}</td>
47 :     * <td>{@link #offerFirst offerFirst(e)}</td>
48 :     * <td>{@link #addLast addLast(e)}</td>
49 :     * <td>{@link #offerLast offerLast(e)}</td>
50 :     * </tr>
51 :     * <tr>
52 :     * <td><b>Remove</b></td>
53 :     * <td>{@link #removeFirst removeFirst()}</td>
54 :     * <td>{@link #pollFirst pollFirst()}</td>
55 :     * <td>{@link #removeLast removeLast()}</td>
56 :     * <td>{@link #pollLast pollLast()}</td>
57 :     * </tr>
58 :     * <tr>
59 :     * <td><b>Examine</b></td>
60 :     * <td>{@link #getFirst getFirst()}</td>
61 :     * <td>{@link #peekFirst peekFirst()}</td>
62 :     * <td>{@link #getLast getLast()}</td>
63 :     * <td>{@link #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 : dl 1.4 * added at the end of the deque and removed from the beginning. The methods
70 : dl 1.1 * inherited from the <tt>Queue</tt> interface are precisely equivalent to
71 : jsr166 1.5 * <tt>Deque</tt> methods as indicated in the following table:
72 : dl 1.1 *
73 : jsr166 1.7 * <p>
74 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
75 : dl 1.1 * <tr>
76 :     * <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
77 :     * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
78 :     * </tr>
79 :     * <tr>
80 : jsr166 1.8 * <td>{@link java.util.Queue#add add(e)}</td>
81 :     * <td>{@link #addLast addLast(e)}</td>
82 :     * </tr>
83 :     * <tr>
84 : dl 1.1 * <td>{@link java.util.Queue#offer offer(e)}</td>
85 :     * <td>{@link #offerLast offerLast(e)}</td>
86 : jsr166 1.5 * </tr>
87 :     * <tr>
88 : jsr166 1.8 * <td>{@link java.util.Queue#remove remove()}</td>
89 :     * <td>{@link #removeFirst removeFirst()}</td>
90 : jsr166 1.5 * </tr>
91 :     * <tr>
92 : dl 1.1 * <td>{@link java.util.Queue#poll poll()}</td>
93 :     * <td>{@link #pollFirst pollFirst()}</td>
94 : jsr166 1.5 * </tr>
95 :     * <tr>
96 : jsr166 1.8 * <td>{@link java.util.Queue#element element()}</td>
97 :     * <td>{@link #getFirst getFirst()}</td>
98 : jsr166 1.5 * </tr>
99 :     * <tr>
100 : dl 1.1 * <td>{@link java.util.Queue#peek peek()}</td>
101 :     * <td>{@link #peek peekFirst()}</td>
102 : jsr166 1.5 * </tr>
103 : dl 1.1 * </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 : dl 1.3 * When a deque is used as a stack, elements are pushed and popped from the
108 : dl 1.1 * beginning of the deque. Stack methods are precisely equivalent to
109 : jsr166 1.5 * <tt>Deque</tt> methods as indicated in the table below:
110 : dl 1.1 *
111 : jsr166 1.7 * <p>
112 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
113 : dl 1.1 * <tr>
114 :     * <td ALIGN=CENTER> <b>Stack Method</b></td>
115 :     * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
116 :     * </tr>
117 :     * <tr>
118 :     * <td>{@link #push push(e)}</td>
119 :     * <td>{@link #addFirst addFirst(e)}</td>
120 : jsr166 1.5 * </tr>
121 :     * <tr>
122 : dl 1.1 * <td>{@link #pop pop()}</td>
123 :     * <td>{@link #removeFirst removeFirst()}</td>
124 : jsr166 1.5 * </tr>
125 :     * <tr>
126 : dl 1.1 * <td>{@link #peek peek()}</td>
127 :     * <td>{@link #peekFirst peekFirst()}</td>
128 : jsr166 1.5 * </tr>
129 : dl 1.1 * </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 : dl 1.2 * <p>This interface provides two methods to remove interior
136 : dl 1.1 * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
137 : jsr166 1.8 * {@link #removeLastOccurrence removeLastOccurrence}.
138 :     *
139 :     * <p>Unlike the {@link List} interface, this interface does not
140 :     * provide support for indexed access to elements.
141 : dl 1.1 *
142 :     * <p>While <tt>Deque</tt> 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
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
148 :     * to indicated that the deque is empty.
149 : dl 1.3 *
150 : dl 1.1 * <p><tt>Deque</tt> implementations generally do not define
151 :     * element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
152 :     * methods, but instead inherit the identity-based versions from class
153 :     * <tt>Object</tt>.
154 :     *
155 :     * <p>This interface is a member of the <a
156 : jsr166 1.19 * href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
157 : dl 1.1 * 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 collection
163 :     */
164 :     public interface Deque<E> extends Queue<E> {
165 :     /**
166 : jsr166 1.8 * Inserts the specified element at the front of this deque if it is
167 :     * possible to do so immediately without violating capacity restrictions.
168 :     * When using a capacity-restricted deque, it is generally preferable to
169 :     * use method {@link #offerFirst}.
170 :     *
171 :     * @param e the element to add
172 :     * @throws IllegalStateException if the element cannot be added at this
173 :     * time due to capacity restrictions
174 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
175 :     * prevents it from being added to this deque
176 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
177 :     * deque does not permit null elements
178 :     * @throws IllegalArgumentException if some property of the specified
179 :     * element prevents it from being added to this deque
180 :     */
181 :     void addFirst(E e);
182 :    
183 :     /**
184 : jsr166 1.13 * Inserts the specified element at the end of this deque if it is
185 : jsr166 1.8 * possible to do so immediately without violating capacity restrictions.
186 :     * When using a capacity-restricted deque, it is generally preferable to
187 :     * use method {@link #offerLast}.
188 :     *
189 : jsr166 1.14 * <p>This method is equivalent to {@link #add}.
190 :     *
191 : jsr166 1.8 * @param e the element to add
192 :     * @throws IllegalStateException if the element cannot be added at this
193 :     * time due to capacity restrictions
194 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
195 :     * prevents it from being added to this deque
196 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
197 :     * deque does not permit null elements
198 :     * @throws IllegalArgumentException if some property of the specified
199 :     * element prevents it from being added to this deque
200 :     */
201 :     void addLast(E e);
202 :    
203 :     /**
204 : dl 1.3 * Inserts the specified element at the front of this deque unless it would
205 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
206 : jsr166 1.8 * this method is generally preferable to the {@link #addFirst} method,
207 :     * which can fail to insert an element only by throwing an exception.
208 : dl 1.1 *
209 : jsr166 1.8 * @param e the element to add
210 : jsr166 1.11 * @return <tt>true</tt> if the element was added to this deque, else
211 :     * <tt>false</tt>
212 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
213 :     * prevents it from being added to this deque
214 : dl 1.3 * @throws NullPointerException if the specified element is null and this
215 : jsr166 1.8 * deque does not permit null elements
216 :     * @throws IllegalArgumentException if some property of the specified
217 :     * element prevents it from being added to this deque
218 : dl 1.1 */
219 :     boolean offerFirst(E e);
220 :    
221 :     /**
222 : dl 1.4 * Inserts the specified element at the end of this deque unless it would
223 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
224 : jsr166 1.8 * this method is generally preferable to the {@link #addLast} method,
225 :     * which can fail to insert an element only by throwing an exception.
226 : dl 1.1 *
227 : jsr166 1.8 * @param e the element to add
228 : jsr166 1.11 * @return <tt>true</tt> if the element was added to this deque, else
229 :     * <tt>false</tt>
230 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
231 :     * prevents it from being added to this deque
232 : dl 1.3 * @throws NullPointerException if the specified element is null and this
233 : jsr166 1.8 * deque does not permit null elements
234 :     * @throws IllegalArgumentException if some property of the specified
235 :     * element prevents it from being added to this deque
236 : dl 1.1 */
237 :     boolean offerLast(E e);
238 :    
239 :     /**
240 : jsr166 1.8 * Retrieves and removes the first element of this deque. This method
241 : jsr166 1.15 * differs from {@link #pollFirst pollFirst} only in that it throws an
242 :     * exception if this deque is empty.
243 : dl 1.1 *
244 : jsr166 1.8 * @return the head of this deque
245 :     * @throws NoSuchElementException if this deque is empty
246 : dl 1.1 */
247 : jsr166 1.8 E removeFirst();
248 : dl 1.1
249 :     /**
250 : jsr166 1.8 * Retrieves and removes the last element of this deque. This method
251 : jsr166 1.15 * differs from {@link #pollLast pollLast} only in that it throws an
252 :     * exception if this deque is empty.
253 : dl 1.1 *
254 : jsr166 1.8 * @return the tail of this deque
255 :     * @throws NoSuchElementException if this deque is empty
256 : dl 1.1 */
257 : jsr166 1.8 E removeLast();
258 : dl 1.1
259 :     /**
260 : jsr166 1.8 * Retrieves and removes the first element of this deque,
261 :     * or returns <tt>null</tt> if this deque is empty.
262 : dl 1.1 *
263 : jsr166 1.8 * @return the head of this deque, or <tt>null</tt> if this deque is empty
264 : dl 1.1 */
265 :     E pollFirst();
266 :    
267 :     /**
268 : jsr166 1.8 * Retrieves and removes the last element of this deque,
269 :     * or returns <tt>null</tt> if this deque is empty.
270 : dl 1.1 *
271 : jsr166 1.8 * @return the tail of this deque, or <tt>null</tt> if this deque is empty
272 : dl 1.1 */
273 :     E pollLast();
274 :    
275 :     /**
276 : jsr166 1.8 * Retrieves, but does not remove, the first element of this deque.
277 : jsr166 1.16 *
278 : jsr166 1.15 * This method differs from {@link #peekFirst peekFirst} only in that it
279 :     * throws an exception if this deque is empty.
280 : dl 1.1 *
281 : jsr166 1.8 * @return the head of this deque
282 : dl 1.1 * @throws NoSuchElementException if this deque is empty
283 :     */
284 : jsr166 1.8 E getFirst();
285 : dl 1.1
286 :     /**
287 : jsr166 1.8 * Retrieves, but does not remove, the last element of this deque.
288 : jsr166 1.15 * This method differs from {@link #peekLast peekLast} only in that it
289 :     * throws an exception if this deque is empty.
290 : dl 1.1 *
291 : jsr166 1.8 * @return the tail of this deque
292 : dl 1.1 * @throws NoSuchElementException if this deque is empty
293 :     */
294 : jsr166 1.8 E getLast();
295 : dl 1.1
296 :     /**
297 :     * Retrieves, but does not remove, the first element of this deque,
298 : jsr166 1.8 * or returns <tt>null</tt> if this deque is empty.
299 : dl 1.1 *
300 : jsr166 1.8 * @return the head of this deque, or <tt>null</tt> if this deque is empty
301 : dl 1.1 */
302 :     E peekFirst();
303 :    
304 :     /**
305 :     * Retrieves, but does not remove, the last element of this deque,
306 : jsr166 1.8 * or returns <tt>null</tt> if this deque is empty.
307 : dl 1.1 *
308 : jsr166 1.8 * @return the tail of this deque, or <tt>null</tt> if this deque is empty
309 : dl 1.1 */
310 :     E peekLast();
311 :    
312 :     /**
313 : jsr166 1.8 * 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
316 : jsr166 1.9 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>
317 :     * (if such an element exists).
318 : jsr166 1.12 * Returns <tt>true</tt> if this deque contained the specified element
319 :     * (or equivalently, if this deque changed as a result of the call).
320 : dl 1.1 *
321 : dl 1.3 * @param o element to be removed from this deque, if present
322 : jsr166 1.8 * @return <tt>true</tt> if an element was removed as a result of this call
323 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
324 :     * is incompatible with this deque (optional)
325 : dl 1.4 * @throws NullPointerException if the specified element is null and this
326 : jsr166 1.8 * deque does not permit null elements (optional)
327 : dl 1.1 */
328 : dl 1.3 boolean removeFirstOccurrence(Object o);
329 : dl 1.1
330 :     /**
331 : jsr166 1.8 * 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
334 : jsr166 1.9 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>
335 :     * (if such an element exists).
336 : jsr166 1.12 * Returns <tt>true</tt> if this deque contained the specified element
337 :     * (or equivalently, if this deque changed as a result of the call).
338 : dl 1.1 *
339 : dl 1.3 * @param o element to be removed from this deque, if present
340 : jsr166 1.8 * @return <tt>true</tt> if an element was removed as a result of this call
341 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
342 :     * is incompatible with this deque (optional)
343 : dl 1.4 * @throws NullPointerException if the specified element is null and this
344 : jsr166 1.8 * deque does not permit null elements (optional)
345 : dl 1.1 */
346 : dl 1.3 boolean removeLastOccurrence(Object o);
347 : dl 1.1
348 : jsr166 1.8 // *** Queue methods ***
349 : dl 1.1
350 : jsr166 1.8 /**
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.
356 :     * When using a capacity-restricted deque, it is generally preferable to
357 :     * use {@link #offer(Object) offer}.
358 :     *
359 : jsr166 1.14 * <p>This method is equivalent to {@link #addLast}.
360 : jsr166 1.8 *
361 :     * @param e the element to add
362 : jsr166 1.15 * @return <tt>true</tt> (as specified by {@link Collection#add})
363 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
364 :     * time due to capacity restrictions
365 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
366 :     * prevents it from being added to this deque
367 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
368 :     * deque does not permit null elements
369 :     * @throws IllegalArgumentException if some property of the specified
370 :     * element prevents it from being added to this deque
371 :     */
372 :     boolean add(E e);
373 : dl 1.1
374 :     /**
375 :     * Inserts the specified element into the queue represented by this deque
376 : jsr166 1.8 * (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
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.
382 : dl 1.1 *
383 :     * <p>This method is equivalent to {@link #offerLast}.
384 :     *
385 : jsr166 1.8 * @param e the element to add
386 :     * @return <tt>true</tt> if the element was added to this deque, else
387 :     * <tt>false</tt>
388 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
389 :     * prevents it from being added to this deque
390 : dl 1.3 * @throws NullPointerException if the specified element is null and this
391 : jsr166 1.8 * deque does not permit null elements
392 :     * @throws IllegalArgumentException if some property of the specified
393 :     * element prevents it from being added to this deque
394 : dl 1.1 */
395 :     boolean offer(E e);
396 :    
397 :     /**
398 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
399 :     * (in other words, the first element of this deque).
400 : jsr166 1.15 * This method differs from {@link #poll poll} only in that it throws an
401 : jsr166 1.8 * exception if this deque is empty.
402 : dl 1.1 *
403 : jsr166 1.8 * <p>This method is equivalent to {@link #removeFirst()}.
404 : dl 1.1 *
405 : jsr166 1.8 * @return the head of the queue represented by this deque
406 :     * @throws NoSuchElementException if this deque is empty
407 : dl 1.1 */
408 : jsr166 1.8 E remove();
409 : dl 1.1
410 :     /**
411 : jsr166 1.8 * 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.
414 : dl 1.1 *
415 :     * <p>This method is equivalent to {@link #pollFirst()}.
416 :     *
417 :     * @return the first element of this deque, or <tt>null</tt> if
418 : jsr166 1.8 * this deque is empty
419 : dl 1.1 */
420 :     E poll();
421 :    
422 :     /**
423 : jsr166 1.8 * Retrieves, but does not remove, the head of the queue represented by
424 :     * this deque (in other words, the first element of this deque).
425 : jsr166 1.15 * This method differs from {@link #peek peek} only in that it throws an
426 : jsr166 1.8 * exception if this deque is empty.
427 : dl 1.1 *
428 : jsr166 1.8 * <p>This method is equivalent to {@link #getFirst()}.
429 : dl 1.1 *
430 :     * @return the head of the queue represented by this deque
431 :     * @throws NoSuchElementException if this deque is empty
432 :     */
433 : jsr166 1.8 E element();
434 : dl 1.1
435 :     /**
436 :     * Retrieves, but does not remove, the head of the queue represented by
437 : jsr166 1.8 * this deque (in other words, the first element of this deque), or
438 :     * returns <tt>null</tt> if this deque is empty.
439 : dl 1.1 *
440 : dl 1.3 * <p>This method is equivalent to {@link #peekFirst()}.
441 : dl 1.1 *
442 :     * @return the head of the queue represented by this deque, or
443 : jsr166 1.8 * <tt>null</tt> if this deque is empty
444 : dl 1.1 */
445 :     E peek();
446 :    
447 :    
448 :     // *** Stack methods ***
449 :    
450 :     /**
451 : jsr166 1.8 * 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.
456 : dl 1.1 *
457 :     * <p>This method is equivalent to {@link #addFirst}.
458 :     *
459 : dl 1.3 * @param e the element to push
460 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
461 :     * time due to capacity restrictions
462 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
463 :     * prevents it from being added to this deque
464 : dl 1.3 * @throws NullPointerException if the specified element is null and this
465 : jsr166 1.8 * deque does not permit null elements
466 :     * @throws IllegalArgumentException if some property of the specified
467 :     * element prevents it from being added to this deque
468 : dl 1.1 */
469 :     void push(E e);
470 :    
471 :     /**
472 :     * Pops an element from the stack represented by this deque. In other
473 : dl 1.2 * words, removes and returns the first element of this deque.
474 : dl 1.1 *
475 :     * <p>This method is equivalent to {@link #removeFirst()}.
476 :     *
477 :     * @return the element at the front of this deque (which is the top
478 : jsr166 1.8 * of the stack represented by this deque)
479 : dl 1.1 * @throws NoSuchElementException if this deque is empty
480 :     */
481 :     E pop();
482 :    
483 :    
484 : jsr166 1.8 // *** Collection methods ***
485 :    
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
490 : jsr166 1.9 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>
491 :     * (if such an element exists).
492 : jsr166 1.12 * Returns <tt>true</tt> if this deque contained the specified element
493 :     * (or equivalently, if this deque changed as a result of the call).
494 : jsr166 1.8 *
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
499 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
500 :     * is incompatible with this deque (optional)
501 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
502 :     * deque does not permit null elements (optional)
503 :     */
504 :     boolean remove(Object o);
505 :    
506 :     /**
507 :     * Returns <tt>true</tt> if this deque contains the specified element.
508 : jsr166 1.9 * More formally, returns <tt>true</tt> if and only if this deque contains
509 :     * at least one element <tt>e</tt> such that
510 :     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
511 : jsr166 1.8 *
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
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
517 :     * deque does not permit null elements (optional)
518 :     */
519 :     boolean contains(Object o);
520 :    
521 :     /**
522 :     * Returns the number of elements in this deque.
523 :     *
524 :     * @return the number of elements in this deque
525 :     */
526 :     public int size();
527 : dl 1.1
528 :     /**
529 : jsr166 1.10 * Returns an iterator over the elements in this deque in proper sequence.
530 :     * The elements will be returned in order from first (head) to last (tail).
531 : dl 1.3 *
532 : jsr166 1.10 * @return an iterator over the elements in this deque in proper sequence
533 : dl 1.1 */
534 :     Iterator<E> iterator();
535 : dl 1.17
536 :     /**
537 :     * Returns an iterator over the elements in this deque in reverse
538 :     * sequential order. The elements will be returned in order from
539 :     * last (tail) to first (head).
540 :     *
541 :     * @return an iterator over the elements in this deque in reverse
542 :     * sequence
543 :     */
544 :     Iterator<E> descendingIterator();
545 :    
546 : dl 1.1 }

Doug Lea
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