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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 :     * at http://creativecommons.org/licenses/publicdomain
5 :     */
6 :    
7 :     package java.util;
8 : jsr166 1.15 import java.util.*; // for javadoc (till 6280605 is fixed)
9 : dl 1.1
10 :     /**
11 :     * A linear collection that supports element insertion and removal at
12 :     * both ends. The name <i>deque</i> is short for "double ended queue"
13 :     * and is usually pronounced "deck". Most <tt>Deque</tt>
14 :     * implementations place no fixed limits on the number of elements
15 :     * they may contain, but this interface supports capacity-restricted
16 :     * deques as well as those with no fixed size limit.
17 :     *
18 :     * <p>This interface defines methods to access the elements at both
19 :     * ends of the deque. Methods are provided to insert, remove, and
20 :     * examine the element. Each of these methods exists in two forms:
21 :     * one throws an exception if the operation fails, the other returns a
22 :     * special value (either <tt>null</tt> or <tt>false</tt>, depending on
23 :     * the operation). The latter form of the insert operation is
24 :     * designed specifically for use with capacity-restricted
25 :     * <tt>Deque</tt> implementations; in most implementations, insert
26 :     * operations cannot fail.
27 :     *
28 : dl 1.3 * <p>The twelve methods described above are summarized in the
29 : jsr166 1.5 * following table:
30 : dl 1.3 *
31 : jsr166 1.7 * <p>
32 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
33 : dl 1.1 * <tr>
34 :     * <td></td>
35 :     * <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
36 :     * <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
37 :     * </tr>
38 :     * <tr>
39 :     * <td></td>
40 :     * <td ALIGN=CENTER><em>Throws exception</em></td>
41 : jsr166 1.8 * <td ALIGN=CENTER><em>Special value</em></td>
42 : dl 1.1 * <td ALIGN=CENTER><em>Throws exception</em></td>
43 : jsr166 1.8 * <td ALIGN=CENTER><em>Special value</em></td>
44 : dl 1.1 * </tr>
45 :     * <tr>
46 :     * <td><b>Insert</b></td>
47 :     * <td>{@link #addFirst addFirst(e)}</td>
48 :     * <td>{@link #offerFirst offerFirst(e)}</td>
49 :     * <td>{@link #addLast addLast(e)}</td>
50 :     * <td>{@link #offerLast offerLast(e)}</td>
51 :     * </tr>
52 :     * <tr>
53 :     * <td><b>Remove</b></td>
54 :     * <td>{@link #removeFirst removeFirst()}</td>
55 :     * <td>{@link #pollFirst pollFirst()}</td>
56 :     * <td>{@link #removeLast removeLast()}</td>
57 :     * <td>{@link #pollLast pollLast()}</td>
58 :     * </tr>
59 :     * <tr>
60 :     * <td><b>Examine</b></td>
61 :     * <td>{@link #getFirst getFirst()}</td>
62 :     * <td>{@link #peekFirst peekFirst()}</td>
63 :     * <td>{@link #getLast getLast()}</td>
64 :     * <td>{@link #peekLast peekLast()}</td>
65 :     * </tr>
66 :     * </table>
67 :     *
68 :     * <p>This interface extends the {@link Queue} interface. When a deque is
69 :     * used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
70 : dl 1.4 * added at the end of the deque and removed from the beginning. The methods
71 : dl 1.1 * inherited from the <tt>Queue</tt> interface are precisely equivalent to
72 : jsr166 1.5 * <tt>Deque</tt> methods as indicated in the following table:
73 : dl 1.1 *
74 : jsr166 1.7 * <p>
75 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
76 : dl 1.1 * <tr>
77 :     * <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
78 :     * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
79 :     * </tr>
80 :     * <tr>
81 : jsr166 1.8 * <td>{@link java.util.Queue#add add(e)}</td>
82 :     * <td>{@link #addLast addLast(e)}</td>
83 :     * </tr>
84 :     * <tr>
85 : dl 1.1 * <td>{@link java.util.Queue#offer offer(e)}</td>
86 :     * <td>{@link #offerLast offerLast(e)}</td>
87 : jsr166 1.5 * </tr>
88 :     * <tr>
89 : jsr166 1.8 * <td>{@link java.util.Queue#remove remove()}</td>
90 :     * <td>{@link #removeFirst removeFirst()}</td>
91 : jsr166 1.5 * </tr>
92 :     * <tr>
93 : dl 1.1 * <td>{@link java.util.Queue#poll poll()}</td>
94 :     * <td>{@link #pollFirst pollFirst()}</td>
95 : jsr166 1.5 * </tr>
96 :     * <tr>
97 : jsr166 1.8 * <td>{@link java.util.Queue#element element()}</td>
98 :     * <td>{@link #getFirst getFirst()}</td>
99 : jsr166 1.5 * </tr>
100 :     * <tr>
101 : dl 1.1 * <td>{@link java.util.Queue#peek peek()}</td>
102 :     * <td>{@link #peek peekFirst()}</td>
103 : jsr166 1.5 * </tr>
104 : dl 1.1 * </table>
105 :     *
106 :     * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
107 :     * interface should be used in preference to the legacy {@link Stack} class.
108 : dl 1.3 * When a deque is used as a stack, elements are pushed and popped from the
109 : dl 1.1 * beginning of the deque. Stack methods are precisely equivalent to
110 : jsr166 1.5 * <tt>Deque</tt> methods as indicated in the table below:
111 : dl 1.1 *
112 : jsr166 1.7 * <p>
113 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
114 : dl 1.1 * <tr>
115 :     * <td ALIGN=CENTER> <b>Stack Method</b></td>
116 :     * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
117 :     * </tr>
118 :     * <tr>
119 :     * <td>{@link #push push(e)}</td>
120 :     * <td>{@link #addFirst addFirst(e)}</td>
121 : jsr166 1.5 * </tr>
122 :     * <tr>
123 : dl 1.1 * <td>{@link #pop pop()}</td>
124 :     * <td>{@link #removeFirst removeFirst()}</td>
125 : jsr166 1.5 * </tr>
126 :     * <tr>
127 : dl 1.1 * <td>{@link #peek peek()}</td>
128 :     * <td>{@link #peekFirst peekFirst()}</td>
129 : jsr166 1.5 * </tr>
130 : dl 1.1 * </table>
131 :     *
132 :     * <p>Note that the {@link #peek peek} method works equally well when
133 :     * a deque is used as a queue or a stack; in either case, elements are
134 :     * drawn from the beginning of the deque.
135 :     *
136 : dl 1.2 * <p>This interface provides two methods to remove interior
137 : dl 1.1 * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
138 : jsr166 1.8 * {@link #removeLastOccurrence removeLastOccurrence}.
139 :     *
140 :     * <p>Unlike the {@link List} interface, this interface does not
141 :     * provide support for indexed access to elements.
142 : dl 1.1 *
143 :     * <p>While <tt>Deque</tt> implementations are not strictly required
144 :     * to prohibit the insertion of null elements, they are strongly
145 :     * encouraged to do so. Users of any <tt>Deque</tt> implementations
146 :     * that do allow null elements are strongly encouraged <i>not</i> to
147 :     * take advantage of the ability to insert nulls. This is so because
148 :     * <tt>null</tt> is used as a special return value by various methods
149 :     * to indicated that the deque is empty.
150 : dl 1.3 *
151 : dl 1.1 * <p><tt>Deque</tt> implementations generally do not define
152 :     * element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
153 :     * methods, but instead inherit the identity-based versions from class
154 :     * <tt>Object</tt>.
155 :     *
156 :     * <p>This interface is a member of the <a
157 :     * href="{@docRoot}/../guide/collections/index.html"> Java Collections
158 :     * Framework</a>.
159 :     *
160 :     * @author Doug Lea
161 :     * @author Josh Bloch
162 :     * @since 1.6
163 :     * @param <E> the type of elements held in this collection
164 :     */
165 :    
166 :     public interface Deque<E> extends Queue<E> {
167 :     /**
168 : jsr166 1.8 * Inserts the specified element at the front of this deque if it is
169 :     * possible to do so immediately without violating capacity restrictions.
170 :     * When using a capacity-restricted deque, it is generally preferable to
171 :     * use method {@link #offerFirst}.
172 :     *
173 :     * @param e the element to add
174 :     * @throws IllegalStateException if the element cannot be added at this
175 :     * time due to capacity restrictions
176 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
177 :     * prevents it from being added to this deque
178 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
179 :     * deque does not permit null elements
180 :     * @throws IllegalArgumentException if some property of the specified
181 :     * element prevents it from being added to this deque
182 :     */
183 :     void addFirst(E e);
184 :    
185 :     /**
186 : jsr166 1.13 * Inserts the specified element at the end of this deque if it is
187 : jsr166 1.8 * possible to do so immediately without violating capacity restrictions.
188 :     * When using a capacity-restricted deque, it is generally preferable to
189 :     * use method {@link #offerLast}.
190 :     *
191 : jsr166 1.14 * <p>This method is equivalent to {@link #add}.
192 :     *
193 : jsr166 1.8 * @param e the element to add
194 :     * @throws IllegalStateException if the element cannot be added at this
195 :     * time due to capacity restrictions
196 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
197 :     * prevents it from being added to this deque
198 : jsr166 1.8 * @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 : dl 1.3 * Inserts the specified element at the front of this deque unless it would
207 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
208 : jsr166 1.8 * this method is generally preferable to the {@link #addFirst} method,
209 :     * which can fail to insert an element only by throwing an exception.
210 : dl 1.1 *
211 : jsr166 1.8 * @param e the element to add
212 : jsr166 1.11 * @return <tt>true</tt> if the element was added to this deque, else
213 :     * <tt>false</tt>
214 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
215 :     * prevents it from being added to this deque
216 : dl 1.3 * @throws NullPointerException if the specified element is null and this
217 : jsr166 1.8 * 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 : dl 1.1 */
221 :     boolean offerFirst(E e);
222 :    
223 :     /**
224 : dl 1.4 * Inserts the specified element at the end of this deque unless it would
225 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
226 : jsr166 1.8 * this method is generally preferable to the {@link #addLast} method,
227 :     * which can fail to insert an element only by throwing an exception.
228 : dl 1.1 *
229 : jsr166 1.8 * @param e the element to add
230 : jsr166 1.11 * @return <tt>true</tt> if the element was added to this deque, else
231 :     * <tt>false</tt>
232 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
233 :     * prevents it from being added to this deque
234 : dl 1.3 * @throws NullPointerException if the specified element is null and this
235 : jsr166 1.8 * 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 : dl 1.1 */
239 :     boolean offerLast(E e);
240 :    
241 :     /**
242 : jsr166 1.8 * Retrieves and removes the first element of this deque. This method
243 : jsr166 1.15 * differs from {@link #pollFirst pollFirst} only in that it throws an
244 :     * exception if this deque is empty.
245 : dl 1.1 *
246 : jsr166 1.8 * @return the head of this deque
247 :     * @throws NoSuchElementException if this deque is empty
248 : dl 1.1 */
249 : jsr166 1.8 E removeFirst();
250 : dl 1.1
251 :     /**
252 : jsr166 1.8 * Retrieves and removes the last element of this deque. This method
253 : jsr166 1.15 * differs from {@link #pollLast pollLast} only in that it throws an
254 :     * exception if this deque is empty.
255 : dl 1.1 *
256 : jsr166 1.8 * @return the tail of this deque
257 :     * @throws NoSuchElementException if this deque is empty
258 : dl 1.1 */
259 : jsr166 1.8 E removeLast();
260 : dl 1.1
261 :     /**
262 : jsr166 1.8 * Retrieves and removes the first element of this deque,
263 :     * or returns <tt>null</tt> if this deque is empty.
264 : dl 1.1 *
265 : jsr166 1.8 * @return the head of this deque, or <tt>null</tt> if this deque is empty
266 : dl 1.1 */
267 :     E pollFirst();
268 :    
269 :     /**
270 : jsr166 1.8 * Retrieves and removes the last element of this deque,
271 :     * or returns <tt>null</tt> if this deque is empty.
272 : dl 1.1 *
273 : jsr166 1.8 * @return the tail of this deque, or <tt>null</tt> if this deque is empty
274 : dl 1.1 */
275 :     E pollLast();
276 :    
277 :     /**
278 : jsr166 1.8 * Retrieves, but does not remove, the first element of this deque.
279 : jsr166 1.16 *
280 : jsr166 1.15 * This method differs from {@link #peekFirst peekFirst} only in that it
281 :     * throws an exception if this deque is empty.
282 : dl 1.1 *
283 : jsr166 1.8 * @return the head of this deque
284 : dl 1.1 * @throws NoSuchElementException if this deque is empty
285 :     */
286 : jsr166 1.8 E getFirst();
287 : dl 1.1
288 :     /**
289 : jsr166 1.8 * Retrieves, but does not remove, the last element of this deque.
290 : jsr166 1.15 * This method differs from {@link #peekLast peekLast} only in that it
291 :     * throws an exception if this deque is empty.
292 : dl 1.1 *
293 : jsr166 1.8 * @return the tail of this deque
294 : dl 1.1 * @throws NoSuchElementException if this deque is empty
295 :     */
296 : jsr166 1.8 E getLast();
297 : dl 1.1
298 :     /**
299 :     * Retrieves, but does not remove, the first element of this deque,
300 : jsr166 1.8 * or returns <tt>null</tt> if this deque is empty.
301 : dl 1.1 *
302 : jsr166 1.8 * @return the head of this deque, or <tt>null</tt> if this deque is empty
303 : dl 1.1 */
304 :     E peekFirst();
305 :    
306 :     /**
307 :     * Retrieves, but does not remove, the last element of this deque,
308 : jsr166 1.8 * or returns <tt>null</tt> if this deque is empty.
309 : dl 1.1 *
310 : jsr166 1.8 * @return the tail of this deque, or <tt>null</tt> if this deque is empty
311 : dl 1.1 */
312 :     E peekLast();
313 :    
314 :     /**
315 : jsr166 1.8 * 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 <tt>e</tt> such that
318 : jsr166 1.9 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>
319 :     * (if such an element exists).
320 : jsr166 1.12 * Returns <tt>true</tt> if this deque contained the specified element
321 :     * (or equivalently, if this deque changed as a result of the call).
322 : dl 1.1 *
323 : dl 1.3 * @param o element to be removed from this deque, if present
324 : jsr166 1.8 * @return <tt>true</tt> if an element was removed as a result of this call
325 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
326 :     * is incompatible with this deque (optional)
327 : dl 1.4 * @throws NullPointerException if the specified element is null and this
328 : jsr166 1.8 * deque does not permit null elements (optional)
329 : dl 1.1 */
330 : dl 1.3 boolean removeFirstOccurrence(Object o);
331 : dl 1.1
332 :     /**
333 : jsr166 1.8 * Removes the last occurrence of the specified element from this deque.
334 :     * If the deque does not contain the element, it is unchanged.
335 :     * More formally, removes the last element <tt>e</tt> such that
336 : jsr166 1.9 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>
337 :     * (if such an element exists).
338 : jsr166 1.12 * Returns <tt>true</tt> if this deque contained the specified element
339 :     * (or equivalently, if this deque changed as a result of the call).
340 : dl 1.1 *
341 : dl 1.3 * @param o element to be removed from this deque, if present
342 : jsr166 1.8 * @return <tt>true</tt> if an element was removed as a result of this call
343 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
344 :     * is incompatible with this deque (optional)
345 : dl 1.4 * @throws NullPointerException if the specified element is null and this
346 : jsr166 1.8 * deque does not permit null elements (optional)
347 : dl 1.1 */
348 : dl 1.3 boolean removeLastOccurrence(Object o);
349 : dl 1.1
350 : jsr166 1.8 // *** Queue methods ***
351 : dl 1.1
352 : jsr166 1.8 /**
353 :     * Inserts the specified element into the queue represented by this deque
354 :     * (in other words, at the tail of this deque) if it is possible to do so
355 :     * immediately without violating capacity restrictions, returning
356 :     * <tt>true</tt> upon success and throwing an
357 :     * <tt>IllegalStateException</tt> if no space is currently available.
358 :     * When using a capacity-restricted deque, it is generally preferable to
359 :     * use {@link #offer(Object) offer}.
360 :     *
361 : jsr166 1.14 * <p>This method is equivalent to {@link #addLast}.
362 : jsr166 1.8 *
363 :     * @param e the element to add
364 : jsr166 1.15 * @return <tt>true</tt> (as specified by {@link Collection#add})
365 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
366 :     * time due to capacity restrictions
367 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
368 :     * prevents it from being added to this deque
369 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
370 :     * deque does not permit null elements
371 :     * @throws IllegalArgumentException if some property of the specified
372 :     * element prevents it from being added to this deque
373 :     */
374 :     boolean add(E e);
375 : dl 1.1
376 :     /**
377 :     * Inserts the specified element into the queue represented by this deque
378 : jsr166 1.8 * (in other words, at the tail of this deque) if it is possible to do so
379 :     * immediately without violating capacity restrictions, returning
380 :     * <tt>true</tt> upon success and <tt>false</tt> if no space is currently
381 :     * available. When using a capacity-restricted deque, this method is
382 :     * generally preferable to the {@link #add} method, which can fail to
383 :     * insert an element only by throwing an exception.
384 : dl 1.1 *
385 :     * <p>This method is equivalent to {@link #offerLast}.
386 :     *
387 : jsr166 1.8 * @param e the element to add
388 :     * @return <tt>true</tt> if the element was added to this deque, else
389 :     * <tt>false</tt>
390 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
391 :     * prevents it from being added to this deque
392 : dl 1.3 * @throws NullPointerException if the specified element is null and this
393 : jsr166 1.8 * deque does not permit null elements
394 :     * @throws IllegalArgumentException if some property of the specified
395 :     * element prevents it from being added to this deque
396 : dl 1.1 */
397 :     boolean offer(E e);
398 :    
399 :     /**
400 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
401 :     * (in other words, the first element of this deque).
402 : jsr166 1.15 * This method differs from {@link #poll poll} only in that it throws an
403 : jsr166 1.8 * exception if this deque is empty.
404 : dl 1.1 *
405 : jsr166 1.8 * <p>This method is equivalent to {@link #removeFirst()}.
406 : dl 1.1 *
407 : jsr166 1.8 * @return the head of the queue represented by this deque
408 :     * @throws NoSuchElementException if this deque is empty
409 : dl 1.1 */
410 : jsr166 1.8 E remove();
411 : dl 1.1
412 :     /**
413 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
414 :     * (in other words, the first element of this deque), or returns
415 :     * <tt>null</tt> if this deque is empty.
416 : dl 1.1 *
417 :     * <p>This method is equivalent to {@link #pollFirst()}.
418 :     *
419 :     * @return the first element of this deque, or <tt>null</tt> if
420 : jsr166 1.8 * this deque is empty
421 : dl 1.1 */
422 :     E poll();
423 :    
424 :     /**
425 : jsr166 1.8 * Retrieves, but does not remove, the head of the queue represented by
426 :     * this deque (in other words, the first element of this deque).
427 : jsr166 1.15 * This method differs from {@link #peek peek} only in that it throws an
428 : jsr166 1.8 * exception if this deque is empty.
429 : dl 1.1 *
430 : jsr166 1.8 * <p>This method is equivalent to {@link #getFirst()}.
431 : dl 1.1 *
432 :     * @return the head of the queue represented by this deque
433 :     * @throws NoSuchElementException if this deque is empty
434 :     */
435 : jsr166 1.8 E element();
436 : dl 1.1
437 :     /**
438 :     * Retrieves, but does not remove, the head of the queue represented by
439 : jsr166 1.8 * this deque (in other words, the first element of this deque), or
440 :     * returns <tt>null</tt> if this deque is empty.
441 : dl 1.1 *
442 : dl 1.3 * <p>This method is equivalent to {@link #peekFirst()}.
443 : dl 1.1 *
444 :     * @return the head of the queue represented by this deque, or
445 : jsr166 1.8 * <tt>null</tt> if this deque is empty
446 : dl 1.1 */
447 :     E peek();
448 :    
449 :    
450 :     // *** Stack methods ***
451 :    
452 :     /**
453 : jsr166 1.8 * Pushes an element onto the stack represented by this deque (in other
454 :     * words, at the head of this deque) if it is possible to do so
455 :     * immediately without violating capacity restrictions, returning
456 :     * <tt>true</tt> upon success and throwing an
457 :     * <tt>IllegalStateException</tt> if no space is currently available.
458 : dl 1.1 *
459 :     * <p>This method is equivalent to {@link #addFirst}.
460 :     *
461 : dl 1.3 * @param e the element to push
462 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
463 :     * time due to capacity restrictions
464 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
465 :     * prevents it from being added to this deque
466 : dl 1.3 * @throws NullPointerException if the specified element is null and this
467 : jsr166 1.8 * deque does not permit null elements
468 :     * @throws IllegalArgumentException if some property of the specified
469 :     * element prevents it from being added to this deque
470 : dl 1.1 */
471 :     void push(E e);
472 :    
473 :     /**
474 :     * Pops an element from the stack represented by this deque. In other
475 : dl 1.2 * words, removes and returns the first element of this deque.
476 : dl 1.1 *
477 :     * <p>This method is equivalent to {@link #removeFirst()}.
478 :     *
479 :     * @return the element at the front of this deque (which is the top
480 : jsr166 1.8 * of the stack represented by this deque)
481 : dl 1.1 * @throws NoSuchElementException if this deque is empty
482 :     */
483 :     E pop();
484 :    
485 :    
486 : jsr166 1.8 // *** Collection methods ***
487 :    
488 :     /**
489 :     * Removes the first occurrence of the specified element from this deque.
490 :     * If the deque does not contain the element, it is unchanged.
491 :     * More formally, removes the first element <tt>e</tt> such that
492 : jsr166 1.9 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>
493 :     * (if such an element exists).
494 : jsr166 1.12 * Returns <tt>true</tt> if this deque contained the specified element
495 :     * (or equivalently, if this deque changed as a result of the call).
496 : jsr166 1.8 *
497 :     * <p>This method is equivalent to {@link #removeFirstOccurrence}.
498 :     *
499 :     * @param o element to be removed from this deque, if present
500 :     * @return <tt>true</tt> if an element was removed as a result of this call
501 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
502 :     * is incompatible with this deque (optional)
503 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
504 :     * deque does not permit null elements (optional)
505 :     */
506 :     boolean remove(Object o);
507 :    
508 :     /**
509 :     * Returns <tt>true</tt> if this deque contains the specified element.
510 : jsr166 1.9 * More formally, returns <tt>true</tt> if and only if this deque contains
511 :     * at least one element <tt>e</tt> such that
512 :     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
513 : jsr166 1.8 *
514 :     * @param o element whose presence in this deque is to be tested
515 :     * @return <tt>true</tt> if this deque contains the specified element
516 :     * @throws ClassCastException if the type of the specified element
517 :     * is incompatible with this deque (optional)
518 :     * @throws NullPointerException if the specified element is null and this
519 :     * deque does not permit null elements (optional)
520 :     */
521 :     boolean contains(Object o);
522 :    
523 :     /**
524 :     * Returns the number of elements in this deque.
525 :     *
526 :     * @return the number of elements in this deque
527 :     */
528 :     public int size();
529 : dl 1.1
530 :     /**
531 : jsr166 1.10 * Returns an iterator over the elements in this deque in proper sequence.
532 :     * The elements will be returned in order from first (head) to last (tail).
533 : dl 1.3 *
534 : jsr166 1.10 * @return an iterator over the elements in this deque in proper sequence
535 : dl 1.1 */
536 :     Iterator<E> iterator();
537 : dl 1.17
538 :     /**
539 :     * Returns an iterator over the elements in this deque in reverse
540 :     * sequential order. The elements will be returned in order from
541 :     * last (tail) to first (head).
542 :     *
543 :     * @return an iterator over the elements in this deque in reverse
544 :     * sequence
545 :     */
546 :     Iterator<E> descendingIterator();
547 :    
548 : dl 1.1 }

Doug Lea
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