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| 1 | /* | ||
| 2 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 3 | * | ||
| 4 | * This code is free software; you can redistribute it and/or modify it | ||
| 5 | * under the terms of the GNU General Public License version 2 only, as | ||
| 6 | * published by the Free Software Foundation. Oracle designates this | ||
| 7 | * particular file as subject to the "Classpath" exception as provided | ||
| 8 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 9 | * | ||
| 10 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 13 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 14 | * accompanied this code). | ||
| 15 | * | ||
| 16 | * You should have received a copy of the GNU General Public License version | ||
| 17 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 19 | * | ||
| 20 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 21 | * or visit www.oracle.com if you need additional information or have any | ||
| 22 | * questions. | ||
| 23 | */ | ||
| 24 | |||
| 25 | /* | ||
| 26 | * This file is available under and governed by the GNU General Public | ||
| 27 | * License version 2 only, as published by the Free Software Foundation. | ||
| 28 | * However, the following notice accompanied the original version of this | ||
| 29 | * file: | ||
| 30 | * | ||
| 31 | * Written by Doug Lea and Josh Bloch with assistance from members of | ||
| 32 | * JCP JSR-166 Expert Group and released to the public domain, as explained | ||
| 33 | * at http://creativecommons.org/publicdomain/zero/1.0/ | ||
| 34 | */ | ||
| 35 | |||
| 36 | package java.util; | ||
| 37 | |||
| 38 | /** | ||
| 39 | * A linear collection that supports element insertion and removal at | ||
| 40 | * both ends. The name <i>deque</i> is short for "double ended queue" | ||
| 41 | * and is usually pronounced "deck". Most <tt>Deque</tt> | ||
| 42 | * implementations place no fixed limits on the number of elements | ||
| 43 | * they may contain, but this interface supports capacity-restricted | ||
| 44 | * deques as well as those with no fixed size limit. | ||
| 45 | * | ||
| 46 | * <p>This interface defines methods to access the elements at both | ||
| 47 | * ends of the deque. Methods are provided to insert, remove, and | ||
| 48 | * examine the element. Each of these methods exists in two forms: | ||
| 49 | * one throws an exception if the operation fails, the other returns a | ||
| 50 | * special value (either <tt>null</tt> or <tt>false</tt>, depending on | ||
| 51 | * the operation). The latter form of the insert operation is | ||
| 52 | * designed specifically for use with capacity-restricted | ||
| 53 | * <tt>Deque</tt> implementations; in most implementations, insert | ||
| 54 | * operations cannot fail. | ||
| 55 | * | ||
| 56 | * <p>The twelve methods described above are summarized in the | ||
| 57 | * following table: | ||
| 58 | * | ||
| 59 | * <p> | ||
| 60 | * <table BORDER CELLPADDING=3 CELLSPACING=1> | ||
| 61 | * <tr> | ||
| 62 | * <td></td> | ||
| 63 | * <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td> | ||
| 64 | * <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td> | ||
| 65 | * </tr> | ||
| 66 | * <tr> | ||
| 67 | * <td></td> | ||
| 68 | * <td ALIGN=CENTER><em>Throws exception</em></td> | ||
| 69 | * <td ALIGN=CENTER><em>Special value</em></td> | ||
| 70 | * <td ALIGN=CENTER><em>Throws exception</em></td> | ||
| 71 | * <td ALIGN=CENTER><em>Special value</em></td> | ||
| 72 | * </tr> | ||
| 73 | * <tr> | ||
| 74 | * <td><b>Insert</b></td> | ||
| 75 | * <td>{@link #addFirst addFirst(e)}</td> | ||
| 76 | * <td>{@link #offerFirst offerFirst(e)}</td> | ||
| 77 | * <td>{@link #addLast addLast(e)}</td> | ||
| 78 | * <td>{@link #offerLast offerLast(e)}</td> | ||
| 79 | * </tr> | ||
| 80 | * <tr> | ||
| 81 | * <td><b>Remove</b></td> | ||
| 82 | * <td>{@link #removeFirst removeFirst()}</td> | ||
| 83 | * <td>{@link #pollFirst pollFirst()}</td> | ||
| 84 | * <td>{@link #removeLast removeLast()}</td> | ||
| 85 | * <td>{@link #pollLast pollLast()}</td> | ||
| 86 | * </tr> | ||
| 87 | * <tr> | ||
| 88 | * <td><b>Examine</b></td> | ||
| 89 | * <td>{@link #getFirst getFirst()}</td> | ||
| 90 | * <td>{@link #peekFirst peekFirst()}</td> | ||
| 91 | * <td>{@link #getLast getLast()}</td> | ||
| 92 | * <td>{@link #peekLast peekLast()}</td> | ||
| 93 | * </tr> | ||
| 94 | * </table> | ||
| 95 | * | ||
| 96 | * <p>This interface extends the {@link Queue} interface. When a deque is | ||
| 97 | * used as a queue, FIFO (First-In-First-Out) behavior results. Elements are | ||
| 98 | * added at the end of the deque and removed from the beginning. The methods | ||
| 99 | * inherited from the <tt>Queue</tt> interface are precisely equivalent to | ||
| 100 | * <tt>Deque</tt> methods as indicated in the following table: | ||
| 101 | * | ||
| 102 | * <p> | ||
| 103 | * <table BORDER CELLPADDING=3 CELLSPACING=1> | ||
| 104 | * <tr> | ||
| 105 | * <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td> | ||
| 106 | * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> | ||
| 107 | * </tr> | ||
| 108 | * <tr> | ||
| 109 | * <td>{@link java.util.Queue#add add(e)}</td> | ||
| 110 | * <td>{@link #addLast addLast(e)}</td> | ||
| 111 | * </tr> | ||
| 112 | * <tr> | ||
| 113 | * <td>{@link java.util.Queue#offer offer(e)}</td> | ||
| 114 | * <td>{@link #offerLast offerLast(e)}</td> | ||
| 115 | * </tr> | ||
| 116 | * <tr> | ||
| 117 | * <td>{@link java.util.Queue#remove remove()}</td> | ||
| 118 | * <td>{@link #removeFirst removeFirst()}</td> | ||
| 119 | * </tr> | ||
| 120 | * <tr> | ||
| 121 | * <td>{@link java.util.Queue#poll poll()}</td> | ||
| 122 | * <td>{@link #pollFirst pollFirst()}</td> | ||
| 123 | * </tr> | ||
| 124 | * <tr> | ||
| 125 | * <td>{@link java.util.Queue#element element()}</td> | ||
| 126 | * <td>{@link #getFirst getFirst()}</td> | ||
| 127 | * </tr> | ||
| 128 | * <tr> | ||
| 129 | * <td>{@link java.util.Queue#peek peek()}</td> | ||
| 130 | * <td>{@link #peek peekFirst()}</td> | ||
| 131 | * </tr> | ||
| 132 | * </table> | ||
| 133 | * | ||
| 134 | * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This | ||
| 135 | * interface should be used in preference to the legacy {@link Stack} class. | ||
| 136 | * When a deque is used as a stack, elements are pushed and popped from the | ||
| 137 | * beginning of the deque. Stack methods are precisely equivalent to | ||
| 138 | * <tt>Deque</tt> methods as indicated in the table below: | ||
| 139 | * | ||
| 140 | * <p> | ||
| 141 | * <table BORDER CELLPADDING=3 CELLSPACING=1> | ||
| 142 | * <tr> | ||
| 143 | * <td ALIGN=CENTER> <b>Stack Method</b></td> | ||
| 144 | * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> | ||
| 145 | * </tr> | ||
| 146 | * <tr> | ||
| 147 | * <td>{@link #push push(e)}</td> | ||
| 148 | * <td>{@link #addFirst addFirst(e)}</td> | ||
| 149 | * </tr> | ||
| 150 | * <tr> | ||
| 151 | * <td>{@link #pop pop()}</td> | ||
| 152 | * <td>{@link #removeFirst removeFirst()}</td> | ||
| 153 | * </tr> | ||
| 154 | * <tr> | ||
| 155 | * <td>{@link #peek peek()}</td> | ||
| 156 | * <td>{@link #peekFirst peekFirst()}</td> | ||
| 157 | * </tr> | ||
| 158 | * </table> | ||
| 159 | * | ||
| 160 | * <p>Note that the {@link #peek peek} method works equally well when | ||
| 161 | * a deque is used as a queue or a stack; in either case, elements are | ||
| 162 | * drawn from the beginning of the deque. | ||
| 163 | * | ||
| 164 | * <p>This interface provides two methods to remove interior | ||
| 165 | * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and | ||
| 166 | * {@link #removeLastOccurrence removeLastOccurrence}. | ||
| 167 | * | ||
| 168 | * <p>Unlike the {@link List} interface, this interface does not | ||
| 169 | * provide support for indexed access to elements. | ||
| 170 | * | ||
| 171 | * <p>While <tt>Deque</tt> implementations are not strictly required | ||
| 172 | * to prohibit the insertion of null elements, they are strongly | ||
| 173 | * encouraged to do so. Users of any <tt>Deque</tt> implementations | ||
| 174 | * that do allow null elements are strongly encouraged <i>not</i> to | ||
| 175 | * take advantage of the ability to insert nulls. This is so because | ||
| 176 | * <tt>null</tt> is used as a special return value by various methods | ||
| 177 | * to indicated that the deque is empty. | ||
| 178 | * | ||
| 179 | * <p><tt>Deque</tt> implementations generally do not define | ||
| 180 | * element-based versions of the <tt>equals</tt> and <tt>hashCode</tt> | ||
| 181 | * methods, but instead inherit the identity-based versions from class | ||
| 182 | * <tt>Object</tt>. | ||
| 183 | * | ||
| 184 | * <p>This interface is a member of the <a | ||
| 185 | * href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections | ||
| 186 | * Framework</a>. | ||
| 187 | * | ||
| 188 | * @author Doug Lea | ||
| 189 | * @author Josh Bloch | ||
| 190 | * @since 1.6 | ||
| 191 | * @param <E> the type of elements held in this collection | ||
| 192 | */ | ||
| 193 | |||
| 194 | public interface Deque<E> extends Queue<E> { | ||
| 195 | /** | ||
| 196 | * Inserts the specified element at the front of this deque if it is | ||
| 197 | * possible to do so immediately without violating capacity restrictions. | ||
| 198 | * When using a capacity-restricted deque, it is generally preferable to | ||
| 199 | * use method {@link #offerFirst}. | ||
| 200 | * | ||
| 201 | * @param e the element to add | ||
| 202 | * @throws IllegalStateException if the element cannot be added at this | ||
| 203 | * time due to capacity restrictions | ||
| 204 | * @throws ClassCastException if the class of the specified element | ||
| 205 | * prevents it from being added to this deque | ||
| 206 | * @throws NullPointerException if the specified element is null and this | ||
| 207 | * deque does not permit null elements | ||
| 208 | * @throws IllegalArgumentException if some property of the specified | ||
| 209 | * element prevents it from being added to this deque | ||
| 210 | */ | ||
| 211 | void addFirst(E e); | ||
| 212 | |||
| 213 | /** | ||
| 214 | * Inserts the specified element at the end of this deque if it is | ||
| 215 | * possible to do so immediately without violating capacity restrictions. | ||
| 216 | * When using a capacity-restricted deque, it is generally preferable to | ||
| 217 | * use method {@link #offerLast}. | ||
| 218 | * | ||
| 219 | * <p>This method is equivalent to {@link #add}. | ||
| 220 | * | ||
| 221 | * @param e the element to add | ||
| 222 | * @throws IllegalStateException if the element cannot be added at this | ||
| 223 | * time due to capacity restrictions | ||
| 224 | * @throws ClassCastException if the class of the specified element | ||
| 225 | * prevents it from being added to this deque | ||
| 226 | * @throws NullPointerException if the specified element is null and this | ||
| 227 | * deque does not permit null elements | ||
| 228 | * @throws IllegalArgumentException if some property of the specified | ||
| 229 | * element prevents it from being added to this deque | ||
| 230 | */ | ||
| 231 | void addLast(E e); | ||
| 232 | |||
| 233 | /** | ||
| 234 | * Inserts the specified element at the front of this deque unless it would | ||
| 235 | * violate capacity restrictions. When using a capacity-restricted deque, | ||
| 236 | * this method is generally preferable to the {@link #addFirst} method, | ||
| 237 | * which can fail to insert an element only by throwing an exception. | ||
| 238 | * | ||
| 239 | * @param e the element to add | ||
| 240 | * @return <tt>true</tt> if the element was added to this deque, else | ||
| 241 | * <tt>false</tt> | ||
| 242 | * @throws ClassCastException if the class of the specified element | ||
| 243 | * prevents it from being added to this deque | ||
| 244 | * @throws NullPointerException if the specified element is null and this | ||
| 245 | * deque does not permit null elements | ||
| 246 | * @throws IllegalArgumentException if some property of the specified | ||
| 247 | * element prevents it from being added to this deque | ||
| 248 | */ | ||
| 249 | boolean offerFirst(E e); | ||
| 250 | |||
| 251 | /** | ||
| 252 | * Inserts the specified element at the end of this deque unless it would | ||
| 253 | * violate capacity restrictions. When using a capacity-restricted deque, | ||
| 254 | * this method is generally preferable to the {@link #addLast} method, | ||
| 255 | * which can fail to insert an element only by throwing an exception. | ||
| 256 | * | ||
| 257 | * @param e the element to add | ||
| 258 | * @return <tt>true</tt> if the element was added to this deque, else | ||
| 259 | * <tt>false</tt> | ||
| 260 | * @throws ClassCastException if the class of the specified element | ||
| 261 | * prevents it from being added to this deque | ||
| 262 | * @throws NullPointerException if the specified element is null and this | ||
| 263 | * deque does not permit null elements | ||
| 264 | * @throws IllegalArgumentException if some property of the specified | ||
| 265 | * element prevents it from being added to this deque | ||
| 266 | */ | ||
| 267 | boolean offerLast(E e); | ||
| 268 | |||
| 269 | /** | ||
| 270 | * Retrieves and removes the first element of this deque. This method | ||
| 271 | * differs from {@link #pollFirst pollFirst} only in that it throws an | ||
| 272 | * exception if this deque is empty. | ||
| 273 | * | ||
| 274 | * @return the head of this deque | ||
| 275 | * @throws NoSuchElementException if this deque is empty | ||
| 276 | */ | ||
| 277 | E removeFirst(); | ||
| 278 | |||
| 279 | /** | ||
| 280 | * Retrieves and removes the last element of this deque. This method | ||
| 281 | * differs from {@link #pollLast pollLast} only in that it throws an | ||
| 282 | * exception if this deque is empty. | ||
| 283 | * | ||
| 284 | * @return the tail of this deque | ||
| 285 | * @throws NoSuchElementException if this deque is empty | ||
| 286 | */ | ||
| 287 | E removeLast(); | ||
| 288 | |||
| 289 | /** | ||
| 290 | * Retrieves and removes the first element of this deque, | ||
| 291 | * or returns <tt>null</tt> if this deque is empty. | ||
| 292 | * | ||
| 293 | * @return the head of this deque, or <tt>null</tt> if this deque is empty | ||
| 294 | */ | ||
| 295 | E pollFirst(); | ||
| 296 | |||
| 297 | /** | ||
| 298 | * Retrieves and removes the last element of this deque, | ||
| 299 | * or returns <tt>null</tt> if this deque is empty. | ||
| 300 | * | ||
| 301 | * @return the tail of this deque, or <tt>null</tt> if this deque is empty | ||
| 302 | */ | ||
| 303 | E pollLast(); | ||
| 304 | |||
| 305 | /** | ||
| 306 | * Retrieves, but does not remove, the first element of this deque. | ||
| 307 | * | ||
| 308 | * This method differs from {@link #peekFirst peekFirst} only in that it | ||
| 309 | * throws an exception if this deque is empty. | ||
| 310 | * | ||
| 311 | * @return the head of this deque | ||
| 312 | * @throws NoSuchElementException if this deque is empty | ||
| 313 | */ | ||
| 314 | E getFirst(); | ||
| 315 | |||
| 316 | /** | ||
| 317 | * Retrieves, but does not remove, the last element of this deque. | ||
| 318 | * This method differs from {@link #peekLast peekLast} only in that it | ||
| 319 | * throws an exception if this deque is empty. | ||
| 320 | * | ||
| 321 | * @return the tail of this deque | ||
| 322 | * @throws NoSuchElementException if this deque is empty | ||
| 323 | */ | ||
| 324 | E getLast(); | ||
| 325 | |||
| 326 | /** | ||
| 327 | * Retrieves, but does not remove, the first element of this deque, | ||
| 328 | * or returns <tt>null</tt> if this deque is empty. | ||
| 329 | * | ||
| 330 | * @return the head of this deque, or <tt>null</tt> if this deque is empty | ||
| 331 | */ | ||
| 332 | E peekFirst(); | ||
| 333 | |||
| 334 | /** | ||
| 335 | * Retrieves, but does not remove, the last element of this deque, | ||
| 336 | * or returns <tt>null</tt> if this deque is empty. | ||
| 337 | * | ||
| 338 | * @return the tail of this deque, or <tt>null</tt> if this deque is empty | ||
| 339 | */ | ||
| 340 | E peekLast(); | ||
| 341 | |||
| 342 | /** | ||
| 343 | * Removes the first occurrence of the specified element from this deque. | ||
| 344 | * If the deque does not contain the element, it is unchanged. | ||
| 345 | * More formally, removes the first element <tt>e</tt> such that | ||
| 346 | * <tt>(o==null ? e==null : o.equals(e))</tt> | ||
| 347 | * (if such an element exists). | ||
| 348 | * Returns <tt>true</tt> if this deque contained the specified element | ||
| 349 | * (or equivalently, if this deque changed as a result of the call). | ||
| 350 | * | ||
| 351 | * @param o element to be removed from this deque, if present | ||
| 352 | * @return <tt>true</tt> if an element was removed as a result of this call | ||
| 353 | * @throws ClassCastException if the class of the specified element | ||
| 354 | * is incompatible with this deque | ||
| 355 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 356 | * @throws NullPointerException if the specified element is null and this | ||
| 357 | * deque does not permit null elements | ||
| 358 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 359 | */ | ||
| 360 | boolean removeFirstOccurrence(Object o); | ||
| 361 | |||
| 362 | /** | ||
| 363 | * Removes the last occurrence of the specified element from this deque. | ||
| 364 | * If the deque does not contain the element, it is unchanged. | ||
| 365 | * More formally, removes the last element <tt>e</tt> such that | ||
| 366 | * <tt>(o==null ? e==null : o.equals(e))</tt> | ||
| 367 | * (if such an element exists). | ||
| 368 | * Returns <tt>true</tt> if this deque contained the specified element | ||
| 369 | * (or equivalently, if this deque changed as a result of the call). | ||
| 370 | * | ||
| 371 | * @param o element to be removed from this deque, if present | ||
| 372 | * @return <tt>true</tt> if an element was removed as a result of this call | ||
| 373 | * @throws ClassCastException if the class of the specified element | ||
| 374 | * is incompatible with this deque | ||
| 375 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 376 | * @throws NullPointerException if the specified element is null and this | ||
| 377 | * deque does not permit null elements | ||
| 378 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 379 | */ | ||
| 380 | boolean removeLastOccurrence(Object o); | ||
| 381 | |||
| 382 | // *** Queue methods *** | ||
| 383 | |||
| 384 | /** | ||
| 385 | * Inserts the specified element into the queue represented by this deque | ||
| 386 | * (in other words, at the tail of this deque) if it is possible to do so | ||
| 387 | * immediately without violating capacity restrictions, returning | ||
| 388 | * <tt>true</tt> upon success and throwing an | ||
| 389 | * <tt>IllegalStateException</tt> if no space is currently available. | ||
| 390 | * When using a capacity-restricted deque, it is generally preferable to | ||
| 391 | * use {@link #offer(Object) offer}. | ||
| 392 | * | ||
| 393 | * <p>This method is equivalent to {@link #addLast}. | ||
| 394 | * | ||
| 395 | * @param e the element to add | ||
| 396 | * @return <tt>true</tt> (as specified by {@link Collection#add}) | ||
| 397 | * @throws IllegalStateException if the element cannot be added at this | ||
| 398 | * time due to capacity restrictions | ||
| 399 | * @throws ClassCastException if the class of the specified element | ||
| 400 | * prevents it from being added to this deque | ||
| 401 | * @throws NullPointerException if the specified element is null and this | ||
| 402 | * deque does not permit null elements | ||
| 403 | * @throws IllegalArgumentException if some property of the specified | ||
| 404 | * element prevents it from being added to this deque | ||
| 405 | */ | ||
| 406 | boolean add(E e); | ||
| 407 | |||
| 408 | /** | ||
| 409 | * Inserts the specified element into the queue represented by this deque | ||
| 410 | * (in other words, at the tail of this deque) if it is possible to do so | ||
| 411 | * immediately without violating capacity restrictions, returning | ||
| 412 | * <tt>true</tt> upon success and <tt>false</tt> if no space is currently | ||
| 413 | * available. When using a capacity-restricted deque, this method is | ||
| 414 | * generally preferable to the {@link #add} method, which can fail to | ||
| 415 | * insert an element only by throwing an exception. | ||
| 416 | * | ||
| 417 | * <p>This method is equivalent to {@link #offerLast}. | ||
| 418 | * | ||
| 419 | * @param e the element to add | ||
| 420 | * @return <tt>true</tt> if the element was added to this deque, else | ||
| 421 | * <tt>false</tt> | ||
| 422 | * @throws ClassCastException if the class of the specified element | ||
| 423 | * prevents it from being added to this deque | ||
| 424 | * @throws NullPointerException if the specified element is null and this | ||
| 425 | * deque does not permit null elements | ||
| 426 | * @throws IllegalArgumentException if some property of the specified | ||
| 427 | * element prevents it from being added to this deque | ||
| 428 | */ | ||
| 429 | boolean offer(E e); | ||
| 430 | |||
| 431 | /** | ||
| 432 | * Retrieves and removes the head of the queue represented by this deque | ||
| 433 | * (in other words, the first element of this deque). | ||
| 434 | * This method differs from {@link #poll poll} only in that it throws an | ||
| 435 | * exception if this deque is empty. | ||
| 436 | * | ||
| 437 | * <p>This method is equivalent to {@link #removeFirst()}. | ||
| 438 | * | ||
| 439 | * @return the head of the queue represented by this deque | ||
| 440 | * @throws NoSuchElementException if this deque is empty | ||
| 441 | */ | ||
| 442 | E remove(); | ||
| 443 | |||
| 444 | /** | ||
| 445 | * Retrieves and removes the head of the queue represented by this deque | ||
| 446 | * (in other words, the first element of this deque), or returns | ||
| 447 | * <tt>null</tt> if this deque is empty. | ||
| 448 | * | ||
| 449 | * <p>This method is equivalent to {@link #pollFirst()}. | ||
| 450 | * | ||
| 451 | * @return the first element of this deque, or <tt>null</tt> if | ||
| 452 | * this deque is empty | ||
| 453 | */ | ||
| 454 | E poll(); | ||
| 455 | |||
| 456 | /** | ||
| 457 | * Retrieves, but does not remove, the head of the queue represented by | ||
| 458 | * this deque (in other words, the first element of this deque). | ||
| 459 | * This method differs from {@link #peek peek} only in that it throws an | ||
| 460 | * exception if this deque is empty. | ||
| 461 | * | ||
| 462 | * <p>This method is equivalent to {@link #getFirst()}. | ||
| 463 | * | ||
| 464 | * @return the head of the queue represented by this deque | ||
| 465 | * @throws NoSuchElementException if this deque is empty | ||
| 466 | */ | ||
| 467 | E element(); | ||
| 468 | |||
| 469 | /** | ||
| 470 | * Retrieves, but does not remove, the head of the queue represented by | ||
| 471 | * this deque (in other words, the first element of this deque), or | ||
| 472 | * returns <tt>null</tt> if this deque is empty. | ||
| 473 | * | ||
| 474 | * <p>This method is equivalent to {@link #peekFirst()}. | ||
| 475 | * | ||
| 476 | * @return the head of the queue represented by this deque, or | ||
| 477 | * <tt>null</tt> if this deque is empty | ||
| 478 | */ | ||
| 479 | E peek(); | ||
| 480 | |||
| 481 | |||
| 482 | // *** Stack methods *** | ||
| 483 | |||
| 484 | /** | ||
| 485 | * Pushes an element onto the stack represented by this deque (in other | ||
| 486 | * words, at the head of this deque) if it is possible to do so | ||
| 487 | * immediately without violating capacity restrictions, returning | ||
| 488 | * <tt>true</tt> upon success and throwing an | ||
| 489 | * <tt>IllegalStateException</tt> if no space is currently available. | ||
| 490 | * | ||
| 491 | * <p>This method is equivalent to {@link #addFirst}. | ||
| 492 | * | ||
| 493 | * @param e the element to push | ||
| 494 | * @throws IllegalStateException if the element cannot be added at this | ||
| 495 | * time due to capacity restrictions | ||
| 496 | * @throws ClassCastException if the class of the specified element | ||
| 497 | * prevents it from being added to this deque | ||
| 498 | * @throws NullPointerException if the specified element is null and this | ||
| 499 | * deque does not permit null elements | ||
| 500 | * @throws IllegalArgumentException if some property of the specified | ||
| 501 | * element prevents it from being added to this deque | ||
| 502 | */ | ||
| 503 | void push(E e); | ||
| 504 | |||
| 505 | /** | ||
| 506 | * Pops an element from the stack represented by this deque. In other | ||
| 507 | * words, removes and returns the first element of this deque. | ||
| 508 | * | ||
| 509 | * <p>This method is equivalent to {@link #removeFirst()}. | ||
| 510 | * | ||
| 511 | * @return the element at the front of this deque (which is the top | ||
| 512 | * of the stack represented by this deque) | ||
| 513 | * @throws NoSuchElementException if this deque is empty | ||
| 514 | */ | ||
| 515 | E pop(); | ||
| 516 | |||
| 517 | |||
| 518 | // *** Collection methods *** | ||
| 519 | |||
| 520 | /** | ||
| 521 | * Removes the first occurrence of the specified element from this deque. | ||
| 522 | * If the deque does not contain the element, it is unchanged. | ||
| 523 | * More formally, removes the first element <tt>e</tt> such that | ||
| 524 | * <tt>(o==null ? e==null : o.equals(e))</tt> | ||
| 525 | * (if such an element exists). | ||
| 526 | * Returns <tt>true</tt> if this deque contained the specified element | ||
| 527 | * (or equivalently, if this deque changed as a result of the call). | ||
| 528 | * | ||
| 529 | * <p>This method is equivalent to {@link #removeFirstOccurrence}. | ||
| 530 | * | ||
| 531 | * @param o element to be removed from this deque, if present | ||
| 532 | * @return <tt>true</tt> if an element was removed as a result of this call | ||
| 533 | * @throws ClassCastException if the class of the specified element | ||
| 534 | * is incompatible with this deque | ||
| 535 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 536 | * @throws NullPointerException if the specified element is null and this | ||
| 537 | * deque does not permit null elements | ||
| 538 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 539 | */ | ||
| 540 | boolean remove(Object o); | ||
| 541 | |||
| 542 | /** | ||
| 543 | * Returns <tt>true</tt> if this deque contains the specified element. | ||
| 544 | * More formally, returns <tt>true</tt> if and only if this deque contains | ||
| 545 | * at least one element <tt>e</tt> such that | ||
| 546 | * <tt>(o==null ? e==null : o.equals(e))</tt>. | ||
| 547 | * | ||
| 548 | * @param o element whose presence in this deque is to be tested | ||
| 549 | * @return <tt>true</tt> if this deque contains the specified element | ||
| 550 | * @throws ClassCastException if the type of the specified element | ||
| 551 | * is incompatible with this deque | ||
| 552 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 553 | * @throws NullPointerException if the specified element is null and this | ||
| 554 | * deque does not permit null elements | ||
| 555 | * (<a href="Collection.html#optional-restrictions">optional</a>) | ||
| 556 | */ | ||
| 557 | boolean contains(Object o); | ||
| 558 | |||
| 559 | /** | ||
| 560 | * Returns the number of elements in this deque. | ||
| 561 | * | ||
| 562 | * @return the number of elements in this deque | ||
| 563 | */ | ||
| 564 | public int size(); | ||
| 565 | |||
| 566 | /** | ||
| 567 | * Returns an iterator over the elements in this deque in proper sequence. | ||
| 568 | * The elements will be returned in order from first (head) to last (tail). | ||
| 569 | * | ||
| 570 | * @return an iterator over the elements in this deque in proper sequence | ||
| 571 | */ | ||
| 572 | Iterator<E> iterator(); | ||
| 573 | |||
| 574 | /** | ||
| 575 | * Returns an iterator over the elements in this deque in reverse | ||
| 576 | * sequential order. The elements will be returned in order from | ||
| 577 | * last (tail) to first (head). | ||
| 578 | * | ||
| 579 | * @return an iterator over the elements in this deque in reverse | ||
| 580 | * sequence | ||
| 581 | */ | ||
| 582 | Iterator<E> descendingIterator(); | ||
| 583 | |||
| 584 | } | ||