List.java revision 51b1b6997fd3f980076b8081f7f1165ccc2a4008
1/* 2 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26package java.util; 27 28/** 29 * An ordered collection (also known as a <i>sequence</i>). The user of this 30 * interface has precise control over where in the list each element is 31 * inserted. The user can access elements by their integer index (position in 32 * the list), and search for elements in the list.<p> 33 * 34 * Unlike sets, lists typically allow duplicate elements. More formally, 35 * lists typically allow pairs of elements <tt>e1</tt> and <tt>e2</tt> 36 * such that <tt>e1.equals(e2)</tt>, and they typically allow multiple 37 * null elements if they allow null elements at all. It is not inconceivable 38 * that someone might wish to implement a list that prohibits duplicates, by 39 * throwing runtime exceptions when the user attempts to insert them, but we 40 * expect this usage to be rare.<p> 41 * 42 * The <tt>List</tt> interface places additional stipulations, beyond those 43 * specified in the <tt>Collection</tt> interface, on the contracts of the 44 * <tt>iterator</tt>, <tt>add</tt>, <tt>remove</tt>, <tt>equals</tt>, and 45 * <tt>hashCode</tt> methods. Declarations for other inherited methods are 46 * also included here for convenience.<p> 47 * 48 * The <tt>List</tt> interface provides four methods for positional (indexed) 49 * access to list elements. Lists (like Java arrays) are zero based. Note 50 * that these operations may execute in time proportional to the index value 51 * for some implementations (the <tt>LinkedList</tt> class, for 52 * example). Thus, iterating over the elements in a list is typically 53 * preferable to indexing through it if the caller does not know the 54 * implementation.<p> 55 * 56 * The <tt>List</tt> interface provides a special iterator, called a 57 * <tt>ListIterator</tt>, that allows element insertion and replacement, and 58 * bidirectional access in addition to the normal operations that the 59 * <tt>Iterator</tt> interface provides. A method is provided to obtain a 60 * list iterator that starts at a specified position in the list.<p> 61 * 62 * The <tt>List</tt> interface provides two methods to search for a specified 63 * object. From a performance standpoint, these methods should be used with 64 * caution. In many implementations they will perform costly linear 65 * searches.<p> 66 * 67 * The <tt>List</tt> interface provides two methods to efficiently insert and 68 * remove multiple elements at an arbitrary point in the list.<p> 69 * 70 * Note: While it is permissible for lists to contain themselves as elements, 71 * extreme caution is advised: the <tt>equals</tt> and <tt>hashCode</tt> 72 * methods are no longer well defined on such a list. 73 * 74 * <p>Some list implementations have restrictions on the elements that 75 * they may contain. For example, some implementations prohibit null elements, 76 * and some have restrictions on the types of their elements. Attempting to 77 * add an ineligible element throws an unchecked exception, typically 78 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting 79 * to query the presence of an ineligible element may throw an exception, 80 * or it may simply return false; some implementations will exhibit the former 81 * behavior and some will exhibit the latter. More generally, attempting an 82 * operation on an ineligible element whose completion would not result in 83 * the insertion of an ineligible element into the list may throw an 84 * exception or it may succeed, at the option of the implementation. 85 * Such exceptions are marked as "optional" in the specification for this 86 * interface. 87 * 88 * <p>This interface is a member of the 89 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 90 * Java Collections Framework</a>. 91 * 92 * @param <E> the type of elements in this list 93 * 94 * @author Josh Bloch 95 * @author Neal Gafter 96 * @see Collection 97 * @see Set 98 * @see ArrayList 99 * @see LinkedList 100 * @see Vector 101 * @see Arrays#asList(Object[]) 102 * @see Collections#nCopies(int, Object) 103 * @see Collections#EMPTY_LIST 104 * @see AbstractList 105 * @see AbstractSequentialList 106 * @since 1.2 107 */ 108 109public interface List<E> extends Collection<E> { 110 // Query Operations 111 112 /** 113 * Returns the number of elements in this list. If this list contains 114 * more than <tt>Integer.MAX_VALUE</tt> elements, returns 115 * <tt>Integer.MAX_VALUE</tt>. 116 * 117 * @return the number of elements in this list 118 */ 119 int size(); 120 121 /** 122 * Returns <tt>true</tt> if this list contains no elements. 123 * 124 * @return <tt>true</tt> if this list contains no elements 125 */ 126 boolean isEmpty(); 127 128 /** 129 * Returns <tt>true</tt> if this list contains the specified element. 130 * More formally, returns <tt>true</tt> if and only if this list contains 131 * at least one element <tt>e</tt> such that 132 * <tt>(o==null ? e==null : o.equals(e))</tt>. 133 * 134 * @param o element whose presence in this list is to be tested 135 * @return <tt>true</tt> if this list contains the specified element 136 * @throws ClassCastException if the type of the specified element 137 * is incompatible with this list 138 * (<a href="Collection.html#optional-restrictions">optional</a>) 139 * @throws NullPointerException if the specified element is null and this 140 * list does not permit null elements 141 * (<a href="Collection.html#optional-restrictions">optional</a>) 142 */ 143 boolean contains(Object o); 144 145 /** 146 * Returns an iterator over the elements in this list in proper sequence. 147 * 148 * @return an iterator over the elements in this list in proper sequence 149 */ 150 Iterator<E> iterator(); 151 152 /** 153 * Returns an array containing all of the elements in this list in proper 154 * sequence (from first to last element). 155 * 156 * <p>The returned array will be "safe" in that no references to it are 157 * maintained by this list. (In other words, this method must 158 * allocate a new array even if this list is backed by an array). 159 * The caller is thus free to modify the returned array. 160 * 161 * <p>This method acts as bridge between array-based and collection-based 162 * APIs. 163 * 164 * @return an array containing all of the elements in this list in proper 165 * sequence 166 * @see Arrays#asList(Object[]) 167 */ 168 Object[] toArray(); 169 170 /** 171 * Returns an array containing all of the elements in this list in 172 * proper sequence (from first to last element); the runtime type of 173 * the returned array is that of the specified array. If the list fits 174 * in the specified array, it is returned therein. Otherwise, a new 175 * array is allocated with the runtime type of the specified array and 176 * the size of this list. 177 * 178 * <p>If the list fits in the specified array with room to spare (i.e., 179 * the array has more elements than the list), the element in the array 180 * immediately following the end of the list is set to <tt>null</tt>. 181 * (This is useful in determining the length of the list <i>only</i> if 182 * the caller knows that the list does not contain any null elements.) 183 * 184 * <p>Like the {@link #toArray()} method, this method acts as bridge between 185 * array-based and collection-based APIs. Further, this method allows 186 * precise control over the runtime type of the output array, and may, 187 * under certain circumstances, be used to save allocation costs. 188 * 189 * <p>Suppose <tt>x</tt> is a list known to contain only strings. 190 * The following code can be used to dump the list into a newly 191 * allocated array of <tt>String</tt>: 192 * 193 * <pre> 194 * String[] y = x.toArray(new String[0]);</pre> 195 * 196 * Note that <tt>toArray(new Object[0])</tt> is identical in function to 197 * <tt>toArray()</tt>. 198 * 199 * @param a the array into which the elements of this list are to 200 * be stored, if it is big enough; otherwise, a new array of the 201 * same runtime type is allocated for this purpose. 202 * @return an array containing the elements of this list 203 * @throws ArrayStoreException if the runtime type of the specified array 204 * is not a supertype of the runtime type of every element in 205 * this list 206 * @throws NullPointerException if the specified array is null 207 */ 208 <T> T[] toArray(T[] a); 209 210 211 // Modification Operations 212 213 /** 214 * Appends the specified element to the end of this list (optional 215 * operation). 216 * 217 * <p>Lists that support this operation may place limitations on what 218 * elements may be added to this list. In particular, some 219 * lists will refuse to add null elements, and others will impose 220 * restrictions on the type of elements that may be added. List 221 * classes should clearly specify in their documentation any restrictions 222 * on what elements may be added. 223 * 224 * @param e element to be appended to this list 225 * @return <tt>true</tt> (as specified by {@link Collection#add}) 226 * @throws UnsupportedOperationException if the <tt>add</tt> operation 227 * is not supported by this list 228 * @throws ClassCastException if the class of the specified element 229 * prevents it from being added to this list 230 * @throws NullPointerException if the specified element is null and this 231 * list does not permit null elements 232 * @throws IllegalArgumentException if some property of this element 233 * prevents it from being added to this list 234 */ 235 boolean add(E e); 236 237 /** 238 * Removes the first occurrence of the specified element from this list, 239 * if it is present (optional operation). If this list does not contain 240 * the element, it is unchanged. More formally, removes the element with 241 * the lowest index <tt>i</tt> such that 242 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> 243 * (if such an element exists). Returns <tt>true</tt> if this list 244 * contained the specified element (or equivalently, if this list changed 245 * as a result of the call). 246 * 247 * @param o element to be removed from this list, if present 248 * @return <tt>true</tt> if this list contained the specified element 249 * @throws ClassCastException if the type of the specified element 250 * is incompatible with this list 251 * (<a href="Collection.html#optional-restrictions">optional</a>) 252 * @throws NullPointerException if the specified element is null and this 253 * list does not permit null elements 254 * (<a href="Collection.html#optional-restrictions">optional</a>) 255 * @throws UnsupportedOperationException if the <tt>remove</tt> operation 256 * is not supported by this list 257 */ 258 boolean remove(Object o); 259 260 261 // Bulk Modification Operations 262 263 /** 264 * Returns <tt>true</tt> if this list contains all of the elements of the 265 * specified collection. 266 * 267 * @param c collection to be checked for containment in this list 268 * @return <tt>true</tt> if this list contains all of the elements of the 269 * specified collection 270 * @throws ClassCastException if the types of one or more elements 271 * in the specified collection are incompatible with this 272 * list 273 * (<a href="Collection.html#optional-restrictions">optional</a>) 274 * @throws NullPointerException if the specified collection contains one 275 * or more null elements and this list does not permit null 276 * elements 277 * (<a href="Collection.html#optional-restrictions">optional</a>), 278 * or if the specified collection is null 279 * @see #contains(Object) 280 */ 281 boolean containsAll(Collection<?> c); 282 283 /** 284 * Appends all of the elements in the specified collection to the end of 285 * this list, in the order that they are returned by the specified 286 * collection's iterator (optional operation). The behavior of this 287 * operation is undefined if the specified collection is modified while 288 * the operation is in progress. (Note that this will occur if the 289 * specified collection is this list, and it's nonempty.) 290 * 291 * @param c collection containing elements to be added to this list 292 * @return <tt>true</tt> if this list changed as a result of the call 293 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation 294 * is not supported by this list 295 * @throws ClassCastException if the class of an element of the specified 296 * collection prevents it from being added to this list 297 * @throws NullPointerException if the specified collection contains one 298 * or more null elements and this list does not permit null 299 * elements, or if the specified collection is null 300 * @throws IllegalArgumentException if some property of an element of the 301 * specified collection prevents it from being added to this list 302 * @see #add(Object) 303 */ 304 boolean addAll(Collection<? extends E> c); 305 306 /** 307 * Inserts all of the elements in the specified collection into this 308 * list at the specified position (optional operation). Shifts the 309 * element currently at that position (if any) and any subsequent 310 * elements to the right (increases their indices). The new elements 311 * will appear in this list in the order that they are returned by the 312 * specified collection's iterator. The behavior of this operation is 313 * undefined if the specified collection is modified while the 314 * operation is in progress. (Note that this will occur if the specified 315 * collection is this list, and it's nonempty.) 316 * 317 * @param index index at which to insert the first element from the 318 * specified collection 319 * @param c collection containing elements to be added to this list 320 * @return <tt>true</tt> if this list changed as a result of the call 321 * @throws UnsupportedOperationException if the <tt>addAll</tt> operation 322 * is not supported by this list 323 * @throws ClassCastException if the class of an element of the specified 324 * collection prevents it from being added to this list 325 * @throws NullPointerException if the specified collection contains one 326 * or more null elements and this list does not permit null 327 * elements, or if the specified collection is null 328 * @throws IllegalArgumentException if some property of an element of the 329 * specified collection prevents it from being added to this list 330 * @throws IndexOutOfBoundsException if the index is out of range 331 * (<tt>index < 0 || index > size()</tt>) 332 */ 333 boolean addAll(int index, Collection<? extends E> c); 334 335 /** 336 * Removes from this list all of its elements that are contained in the 337 * specified collection (optional operation). 338 * 339 * @param c collection containing elements to be removed from this list 340 * @return <tt>true</tt> if this list changed as a result of the call 341 * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation 342 * is not supported by this list 343 * @throws ClassCastException if the class of an element of this list 344 * is incompatible with the specified collection 345 * (<a href="Collection.html#optional-restrictions">optional</a>) 346 * @throws NullPointerException if this list contains a null element and the 347 * specified collection does not permit null elements 348 * (<a href="Collection.html#optional-restrictions">optional</a>), 349 * or if the specified collection is null 350 * @see #remove(Object) 351 * @see #contains(Object) 352 */ 353 boolean removeAll(Collection<?> c); 354 355 /** 356 * Retains only the elements in this list that are contained in the 357 * specified collection (optional operation). In other words, removes 358 * from this list all of its elements that are not contained in the 359 * specified collection. 360 * 361 * @param c collection containing elements to be retained in this list 362 * @return <tt>true</tt> if this list changed as a result of the call 363 * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation 364 * is not supported by this list 365 * @throws ClassCastException if the class of an element of this list 366 * is incompatible with the specified collection 367 * (<a href="Collection.html#optional-restrictions">optional</a>) 368 * @throws NullPointerException if this list contains a null element and the 369 * specified collection does not permit null elements 370 * (<a href="Collection.html#optional-restrictions">optional</a>), 371 * or if the specified collection is null 372 * @see #remove(Object) 373 * @see #contains(Object) 374 */ 375 boolean retainAll(Collection<?> c); 376 377 /** 378 * Removes all of the elements from this list (optional operation). 379 * The list will be empty after this call returns. 380 * 381 * @throws UnsupportedOperationException if the <tt>clear</tt> operation 382 * is not supported by this list 383 */ 384 void clear(); 385 386 387 // Comparison and hashing 388 389 /** 390 * Compares the specified object with this list for equality. Returns 391 * <tt>true</tt> if and only if the specified object is also a list, both 392 * lists have the same size, and all corresponding pairs of elements in 393 * the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and 394 * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null : 395 * e1.equals(e2))</tt>.) In other words, two lists are defined to be 396 * equal if they contain the same elements in the same order. This 397 * definition ensures that the equals method works properly across 398 * different implementations of the <tt>List</tt> interface. 399 * 400 * @param o the object to be compared for equality with this list 401 * @return <tt>true</tt> if the specified object is equal to this list 402 */ 403 boolean equals(Object o); 404 405 /** 406 * Returns the hash code value for this list. The hash code of a list 407 * is defined to be the result of the following calculation: 408 * <pre> 409 * int hashCode = 1; 410 * for (E e : list) 411 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode()); 412 * </pre> 413 * This ensures that <tt>list1.equals(list2)</tt> implies that 414 * <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists, 415 * <tt>list1</tt> and <tt>list2</tt>, as required by the general 416 * contract of {@link Object#hashCode}. 417 * 418 * @return the hash code value for this list 419 * @see Object#equals(Object) 420 * @see #equals(Object) 421 */ 422 int hashCode(); 423 424 425 // Positional Access Operations 426 427 /** 428 * Returns the element at the specified position in this list. 429 * 430 * @param index index of the element to return 431 * @return the element at the specified position in this list 432 * @throws IndexOutOfBoundsException if the index is out of range 433 * (<tt>index < 0 || index >= size()</tt>) 434 */ 435 E get(int index); 436 437 /** 438 * Replaces the element at the specified position in this list with the 439 * specified element (optional operation). 440 * 441 * @param index index of the element to replace 442 * @param element element to be stored at the specified position 443 * @return the element previously at the specified position 444 * @throws UnsupportedOperationException if the <tt>set</tt> operation 445 * is not supported by this list 446 * @throws ClassCastException if the class of the specified element 447 * prevents it from being added to this list 448 * @throws NullPointerException if the specified element is null and 449 * this list does not permit null elements 450 * @throws IllegalArgumentException if some property of the specified 451 * element prevents it from being added to this list 452 * @throws IndexOutOfBoundsException if the index is out of range 453 * (<tt>index < 0 || index >= size()</tt>) 454 */ 455 E set(int index, E element); 456 457 /** 458 * Inserts the specified element at the specified position in this list 459 * (optional operation). Shifts the element currently at that position 460 * (if any) and any subsequent elements to the right (adds one to their 461 * indices). 462 * 463 * @param index index at which the specified element is to be inserted 464 * @param element element to be inserted 465 * @throws UnsupportedOperationException if the <tt>add</tt> operation 466 * is not supported by this list 467 * @throws ClassCastException if the class of the specified element 468 * prevents it from being added to this list 469 * @throws NullPointerException if the specified element is null and 470 * this list does not permit null elements 471 * @throws IllegalArgumentException if some property of the specified 472 * element prevents it from being added to this list 473 * @throws IndexOutOfBoundsException if the index is out of range 474 * (<tt>index < 0 || index > size()</tt>) 475 */ 476 void add(int index, E element); 477 478 /** 479 * Removes the element at the specified position in this list (optional 480 * operation). Shifts any subsequent elements to the left (subtracts one 481 * from their indices). Returns the element that was removed from the 482 * list. 483 * 484 * @param index the index of the element to be removed 485 * @return the element previously at the specified position 486 * @throws UnsupportedOperationException if the <tt>remove</tt> operation 487 * is not supported by this list 488 * @throws IndexOutOfBoundsException if the index is out of range 489 * (<tt>index < 0 || index >= size()</tt>) 490 */ 491 E remove(int index); 492 493 494 // Search Operations 495 496 /** 497 * Returns the index of the first occurrence of the specified element 498 * in this list, or -1 if this list does not contain the element. 499 * More formally, returns the lowest index <tt>i</tt> such that 500 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 501 * or -1 if there is no such index. 502 * 503 * @param o element to search for 504 * @return the index of the first occurrence of the specified element in 505 * this list, or -1 if this list does not contain the element 506 * @throws ClassCastException if the type of the specified element 507 * is incompatible with this list 508 * (<a href="Collection.html#optional-restrictions">optional</a>) 509 * @throws NullPointerException if the specified element is null and this 510 * list does not permit null elements 511 * (<a href="Collection.html#optional-restrictions">optional</a>) 512 */ 513 int indexOf(Object o); 514 515 /** 516 * Returns the index of the last occurrence of the specified element 517 * in this list, or -1 if this list does not contain the element. 518 * More formally, returns the highest index <tt>i</tt> such that 519 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 520 * or -1 if there is no such index. 521 * 522 * @param o element to search for 523 * @return the index of the last occurrence of the specified element in 524 * this list, or -1 if this list does not contain the element 525 * @throws ClassCastException if the type of the specified element 526 * is incompatible with this list 527 * (<a href="Collection.html#optional-restrictions">optional</a>) 528 * @throws NullPointerException if the specified element is null and this 529 * list does not permit null elements 530 * (<a href="Collection.html#optional-restrictions">optional</a>) 531 */ 532 int lastIndexOf(Object o); 533 534 535 // List Iterators 536 537 /** 538 * Returns a list iterator over the elements in this list (in proper 539 * sequence). 540 * 541 * @return a list iterator over the elements in this list (in proper 542 * sequence) 543 */ 544 ListIterator<E> listIterator(); 545 546 /** 547 * Returns a list iterator over the elements in this list (in proper 548 * sequence), starting at the specified position in the list. 549 * The specified index indicates the first element that would be 550 * returned by an initial call to {@link ListIterator#next next}. 551 * An initial call to {@link ListIterator#previous previous} would 552 * return the element with the specified index minus one. 553 * 554 * @param index index of the first element to be returned from the 555 * list iterator (by a call to {@link ListIterator#next next}) 556 * @return a list iterator over the elements in this list (in proper 557 * sequence), starting at the specified position in the list 558 * @throws IndexOutOfBoundsException if the index is out of range 559 * ({@code index < 0 || index > size()}) 560 */ 561 ListIterator<E> listIterator(int index); 562 563 // View 564 565 /** 566 * Returns a view of the portion of this list between the specified 567 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If 568 * <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is 569 * empty.) The returned list is backed by this list, so non-structural 570 * changes in the returned list are reflected in this list, and vice-versa. 571 * The returned list supports all of the optional list operations supported 572 * by this list.<p> 573 * 574 * This method eliminates the need for explicit range operations (of 575 * the sort that commonly exist for arrays). Any operation that expects 576 * a list can be used as a range operation by passing a subList view 577 * instead of a whole list. For example, the following idiom 578 * removes a range of elements from a list: 579 * <pre> 580 * list.subList(from, to).clear(); 581 * </pre> 582 * Similar idioms may be constructed for <tt>indexOf</tt> and 583 * <tt>lastIndexOf</tt>, and all of the algorithms in the 584 * <tt>Collections</tt> class can be applied to a subList.<p> 585 * 586 * The semantics of the list returned by this method become undefined if 587 * the backing list (i.e., this list) is <i>structurally modified</i> in 588 * any way other than via the returned list. (Structural modifications are 589 * those that change the size of this list, or otherwise perturb it in such 590 * a fashion that iterations in progress may yield incorrect results.) 591 * 592 * @param fromIndex low endpoint (inclusive) of the subList 593 * @param toIndex high endpoint (exclusive) of the subList 594 * @return a view of the specified range within this list 595 * @throws IndexOutOfBoundsException for an illegal endpoint index value 596 * (<tt>fromIndex < 0 || toIndex > size || 597 * fromIndex > toIndex</tt>) 598 */ 599 List<E> subList(int fromIndex, int toIndex); 600} 601