1 /* 2 * Copyright (c) 1997, 2017, 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 26 package java.util; 27 28 import java.util.function.UnaryOperator; 29 30 /** 31 * An ordered collection (also known as a <i>sequence</i>). The user of this 32 * interface has precise control over where in the list each element is 33 * inserted. The user can access elements by their integer index (position in 34 * the list), and search for elements in the list.<p> 35 * 36 * Unlike sets, lists typically allow duplicate elements. More formally, 37 * lists typically allow pairs of elements {@code e1} and {@code e2} 38 * such that {@code e1.equals(e2)}, and they typically allow multiple 39 * null elements if they allow null elements at all. It is not inconceivable 40 * that someone might wish to implement a list that prohibits duplicates, by 41 * throwing runtime exceptions when the user attempts to insert them, but we 42 * expect this usage to be rare.<p> 43 * 44 * The {@code List} interface places additional stipulations, beyond those 45 * specified in the {@code Collection} interface, on the contracts of the 46 * {@code iterator}, {@code add}, {@code remove}, {@code equals}, and 47 * {@code hashCode} methods. Declarations for other inherited methods are 48 * also included here for convenience.<p> 49 * 50 * The {@code List} interface provides four methods for positional (indexed) 51 * access to list elements. Lists (like Java arrays) are zero based. Note 52 * that these operations may execute in time proportional to the index value 53 * for some implementations (the {@code LinkedList} class, for 54 * example). Thus, iterating over the elements in a list is typically 55 * preferable to indexing through it if the caller does not know the 56 * implementation.<p> 57 * 58 * The {@code List} interface provides a special iterator, called a 59 * {@code ListIterator}, that allows element insertion and replacement, and 60 * bidirectional access in addition to the normal operations that the 61 * {@code Iterator} interface provides. A method is provided to obtain a 62 * list iterator that starts at a specified position in the list.<p> 63 * 64 * The {@code List} interface provides two methods to search for a specified 65 * object. From a performance standpoint, these methods should be used with 66 * caution. In many implementations they will perform costly linear 67 * searches.<p> 68 * 69 * The {@code List} interface provides two methods to efficiently insert and 70 * remove multiple elements at an arbitrary point in the list.<p> 71 * 72 * Note: While it is permissible for lists to contain themselves as elements, 73 * extreme caution is advised: the {@code equals} and {@code hashCode} 74 * methods are no longer well defined on such a list. 75 * 76 * <p>Some list implementations have restrictions on the elements that 77 * they may contain. For example, some implementations prohibit null elements, 78 * and some have restrictions on the types of their elements. Attempting to 79 * add an ineligible element throws an unchecked exception, typically 80 * {@code NullPointerException} or {@code ClassCastException}. Attempting 81 * to query the presence of an ineligible element may throw an exception, 82 * or it may simply return false; some implementations will exhibit the former 83 * behavior and some will exhibit the latter. More generally, attempting an 84 * operation on an ineligible element whose completion would not result in 85 * the insertion of an ineligible element into the list may throw an 86 * exception or it may succeed, at the option of the implementation. 87 * Such exceptions are marked as "optional" in the specification for this 88 * interface. 89 * 90 * <h2><a id="unmodifiable">Unmodifiable Lists</a></h2> 91 * <p>The {@link List#of(Object...) List.of} and 92 * {@link List#copyOf List.copyOf} static factory methods 93 * provide a convenient way to create unmodifiable lists. The {@code List} 94 * instances created by these methods have the following characteristics: 95 * 96 * <ul> 97 * <li>They are <a href="Collection.html#unmodifiable"><i>unmodifiable</i></a>. Elements cannot 98 * be added, removed, or replaced. Calling any mutator method on the List 99 * will always cause {@code UnsupportedOperationException} to be thrown. 100 * However, if the contained elements are themselves mutable, 101 * this may cause the List's contents to appear to change. 102 * <li>They disallow {@code null} elements. Attempts to create them with 103 * {@code null} elements result in {@code NullPointerException}. 104 * <li>They are serializable if all elements are serializable. 105 * <li>The order of elements in the list is the same as the order of the 106 * provided arguments, or of the elements in the provided array. 107 * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>. 108 * Callers should make no assumptions about the identity of the returned instances. 109 * Factories are free to create new instances or reuse existing ones. Therefore, 110 * identity-sensitive operations on these instances (reference equality ({@code ==}), 111 * identity hash code, and synchronization) are unreliable and should be avoided. 112 * <li>They are serialized as specified on the 113 * <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a> 114 * page. 115 * </ul> 116 * 117 * <p>This interface is a member of the 118 * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework"> 119 * Java Collections Framework</a>. 120 * 121 * @param <E> the type of elements in this list 122 * 123 * @author Josh Bloch 124 * @author Neal Gafter 125 * @see Collection 126 * @see Set 127 * @see ArrayList 128 * @see LinkedList 129 * @see Vector 130 * @see Arrays#asList(Object[]) 131 * @see Collections#nCopies(int, Object) 132 * @see Collections#EMPTY_LIST 133 * @see AbstractList 134 * @see AbstractSequentialList 135 * @since 1.2 136 */ 137 138 public interface List<E> extends Collection<E> { 139 // Query Operations 140 141 /** 142 * Returns the number of elements in this list. If this list contains 143 * more than {@code Integer.MAX_VALUE} elements, returns 144 * {@code Integer.MAX_VALUE}. 145 * 146 * @return the number of elements in this list 147 */ 148 int size(); 149 150 /** 151 * Returns {@code true} if this list contains no elements. 152 * 153 * @return {@code true} if this list contains no elements 154 */ 155 boolean isEmpty(); 156 157 /** 158 * Returns {@code true} if this list contains the specified element. 159 * More formally, returns {@code true} if and only if this list contains 160 * at least one element {@code e} such that 161 * {@code Objects.equals(o, e)}. 162 * 163 * @param o element whose presence in this list is to be tested 164 * @return {@code true} if this list contains the specified element 165 * @throws ClassCastException if the type of the specified element 166 * is incompatible with this list 167 * (<a href="Collection.html#optional-restrictions">optional</a>) 168 * @throws NullPointerException if the specified element is null and this 169 * list does not permit null elements 170 * (<a href="Collection.html#optional-restrictions">optional</a>) 171 */ 172 boolean contains(Object o); 173 174 /** 175 * Returns an iterator over the elements in this list in proper sequence. 176 * 177 * @return an iterator over the elements in this list in proper sequence 178 */ 179 Iterator<E> iterator(); 180 181 /** 182 * Returns an array containing all of the elements in this list in proper 183 * sequence (from first to last element). 184 * 185 * <p>The returned array will be "safe" in that no references to it are 186 * maintained by this list. (In other words, this method must 187 * allocate a new array even if this list is backed by an array). 188 * The caller is thus free to modify the returned array. 189 * 190 * <p>This method acts as bridge between array-based and collection-based 191 * APIs. 192 * 193 * @return an array containing all of the elements in this list in proper 194 * sequence 195 * @see Arrays#asList(Object[]) 196 */ 197 Object[] toArray(); 198 199 /** 200 * Returns an array containing all of the elements in this list in 201 * proper sequence (from first to last element); the runtime type of 202 * the returned array is that of the specified array. If the list fits 203 * in the specified array, it is returned therein. Otherwise, a new 204 * array is allocated with the runtime type of the specified array and 205 * the size of this list. 206 * 207 * <p>If the list fits in the specified array with room to spare (i.e., 208 * the array has more elements than the list), the element in the array 209 * immediately following the end of the list is set to {@code null}. 210 * (This is useful in determining the length of the list <i>only</i> if 211 * the caller knows that the list does not contain any null elements.) 212 * 213 * <p>Like the {@link #toArray()} method, this method acts as bridge between 214 * array-based and collection-based APIs. Further, this method allows 215 * precise control over the runtime type of the output array, and may, 216 * under certain circumstances, be used to save allocation costs. 217 * 218 * <p>Suppose {@code x} is a list known to contain only strings. 219 * The following code can be used to dump the list into a newly 220 * allocated array of {@code String}: 221 * 222 * <pre>{@code 223 * String[] y = x.toArray(new String[0]); 224 * }</pre> 225 * 226 * Note that {@code toArray(new Object[0])} is identical in function to 227 * {@code toArray()}. 228 * 229 * @param a the array into which the elements of this list are to 230 * be stored, if it is big enough; otherwise, a new array of the 231 * same runtime type is allocated for this purpose. 232 * @return an array containing the elements of this list 233 * @throws ArrayStoreException if the runtime type of the specified array 234 * is not a supertype of the runtime type of every element in 235 * this list 236 * @throws NullPointerException if the specified array is null 237 */ 238 <T> T[] toArray(T[] a); 239 240 241 // Modification Operations 242 243 /** 244 * Appends the specified element to the end of this list (optional 245 * operation). 246 * 247 * <p>Lists that support this operation may place limitations on what 248 * elements may be added to this list. In particular, some 249 * lists will refuse to add null elements, and others will impose 250 * restrictions on the type of elements that may be added. List 251 * classes should clearly specify in their documentation any restrictions 252 * on what elements may be added. 253 * 254 * @param e element to be appended to this list 255 * @return {@code true} (as specified by {@link Collection#add}) 256 * @throws UnsupportedOperationException if the {@code add} operation 257 * is not supported by this list 258 * @throws ClassCastException if the class of the specified element 259 * prevents it from being added to this list 260 * @throws NullPointerException if the specified element is null and this 261 * list does not permit null elements 262 * @throws IllegalArgumentException if some property of this element 263 * prevents it from being added to this list 264 */ 265 boolean add(E e); 266 267 /** 268 * Removes the first occurrence of the specified element from this list, 269 * if it is present (optional operation). If this list does not contain 270 * the element, it is unchanged. More formally, removes the element with 271 * the lowest index {@code i} such that 272 * {@code Objects.equals(o, get(i))} 273 * (if such an element exists). Returns {@code true} if this list 274 * contained the specified element (or equivalently, if this list changed 275 * as a result of the call). 276 * 277 * @param o element to be removed from this list, if present 278 * @return {@code true} if this list contained the specified element 279 * @throws ClassCastException if the type of the specified element 280 * is incompatible with this list 281 * (<a href="Collection.html#optional-restrictions">optional</a>) 282 * @throws NullPointerException if the specified element is null and this 283 * list does not permit null elements 284 * (<a href="Collection.html#optional-restrictions">optional</a>) 285 * @throws UnsupportedOperationException if the {@code remove} operation 286 * is not supported by this list 287 */ 288 boolean remove(Object o); 289 290 291 // Bulk Modification Operations 292 293 /** 294 * Returns {@code true} if this list contains all of the elements of the 295 * specified collection. 296 * 297 * @param c collection to be checked for containment in this list 298 * @return {@code true} if this list contains all of the elements of the 299 * specified collection 300 * @throws ClassCastException if the types of one or more elements 301 * in the specified collection are incompatible with this 302 * list 303 * (<a href="Collection.html#optional-restrictions">optional</a>) 304 * @throws NullPointerException if the specified collection contains one 305 * or more null elements and this list does not permit null 306 * elements 307 * (<a href="Collection.html#optional-restrictions">optional</a>), 308 * or if the specified collection is null 309 * @see #contains(Object) 310 */ 311 boolean containsAll(Collection<?> c); 312 313 /** 314 * Appends all of the elements in the specified collection to the end of 315 * this list, in the order that they are returned by the specified 316 * collection's iterator (optional operation). The behavior of this 317 * operation is undefined if the specified collection is modified while 318 * the operation is in progress. (Note that this will occur if the 319 * specified collection is this list, and it's nonempty.) 320 * 321 * @param c collection containing elements to be added to this list 322 * @return {@code true} if this list changed as a result of the call 323 * @throws UnsupportedOperationException if the {@code addAll} operation 324 * is not supported by this list 325 * @throws ClassCastException if the class of an element of the specified 326 * collection prevents it from being added to this list 327 * @throws NullPointerException if the specified collection contains one 328 * or more null elements and this list does not permit null 329 * elements, or if the specified collection is null 330 * @throws IllegalArgumentException if some property of an element of the 331 * specified collection prevents it from being added to this list 332 * @see #add(Object) 333 */ 334 boolean addAll(Collection<? extends E> c); 335 336 /** 337 * Inserts all of the elements in the specified collection into this 338 * list at the specified position (optional operation). Shifts the 339 * element currently at that position (if any) and any subsequent 340 * elements to the right (increases their indices). The new elements 341 * will appear in this list in the order that they are returned by the 342 * specified collection's iterator. The behavior of this operation is 343 * undefined if the specified collection is modified while the 344 * operation is in progress. (Note that this will occur if the specified 345 * collection is this list, and it's nonempty.) 346 * 347 * @param index index at which to insert the first element from the 348 * specified collection 349 * @param c collection containing elements to be added to this list 350 * @return {@code true} if this list changed as a result of the call 351 * @throws UnsupportedOperationException if the {@code addAll} operation 352 * is not supported by this list 353 * @throws ClassCastException if the class of an element of the specified 354 * collection prevents it from being added to this list 355 * @throws NullPointerException if the specified collection contains one 356 * or more null elements and this list does not permit null 357 * elements, or if the specified collection is null 358 * @throws IllegalArgumentException if some property of an element of the 359 * specified collection prevents it from being added to this list 360 * @throws IndexOutOfBoundsException if the index is out of range 361 * ({@code index < 0 || index > size()}) 362 */ 363 boolean addAll(int index, Collection<? extends E> c); 364 365 /** 366 * Removes from this list all of its elements that are contained in the 367 * specified collection (optional operation). 368 * 369 * @param c collection containing elements to be removed from this list 370 * @return {@code true} if this list changed as a result of the call 371 * @throws UnsupportedOperationException if the {@code removeAll} operation 372 * is not supported by this list 373 * @throws ClassCastException if the class of an element of this list 374 * is incompatible with the specified collection 375 * (<a href="Collection.html#optional-restrictions">optional</a>) 376 * @throws NullPointerException if this list contains a null element and the 377 * specified collection does not permit null elements 378 * (<a href="Collection.html#optional-restrictions">optional</a>), 379 * or if the specified collection is null 380 * @see #remove(Object) 381 * @see #contains(Object) 382 */ 383 boolean removeAll(Collection<?> c); 384 385 /** 386 * Retains only the elements in this list that are contained in the 387 * specified collection (optional operation). In other words, removes 388 * from this list all of its elements that are not contained in the 389 * specified collection. 390 * 391 * @param c collection containing elements to be retained in this list 392 * @return {@code true} if this list changed as a result of the call 393 * @throws UnsupportedOperationException if the {@code retainAll} operation 394 * is not supported by this list 395 * @throws ClassCastException if the class of an element of this list 396 * is incompatible with the specified collection 397 * (<a href="Collection.html#optional-restrictions">optional</a>) 398 * @throws NullPointerException if this list contains a null element and the 399 * specified collection does not permit null elements 400 * (<a href="Collection.html#optional-restrictions">optional</a>), 401 * or if the specified collection is null 402 * @see #remove(Object) 403 * @see #contains(Object) 404 */ 405 boolean retainAll(Collection<?> c); 406 407 /** 408 * Replaces each element of this list with the result of applying the 409 * operator to that element. Errors or runtime exceptions thrown by 410 * the operator are relayed to the caller. 411 * 412 * @implSpec 413 * The default implementation is equivalent to, for this {@code list}: 414 * <pre>{@code 415 * final ListIterator<E> li = list.listIterator(); 416 * while (li.hasNext()) { 417 * li.set(operator.apply(li.next())); 418 * } 419 * }</pre> 420 * 421 * If the list's list-iterator does not support the {@code set} operation 422 * then an {@code UnsupportedOperationException} will be thrown when 423 * replacing the first element. 424 * 425 * @param operator the operator to apply to each element 426 * @throws UnsupportedOperationException if this list is unmodifiable. 427 * Implementations may throw this exception if an element 428 * cannot be replaced or if, in general, modification is not 429 * supported 430 * @throws NullPointerException if the specified operator is null or 431 * if the operator result is a null value and this list does 432 * not permit null elements 433 * (<a href="Collection.html#optional-restrictions">optional</a>) 434 * @since 1.8 435 */ 436 default void replaceAll(UnaryOperator<E> operator) { 437 Objects.requireNonNull(operator); 438 final ListIterator<E> li = this.listIterator(); 439 while (li.hasNext()) { 440 li.set(operator.apply(li.next())); 441 } 442 } 443 444 /** 445 * Sorts this list according to the order induced by the specified 446 * {@link Comparator}. The sort is <i>stable</i>: this method must not 447 * reorder equal elements. 448 * 449 * <p>All elements in this list must be <i>mutually comparable</i> using the 450 * specified comparator (that is, {@code c.compare(e1, e2)} must not throw 451 * a {@code ClassCastException} for any elements {@code e1} and {@code e2} 452 * in the list). 453 * 454 * <p>If the specified comparator is {@code null} then all elements in this 455 * list must implement the {@link Comparable} interface and the elements' 456 * {@linkplain Comparable natural ordering} should be used. 457 * 458 * <p>This list must be modifiable, but need not be resizable. 459 * 460 * @implSpec 461 * The default implementation obtains an array containing all elements in 462 * this list, sorts the array, and iterates over this list resetting each 463 * element from the corresponding position in the array. (This avoids the 464 * n<sup>2</sup> log(n) performance that would result from attempting 465 * to sort a linked list in place.) 466 * 467 * @implNote 468 * This implementation is a stable, adaptive, iterative mergesort that 469 * requires far fewer than n lg(n) comparisons when the input array is 470 * partially sorted, while offering the performance of a traditional 471 * mergesort when the input array is randomly ordered. If the input array 472 * is nearly sorted, the implementation requires approximately n 473 * comparisons. Temporary storage requirements vary from a small constant 474 * for nearly sorted input arrays to n/2 object references for randomly 475 * ordered input arrays. 476 * 477 * <p>The implementation takes equal advantage of ascending and 478 * descending order in its input array, and can take advantage of 479 * ascending and descending order in different parts of the same 480 * input array. It is well-suited to merging two or more sorted arrays: 481 * simply concatenate the arrays and sort the resulting array. 482 * 483 * <p>The implementation was adapted from Tim Peters's list sort for Python 484 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 485 * TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic 486 * Sorting and Information Theoretic Complexity", in Proceedings of the 487 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 488 * January 1993. 489 * 490 * @param c the {@code Comparator} used to compare list elements. 491 * A {@code null} value indicates that the elements' 492 * {@linkplain Comparable natural ordering} should be used 493 * @throws ClassCastException if the list contains elements that are not 494 * <i>mutually comparable</i> using the specified comparator 495 * @throws UnsupportedOperationException if the list's list-iterator does 496 * not support the {@code set} operation 497 * @throws IllegalArgumentException 498 * (<a href="Collection.html#optional-restrictions">optional</a>) 499 * if the comparator is found to violate the {@link Comparator} 500 * contract 501 * @since 1.8 502 */ 503 @SuppressWarnings({"unchecked", "rawtypes"}) 504 default void sort(Comparator<? super E> c) { 505 Object[] a = this.toArray(); 506 Arrays.sort(a, (Comparator) c); 507 ListIterator<E> i = this.listIterator(); 508 for (Object e : a) { 509 i.next(); 510 i.set((E) e); 511 } 512 } 513 514 /** 515 * Removes all of the elements from this list (optional operation). 516 * The list will be empty after this call returns. 517 * 518 * @throws UnsupportedOperationException if the {@code clear} operation 519 * is not supported by this list 520 */ 521 void clear(); 522 523 524 // Comparison and hashing 525 526 /** 527 * Compares the specified object with this list for equality. Returns 528 * {@code true} if and only if the specified object is also a list, both 529 * lists have the same size, and all corresponding pairs of elements in 530 * the two lists are <i>equal</i>. (Two elements {@code e1} and 531 * {@code e2} are <i>equal</i> if {@code Objects.equals(e1, e2)}.) 532 * In other words, two lists are defined to be 533 * equal if they contain the same elements in the same order. This 534 * definition ensures that the equals method works properly across 535 * different implementations of the {@code List} interface. 536 * 537 * @param o the object to be compared for equality with this list 538 * @return {@code true} if the specified object is equal to this list 539 */ 540 boolean equals(Object o); 541 542 /** 543 * Returns the hash code value for this list. The hash code of a list 544 * is defined to be the result of the following calculation: 545 * <pre>{@code 546 * int hashCode = 1; 547 * for (E e : list) 548 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode()); 549 * }</pre> 550 * This ensures that {@code list1.equals(list2)} implies that 551 * {@code list1.hashCode()==list2.hashCode()} for any two lists, 552 * {@code list1} and {@code list2}, as required by the general 553 * contract of {@link Object#hashCode}. 554 * 555 * @return the hash code value for this list 556 * @see Object#equals(Object) 557 * @see #equals(Object) 558 */ 559 int hashCode(); 560 561 562 // Positional Access Operations 563 564 /** 565 * Returns the element at the specified position in this list. 566 * 567 * @param index index of the element to return 568 * @return the element at the specified position in this list 569 * @throws IndexOutOfBoundsException if the index is out of range 570 * ({@code index < 0 || index >= size()}) 571 */ 572 E get(int index); 573 574 /** 575 * Replaces the element at the specified position in this list with the 576 * specified element (optional operation). 577 * 578 * @param index index of the element to replace 579 * @param element element to be stored at the specified position 580 * @return the element previously at the specified position 581 * @throws UnsupportedOperationException if the {@code set} operation 582 * is not supported by this list 583 * @throws ClassCastException if the class of the specified element 584 * prevents it from being added to this list 585 * @throws NullPointerException if the specified element is null and 586 * this list does not permit null elements 587 * @throws IllegalArgumentException if some property of the specified 588 * element prevents it from being added to this list 589 * @throws IndexOutOfBoundsException if the index is out of range 590 * ({@code index < 0 || index >= size()}) 591 */ 592 E set(int index, E element); 593 594 /** 595 * Inserts the specified element at the specified position in this list 596 * (optional operation). Shifts the element currently at that position 597 * (if any) and any subsequent elements to the right (adds one to their 598 * indices). 599 * 600 * @param index index at which the specified element is to be inserted 601 * @param element element to be inserted 602 * @throws UnsupportedOperationException if the {@code add} operation 603 * is not supported by this list 604 * @throws ClassCastException if the class of the specified element 605 * prevents it from being added to this list 606 * @throws NullPointerException if the specified element is null and 607 * this list does not permit null elements 608 * @throws IllegalArgumentException if some property of the specified 609 * element prevents it from being added to this list 610 * @throws IndexOutOfBoundsException if the index is out of range 611 * ({@code index < 0 || index > size()}) 612 */ 613 void add(int index, E element); 614 615 /** 616 * Removes the element at the specified position in this list (optional 617 * operation). Shifts any subsequent elements to the left (subtracts one 618 * from their indices). Returns the element that was removed from the 619 * list. 620 * 621 * @param index the index of the element to be removed 622 * @return the element previously at the specified position 623 * @throws UnsupportedOperationException if the {@code remove} operation 624 * is not supported by this list 625 * @throws IndexOutOfBoundsException if the index is out of range 626 * ({@code index < 0 || index >= size()}) 627 */ 628 E remove(int index); 629 630 631 // Search Operations 632 633 /** 634 * Returns the index of the first occurrence of the specified element 635 * in this list, or -1 if this list does not contain the element. 636 * More formally, returns the lowest index {@code i} such that 637 * {@code Objects.equals(o, get(i))}, 638 * or -1 if there is no such index. 639 * 640 * @param o element to search for 641 * @return the index of the first occurrence of the specified element in 642 * this list, or -1 if this list does not contain the element 643 * @throws ClassCastException if the type of the specified element 644 * is incompatible with this list 645 * (<a href="Collection.html#optional-restrictions">optional</a>) 646 * @throws NullPointerException if the specified element is null and this 647 * list does not permit null elements 648 * (<a href="Collection.html#optional-restrictions">optional</a>) 649 */ 650 int indexOf(Object o); 651 652 /** 653 * Returns the index of the last occurrence of the specified element 654 * in this list, or -1 if this list does not contain the element. 655 * More formally, returns the highest index {@code i} such that 656 * {@code Objects.equals(o, get(i))}, 657 * or -1 if there is no such index. 658 * 659 * @param o element to search for 660 * @return the index of the last occurrence of the specified element in 661 * this list, or -1 if this list does not contain the element 662 * @throws ClassCastException if the type of the specified element 663 * is incompatible with this list 664 * (<a href="Collection.html#optional-restrictions">optional</a>) 665 * @throws NullPointerException if the specified element is null and this 666 * list does not permit null elements 667 * (<a href="Collection.html#optional-restrictions">optional</a>) 668 */ 669 int lastIndexOf(Object o); 670 671 672 // List Iterators 673 674 /** 675 * Returns a list iterator over the elements in this list (in proper 676 * sequence). 677 * 678 * @return a list iterator over the elements in this list (in proper 679 * sequence) 680 */ 681 ListIterator<E> listIterator(); 682 683 /** 684 * Returns a list iterator over the elements in this list (in proper 685 * sequence), starting at the specified position in the list. 686 * The specified index indicates the first element that would be 687 * returned by an initial call to {@link ListIterator#next next}. 688 * An initial call to {@link ListIterator#previous previous} would 689 * return the element with the specified index minus one. 690 * 691 * @param index index of the first element to be returned from the 692 * list iterator (by a call to {@link ListIterator#next next}) 693 * @return a list iterator over the elements in this list (in proper 694 * sequence), starting at the specified position in the list 695 * @throws IndexOutOfBoundsException if the index is out of range 696 * ({@code index < 0 || index > size()}) 697 */ 698 ListIterator<E> listIterator(int index); 699 700 // View 701 702 /** 703 * Returns a view of the portion of this list between the specified 704 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If 705 * {@code fromIndex} and {@code toIndex} are equal, the returned list is 706 * empty.) The returned list is backed by this list, so non-structural 707 * changes in the returned list are reflected in this list, and vice-versa. 708 * The returned list supports all of the optional list operations supported 709 * by this list.<p> 710 * 711 * This method eliminates the need for explicit range operations (of 712 * the sort that commonly exist for arrays). Any operation that expects 713 * a list can be used as a range operation by passing a subList view 714 * instead of a whole list. For example, the following idiom 715 * removes a range of elements from a list: 716 * <pre>{@code 717 * list.subList(from, to).clear(); 718 * }</pre> 719 * Similar idioms may be constructed for {@code indexOf} and 720 * {@code lastIndexOf}, and all of the algorithms in the 721 * {@code Collections} class can be applied to a subList.<p> 722 * 723 * The semantics of the list returned by this method become undefined if 724 * the backing list (i.e., this list) is <i>structurally modified</i> in 725 * any way other than via the returned list. (Structural modifications are 726 * those that change the size of this list, or otherwise perturb it in such 727 * a fashion that iterations in progress may yield incorrect results.) 728 * 729 * @param fromIndex low endpoint (inclusive) of the subList 730 * @param toIndex high endpoint (exclusive) of the subList 731 * @return a view of the specified range within this list 732 * @throws IndexOutOfBoundsException for an illegal endpoint index value 733 * ({@code fromIndex < 0 || toIndex > size || 734 * fromIndex > toIndex}) 735 */ 736 List<E> subList(int fromIndex, int toIndex); 737 738 /** 739 * Creates a {@link Spliterator} over the elements in this list. 740 * 741 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and 742 * {@link Spliterator#ORDERED}. Implementations should document the 743 * reporting of additional characteristic values. 744 * 745 * @implSpec 746 * The default implementation creates a 747 * <em><a href="Spliterator.html#binding">late-binding</a></em> 748 * spliterator as follows: 749 * <ul> 750 * <li>If the list is an instance of {@link RandomAccess} then the default 751 * implementation creates a spliterator that traverses elements by 752 * invoking the method {@link List#get}. If such invocation results or 753 * would result in an {@code IndexOutOfBoundsException} then the 754 * spliterator will <em>fail-fast</em> and throw a 755 * {@code ConcurrentModificationException}. 756 * If the list is also an instance of {@link AbstractList} then the 757 * spliterator will use the list's {@link AbstractList#modCount modCount} 758 * field to provide additional <em>fail-fast</em> behavior. 759 * <li>Otherwise, the default implementation creates a spliterator from the 760 * list's {@code Iterator}. The spliterator inherits the 761 * <em>fail-fast</em> of the list's iterator. 762 * </ul> 763 * 764 * @implNote 765 * The created {@code Spliterator} additionally reports 766 * {@link Spliterator#SUBSIZED}. 767 * 768 * @return a {@code Spliterator} over the elements in this list 769 * @since 1.8 770 */ 771 @Override 772 default Spliterator<E> spliterator() { 773 if (this instanceof RandomAccess) { 774 return new AbstractList.RandomAccessSpliterator<>(this); 775 } else { 776 return Spliterators.spliterator(this, Spliterator.ORDERED); 777 } 778 } 779 780 /** 781 * Returns an unmodifiable list containing zero elements. 782 * 783 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 784 * 785 * @param <E> the {@code List}'s element type 786 * @return an empty {@code List} 787 * 788 * @since 9 789 */ 790 static <E> List<E> of() { 791 return ImmutableCollections.emptyList(); 792 } 793 794 /** 795 * Returns an unmodifiable list containing one element. 796 * 797 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 798 * 799 * @param <E> the {@code List}'s element type 800 * @param e1 the single element 801 * @return a {@code List} containing the specified element 802 * @throws NullPointerException if the element is {@code null} 803 * 804 * @since 9 805 */ 806 static <E> List<E> of(E e1) { 807 return new ImmutableCollections.List12<>(e1); 808 } 809 810 /** 811 * Returns an unmodifiable list containing two elements. 812 * 813 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 814 * 815 * @param <E> the {@code List}'s element type 816 * @param e1 the first element 817 * @param e2 the second element 818 * @return a {@code List} containing the specified elements 819 * @throws NullPointerException if an element is {@code null} 820 * 821 * @since 9 822 */ 823 static <E> List<E> of(E e1, E e2) { 824 return new ImmutableCollections.List12<>(e1, e2); 825 } 826 827 /** 828 * Returns an unmodifiable list containing three elements. 829 * 830 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 831 * 832 * @param <E> the {@code List}'s element type 833 * @param e1 the first element 834 * @param e2 the second element 835 * @param e3 the third element 836 * @return a {@code List} containing the specified elements 837 * @throws NullPointerException if an element is {@code null} 838 * 839 * @since 9 840 */ 841 static <E> List<E> of(E e1, E e2, E e3) { 842 return new ImmutableCollections.ListN<>(e1, e2, e3); 843 } 844 845 /** 846 * Returns an unmodifiable list containing four elements. 847 * 848 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 849 * 850 * @param <E> the {@code List}'s element type 851 * @param e1 the first element 852 * @param e2 the second element 853 * @param e3 the third element 854 * @param e4 the fourth element 855 * @return a {@code List} containing the specified elements 856 * @throws NullPointerException if an element is {@code null} 857 * 858 * @since 9 859 */ 860 static <E> List<E> of(E e1, E e2, E e3, E e4) { 861 return new ImmutableCollections.ListN<>(e1, e2, e3, e4); 862 } 863 864 /** 865 * Returns an unmodifiable list containing five elements. 866 * 867 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 868 * 869 * @param <E> the {@code List}'s element type 870 * @param e1 the first element 871 * @param e2 the second element 872 * @param e3 the third element 873 * @param e4 the fourth element 874 * @param e5 the fifth element 875 * @return a {@code List} containing the specified elements 876 * @throws NullPointerException if an element is {@code null} 877 * 878 * @since 9 879 */ 880 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5) { 881 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5); 882 } 883 884 /** 885 * Returns an unmodifiable list containing six elements. 886 * 887 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 888 * 889 * @param <E> the {@code List}'s element type 890 * @param e1 the first element 891 * @param e2 the second element 892 * @param e3 the third element 893 * @param e4 the fourth element 894 * @param e5 the fifth element 895 * @param e6 the sixth element 896 * @return a {@code List} containing the specified elements 897 * @throws NullPointerException if an element is {@code null} 898 * 899 * @since 9 900 */ 901 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6) { 902 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 903 e6); 904 } 905 906 /** 907 * Returns an unmodifiable list containing seven elements. 908 * 909 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 910 * 911 * @param <E> the {@code List}'s element type 912 * @param e1 the first element 913 * @param e2 the second element 914 * @param e3 the third element 915 * @param e4 the fourth element 916 * @param e5 the fifth element 917 * @param e6 the sixth element 918 * @param e7 the seventh element 919 * @return a {@code List} containing the specified elements 920 * @throws NullPointerException if an element is {@code null} 921 * 922 * @since 9 923 */ 924 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) { 925 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 926 e6, e7); 927 } 928 929 /** 930 * Returns an unmodifiable list containing eight elements. 931 * 932 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 933 * 934 * @param <E> the {@code List}'s element type 935 * @param e1 the first element 936 * @param e2 the second element 937 * @param e3 the third element 938 * @param e4 the fourth element 939 * @param e5 the fifth element 940 * @param e6 the sixth element 941 * @param e7 the seventh element 942 * @param e8 the eighth element 943 * @return a {@code List} containing the specified elements 944 * @throws NullPointerException if an element is {@code null} 945 * 946 * @since 9 947 */ 948 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) { 949 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 950 e6, e7, e8); 951 } 952 953 /** 954 * Returns an unmodifiable list containing nine elements. 955 * 956 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 957 * 958 * @param <E> the {@code List}'s element type 959 * @param e1 the first element 960 * @param e2 the second element 961 * @param e3 the third element 962 * @param e4 the fourth element 963 * @param e5 the fifth element 964 * @param e6 the sixth element 965 * @param e7 the seventh element 966 * @param e8 the eighth element 967 * @param e9 the ninth element 968 * @return a {@code List} containing the specified elements 969 * @throws NullPointerException if an element is {@code null} 970 * 971 * @since 9 972 */ 973 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) { 974 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 975 e6, e7, e8, e9); 976 } 977 978 /** 979 * Returns an unmodifiable list containing ten elements. 980 * 981 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 982 * 983 * @param <E> the {@code List}'s element type 984 * @param e1 the first element 985 * @param e2 the second element 986 * @param e3 the third element 987 * @param e4 the fourth element 988 * @param e5 the fifth element 989 * @param e6 the sixth element 990 * @param e7 the seventh element 991 * @param e8 the eighth element 992 * @param e9 the ninth element 993 * @param e10 the tenth element 994 * @return a {@code List} containing the specified elements 995 * @throws NullPointerException if an element is {@code null} 996 * 997 * @since 9 998 */ 999 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) { 1000 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 1001 e6, e7, e8, e9, e10); 1002 } 1003 1004 /** 1005 * Returns an unmodifiable list containing an arbitrary number of elements. 1006 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 1007 * 1008 * @apiNote 1009 * This method also accepts a single array as an argument. The element type of 1010 * the resulting list will be the component type of the array, and the size of 1011 * the list will be equal to the length of the array. To create a list with 1012 * a single element that is an array, do the following: 1013 * 1014 * <pre>{@code 1015 * String[] array = ... ; 1016 * List<String[]> list = List.<String[]>of(array); 1017 * }</pre> 1018 * 1019 * This will cause the {@link List#of(Object) List.of(E)} method 1020 * to be invoked instead. 1021 * 1022 * @param <E> the {@code List}'s element type 1023 * @param elements the elements to be contained in the list 1024 * @return a {@code List} containing the specified elements 1025 * @throws NullPointerException if an element is {@code null} or if the array is {@code null} 1026 * 1027 * @since 9 1028 */ 1029 @SafeVarargs 1030 @SuppressWarnings("varargs") 1031 static <E> List<E> of(E... elements) { 1032 switch (elements.length) { // implicit null check of elements 1033 case 0: 1034 return ImmutableCollections.emptyList(); 1035 case 1: 1036 return new ImmutableCollections.List12<>(elements[0]); 1037 case 2: 1038 return new ImmutableCollections.List12<>(elements[0], elements[1]); 1039 default: 1040 return new ImmutableCollections.ListN<>(elements); 1041 } 1042 } 1043 1044 /** 1045 * Returns an <a href="#unmodifiable">unmodifiable List</a> containing the elements of 1046 * the given Collection, in its iteration order. The given Collection must not be null, 1047 * and it must not contain any null elements. If the given Collection is subsequently 1048 * modified, the returned List will not reflect such modifications. 1049 * 1050 * @implNote 1051 * If the given Collection is an <a href="#unmodifiable">unmodifiable List</a>, 1052 * calling copyOf will generally not create a copy. 1053 * 1054 * @param <E> the {@code List}'s element type 1055 * @param coll a {@code Collection} from which elements are drawn, must be non-null 1056 * @return a {@code List} containing the elements of the given {@code Collection} 1057 * @throws NullPointerException if coll is null, or if it contains any nulls 1058 * @since 10 1059 */ 1060 @SuppressWarnings("unchecked") 1061 static <E> List<E> copyOf(Collection<? extends E> coll) { 1062 if (coll instanceof ImmutableCollections.AbstractImmutableList) { 1063 return (List<E>)coll; 1064 } else { 1065 return (List<E>)List.of(coll.toArray()); 1066 } 1067 } 1068 }