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 26package java.util; 27 28import 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="immutable">Immutable List Static Factory Methods</a></h2> 91 * <p>The {@link List#of(Object...) List.of()} static factory methods 92 * provide a convenient way to create immutable lists. The {@code List} 93 * instances created by these methods have the following characteristics: 94 * 95 * <ul> 96 * <li>They are <em>structurally immutable</em>. Elements cannot be added, removed, 97 * or replaced. Calling any mutator method will always cause 98 * {@code UnsupportedOperationException} to be thrown. 99 * However, if the contained elements are themselves mutable, 100 * this may cause the List's contents to appear to change. 101 * <li>They disallow {@code null} elements. Attempts to create them with 102 * {@code null} elements result in {@code NullPointerException}. 103 * <li>They are serializable if all elements are serializable. 104 * <li>The order of elements in the list is the same as the order of the 105 * provided arguments, or of the elements in the provided array. 106 * <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>. 107 * Callers should make no assumptions about the identity of the returned instances. 108 * Factories are free to create new instances or reuse existing ones. Therefore, 109 * identity-sensitive operations on these instances (reference equality ({@code ==}), 110 * identity hash code, and synchronization) are unreliable and should be avoided. 111 * <li>They are serialized as specified on the 112 * <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a> 113 * page. 114 * </ul> 115 * 116 * <p>This interface is a member of the 117 * <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework"> 118 * Java Collections Framework</a>. 119 * 120 * @param <E> the type of elements in this list 121 * 122 * @author Josh Bloch 123 * @author Neal Gafter 124 * @see Collection 125 * @see Set 126 * @see ArrayList 127 * @see LinkedList 128 * @see Vector 129 * @see Arrays#asList(Object[]) 130 * @see Collections#nCopies(int, Object) 131 * @see Collections#EMPTY_LIST 132 * @see AbstractList 133 * @see AbstractSequentialList 134 * @since 1.2 135 */ 136 137public interface List<E> extends Collection<E> { 138 // Query Operations 139 140 /** 141 * Returns the number of elements in this list. If this list contains 142 * more than {@code Integer.MAX_VALUE} elements, returns 143 * {@code Integer.MAX_VALUE}. 144 * 145 * @return the number of elements in this list 146 */ 147 int size(); 148 149 /** 150 * Returns {@code true} if this list contains no elements. 151 * 152 * @return {@code true} if this list contains no elements 153 */ 154 boolean isEmpty(); 155 156 /** 157 * Returns {@code true} if this list contains the specified element. 158 * More formally, returns {@code true} if and only if this list contains 159 * at least one element {@code e} such that 160 * {@code Objects.equals(o, e)}. 161 * 162 * @param o element whose presence in this list is to be tested 163 * @return {@code true} if this list contains the specified element 164 * @throws ClassCastException if the type of the specified element 165 * is incompatible with this list 166 * (<a href="Collection.html#optional-restrictions">optional</a>) 167 * @throws NullPointerException if the specified element is null and this 168 * list does not permit null elements 169 * (<a href="Collection.html#optional-restrictions">optional</a>) 170 */ 171 boolean contains(Object o); 172 173 /** 174 * Returns an iterator over the elements in this list in proper sequence. 175 * 176 * @return an iterator over the elements in this list in proper sequence 177 */ 178 Iterator<E> iterator(); 179 180 /** 181 * Returns an array containing all of the elements in this list in proper 182 * sequence (from first to last element). 183 * 184 * <p>The returned array will be "safe" in that no references to it are 185 * maintained by this list. (In other words, this method must 186 * allocate a new array even if this list is backed by an array). 187 * The caller is thus free to modify the returned array. 188 * 189 * <p>This method acts as bridge between array-based and collection-based 190 * APIs. 191 * 192 * @return an array containing all of the elements in this list in proper 193 * sequence 194 * @see Arrays#asList(Object[]) 195 */ 196 Object[] toArray(); 197 198 /** 199 * Returns an array containing all of the elements in this list in 200 * proper sequence (from first to last element); the runtime type of 201 * the returned array is that of the specified array. If the list fits 202 * in the specified array, it is returned therein. Otherwise, a new 203 * array is allocated with the runtime type of the specified array and 204 * the size of this list. 205 * 206 * <p>If the list fits in the specified array with room to spare (i.e., 207 * the array has more elements than the list), the element in the array 208 * immediately following the end of the list is set to {@code null}. 209 * (This is useful in determining the length of the list <i>only</i> if 210 * the caller knows that the list does not contain any null elements.) 211 * 212 * <p>Like the {@link #toArray()} method, this method acts as bridge between 213 * array-based and collection-based APIs. Further, this method allows 214 * precise control over the runtime type of the output array, and may, 215 * under certain circumstances, be used to save allocation costs. 216 * 217 * <p>Suppose {@code x} is a list known to contain only strings. 218 * The following code can be used to dump the list into a newly 219 * allocated array of {@code String}: 220 * 221 * <pre>{@code 222 * String[] y = x.toArray(new String[0]); 223 * }</pre> 224 * 225 * Note that {@code toArray(new Object[0])} is identical in function to 226 * {@code toArray()}. 227 * 228 * @param a the array into which the elements of this list are to 229 * be stored, if it is big enough; otherwise, a new array of the 230 * same runtime type is allocated for this purpose. 231 * @return an array containing the elements of this list 232 * @throws ArrayStoreException if the runtime type of the specified array 233 * is not a supertype of the runtime type of every element in 234 * this list 235 * @throws NullPointerException if the specified array is null 236 */ 237 <T> T[] toArray(T[] a); 238 239 240 // Modification Operations 241 242 /** 243 * Appends the specified element to the end of this list (optional 244 * operation). 245 * 246 * <p>Lists that support this operation may place limitations on what 247 * elements may be added to this list. In particular, some 248 * lists will refuse to add null elements, and others will impose 249 * restrictions on the type of elements that may be added. List 250 * classes should clearly specify in their documentation any restrictions 251 * on what elements may be added. 252 * 253 * @param e element to be appended to this list 254 * @return {@code true} (as specified by {@link Collection#add}) 255 * @throws UnsupportedOperationException if the {@code add} operation 256 * is not supported by this list 257 * @throws ClassCastException if the class of the specified element 258 * prevents it from being added to this list 259 * @throws NullPointerException if the specified element is null and this 260 * list does not permit null elements 261 * @throws IllegalArgumentException if some property of this element 262 * prevents it from being added to this list 263 */ 264 boolean add(E e); 265 266 /** 267 * Removes the first occurrence of the specified element from this list, 268 * if it is present (optional operation). If this list does not contain 269 * the element, it is unchanged. More formally, removes the element with 270 * the lowest index {@code i} such that 271 * {@code Objects.equals(o, get(i))} 272 * (if such an element exists). Returns {@code true} if this list 273 * contained the specified element (or equivalently, if this list changed 274 * as a result of the call). 275 * 276 * @param o element to be removed from this list, if present 277 * @return {@code true} if this list contained the specified element 278 * @throws ClassCastException if the type of the specified element 279 * is incompatible with this list 280 * (<a href="Collection.html#optional-restrictions">optional</a>) 281 * @throws NullPointerException if the specified element is null and this 282 * list does not permit null elements 283 * (<a href="Collection.html#optional-restrictions">optional</a>) 284 * @throws UnsupportedOperationException if the {@code remove} operation 285 * is not supported by this list 286 */ 287 boolean remove(Object o); 288 289 290 // Bulk Modification Operations 291 292 /** 293 * Returns {@code true} if this list contains all of the elements of the 294 * specified collection. 295 * 296 * @param c collection to be checked for containment in this list 297 * @return {@code true} if this list contains all of the elements of the 298 * specified collection 299 * @throws ClassCastException if the types of one or more elements 300 * in the specified collection are incompatible with this 301 * list 302 * (<a href="Collection.html#optional-restrictions">optional</a>) 303 * @throws NullPointerException if the specified collection contains one 304 * or more null elements and this list does not permit null 305 * elements 306 * (<a href="Collection.html#optional-restrictions">optional</a>), 307 * or if the specified collection is null 308 * @see #contains(Object) 309 */ 310 boolean containsAll(Collection<?> c); 311 312 /** 313 * Appends all of the elements in the specified collection to the end of 314 * this list, in the order that they are returned by the specified 315 * collection's iterator (optional operation). The behavior of this 316 * operation is undefined if the specified collection is modified while 317 * the operation is in progress. (Note that this will occur if the 318 * specified collection is this list, and it's nonempty.) 319 * 320 * @param c collection containing elements to be added to this list 321 * @return {@code true} if this list changed as a result of the call 322 * @throws UnsupportedOperationException if the {@code addAll} operation 323 * is not supported by this list 324 * @throws ClassCastException if the class of an element of the specified 325 * collection prevents it from being added to this list 326 * @throws NullPointerException if the specified collection contains one 327 * or more null elements and this list does not permit null 328 * elements, or if the specified collection is null 329 * @throws IllegalArgumentException if some property of an element of the 330 * specified collection prevents it from being added to this list 331 * @see #add(Object) 332 */ 333 boolean addAll(Collection<? extends E> c); 334 335 /** 336 * Inserts all of the elements in the specified collection into this 337 * list at the specified position (optional operation). Shifts the 338 * element currently at that position (if any) and any subsequent 339 * elements to the right (increases their indices). The new elements 340 * will appear in this list in the order that they are returned by the 341 * specified collection's iterator. The behavior of this operation is 342 * undefined if the specified collection is modified while the 343 * operation is in progress. (Note that this will occur if the specified 344 * collection is this list, and it's nonempty.) 345 * 346 * @param index index at which to insert the first element from the 347 * specified collection 348 * @param c collection containing elements to be added to this list 349 * @return {@code true} if this list changed as a result of the call 350 * @throws UnsupportedOperationException if the {@code addAll} operation 351 * is not supported by this list 352 * @throws ClassCastException if the class of an element of the specified 353 * collection prevents it from being added to this list 354 * @throws NullPointerException if the specified collection contains one 355 * or more null elements and this list does not permit null 356 * elements, or if the specified collection is null 357 * @throws IllegalArgumentException if some property of an element of the 358 * specified collection prevents it from being added to this list 359 * @throws IndexOutOfBoundsException if the index is out of range 360 * ({@code index < 0 || index > size()}) 361 */ 362 boolean addAll(int index, Collection<? extends E> c); 363 364 /** 365 * Removes from this list all of its elements that are contained in the 366 * specified collection (optional operation). 367 * 368 * @param c collection containing elements to be removed from this list 369 * @return {@code true} if this list changed as a result of the call 370 * @throws UnsupportedOperationException if the {@code removeAll} operation 371 * is not supported by this list 372 * @throws ClassCastException if the class of an element of this list 373 * is incompatible with the specified collection 374 * (<a href="Collection.html#optional-restrictions">optional</a>) 375 * @throws NullPointerException if this list contains a null element and the 376 * specified collection does not permit null elements 377 * (<a href="Collection.html#optional-restrictions">optional</a>), 378 * or if the specified collection is null 379 * @see #remove(Object) 380 * @see #contains(Object) 381 */ 382 boolean removeAll(Collection<?> c); 383 384 /** 385 * Retains only the elements in this list that are contained in the 386 * specified collection (optional operation). In other words, removes 387 * from this list all of its elements that are not contained in the 388 * specified collection. 389 * 390 * @param c collection containing elements to be retained in this list 391 * @return {@code true} if this list changed as a result of the call 392 * @throws UnsupportedOperationException if the {@code retainAll} operation 393 * is not supported by this list 394 * @throws ClassCastException if the class of an element of this list 395 * is incompatible with the specified collection 396 * (<a href="Collection.html#optional-restrictions">optional</a>) 397 * @throws NullPointerException if this list contains a null element and the 398 * specified collection does not permit null elements 399 * (<a href="Collection.html#optional-restrictions">optional</a>), 400 * or if the specified collection is null 401 * @see #remove(Object) 402 * @see #contains(Object) 403 */ 404 boolean retainAll(Collection<?> c); 405 406 /** 407 * Replaces each element of this list with the result of applying the 408 * operator to that element. Errors or runtime exceptions thrown by 409 * the operator are relayed to the caller. 410 * 411 * @implSpec 412 * The default implementation is equivalent to, for this {@code list}: 413 * <pre>{@code 414 * final ListIterator<E> li = list.listIterator(); 415 * while (li.hasNext()) { 416 * li.set(operator.apply(li.next())); 417 * } 418 * }</pre> 419 * 420 * If the list's list-iterator does not support the {@code set} operation 421 * then an {@code UnsupportedOperationException} will be thrown when 422 * replacing the first element. 423 * 424 * @param operator the operator to apply to each element 425 * @throws UnsupportedOperationException if this list is unmodifiable. 426 * Implementations may throw this exception if an element 427 * cannot be replaced or if, in general, modification is not 428 * supported 429 * @throws NullPointerException if the specified operator is null or 430 * if the operator result is a null value and this list does 431 * not permit null elements 432 * (<a href="Collection.html#optional-restrictions">optional</a>) 433 * @since 1.8 434 */ 435 default void replaceAll(UnaryOperator<E> operator) { 436 Objects.requireNonNull(operator); 437 final ListIterator<E> li = this.listIterator(); 438 while (li.hasNext()) { 439 li.set(operator.apply(li.next())); 440 } 441 } 442 443 /** 444 * Sorts this list according to the order induced by the specified 445 * {@link Comparator}. 446 * 447 * <p>All elements in this list must be <i>mutually comparable</i> using the 448 * specified comparator (that is, {@code c.compare(e1, e2)} must not throw 449 * a {@code ClassCastException} for any elements {@code e1} and {@code e2} 450 * in the list). 451 * 452 * <p>If the specified comparator is {@code null} then all elements in this 453 * list must implement the {@link Comparable} interface and the elements' 454 * {@linkplain Comparable natural ordering} should be used. 455 * 456 * <p>This list must be modifiable, but need not be resizable. 457 * 458 * @implSpec 459 * The default implementation obtains an array containing all elements in 460 * this list, sorts the array, and iterates over this list resetting each 461 * element from the corresponding position in the array. (This avoids the 462 * n<sup>2</sup> log(n) performance that would result from attempting 463 * to sort a linked list in place.) 464 * 465 * @implNote 466 * This implementation is a stable, adaptive, iterative mergesort that 467 * requires far fewer than n lg(n) comparisons when the input array is 468 * partially sorted, while offering the performance of a traditional 469 * mergesort when the input array is randomly ordered. If the input array 470 * is nearly sorted, the implementation requires approximately n 471 * comparisons. Temporary storage requirements vary from a small constant 472 * for nearly sorted input arrays to n/2 object references for randomly 473 * ordered input arrays. 474 * 475 * <p>The implementation takes equal advantage of ascending and 476 * descending order in its input array, and can take advantage of 477 * ascending and descending order in different parts of the same 478 * input array. It is well-suited to merging two or more sorted arrays: 479 * simply concatenate the arrays and sort the resulting array. 480 * 481 * <p>The implementation was adapted from Tim Peters's list sort for Python 482 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 483 * TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic 484 * Sorting and Information Theoretic Complexity", in Proceedings of the 485 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 486 * January 1993. 487 * 488 * @param c the {@code Comparator} used to compare list elements. 489 * A {@code null} value indicates that the elements' 490 * {@linkplain Comparable natural ordering} should be used 491 * @throws ClassCastException if the list contains elements that are not 492 * <i>mutually comparable</i> using the specified comparator 493 * @throws UnsupportedOperationException if the list's list-iterator does 494 * not support the {@code set} operation 495 * @throws IllegalArgumentException 496 * (<a href="Collection.html#optional-restrictions">optional</a>) 497 * if the comparator is found to violate the {@link Comparator} 498 * contract 499 * @since 1.8 500 */ 501 @SuppressWarnings({"unchecked", "rawtypes"}) 502 default void sort(Comparator<? super E> c) { 503 Object[] a = this.toArray(); 504 Arrays.sort(a, (Comparator) c); 505 ListIterator<E> i = this.listIterator(); 506 for (Object e : a) { 507 i.next(); 508 i.set((E) e); 509 } 510 } 511 512 /** 513 * Removes all of the elements from this list (optional operation). 514 * The list will be empty after this call returns. 515 * 516 * @throws UnsupportedOperationException if the {@code clear} operation 517 * is not supported by this list 518 */ 519 void clear(); 520 521 522 // Comparison and hashing 523 524 /** 525 * Compares the specified object with this list for equality. Returns 526 * {@code true} if and only if the specified object is also a list, both 527 * lists have the same size, and all corresponding pairs of elements in 528 * the two lists are <i>equal</i>. (Two elements {@code e1} and 529 * {@code e2} are <i>equal</i> if {@code Objects.equals(e1, e2)}.) 530 * In other words, two lists are defined to be 531 * equal if they contain the same elements in the same order. This 532 * definition ensures that the equals method works properly across 533 * different implementations of the {@code List} interface. 534 * 535 * @param o the object to be compared for equality with this list 536 * @return {@code true} if the specified object is equal to this list 537 */ 538 boolean equals(Object o); 539 540 /** 541 * Returns the hash code value for this list. The hash code of a list 542 * is defined to be the result of the following calculation: 543 * <pre>{@code 544 * int hashCode = 1; 545 * for (E e : list) 546 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode()); 547 * }</pre> 548 * This ensures that {@code list1.equals(list2)} implies that 549 * {@code list1.hashCode()==list2.hashCode()} for any two lists, 550 * {@code list1} and {@code list2}, as required by the general 551 * contract of {@link Object#hashCode}. 552 * 553 * @return the hash code value for this list 554 * @see Object#equals(Object) 555 * @see #equals(Object) 556 */ 557 int hashCode(); 558 559 560 // Positional Access Operations 561 562 /** 563 * Returns the element at the specified position in this list. 564 * 565 * @param index index of the element to return 566 * @return the element at the specified position in this list 567 * @throws IndexOutOfBoundsException if the index is out of range 568 * ({@code index < 0 || index >= size()}) 569 */ 570 E get(int index); 571 572 /** 573 * Replaces the element at the specified position in this list with the 574 * specified element (optional operation). 575 * 576 * @param index index of the element to replace 577 * @param element element to be stored at the specified position 578 * @return the element previously at the specified position 579 * @throws UnsupportedOperationException if the {@code set} operation 580 * is not supported by this list 581 * @throws ClassCastException if the class of the specified element 582 * prevents it from being added to this list 583 * @throws NullPointerException if the specified element is null and 584 * this list does not permit null elements 585 * @throws IllegalArgumentException if some property of the specified 586 * element prevents it from being added to this list 587 * @throws IndexOutOfBoundsException if the index is out of range 588 * ({@code index < 0 || index >= size()}) 589 */ 590 E set(int index, E element); 591 592 /** 593 * Inserts the specified element at the specified position in this list 594 * (optional operation). Shifts the element currently at that position 595 * (if any) and any subsequent elements to the right (adds one to their 596 * indices). 597 * 598 * @param index index at which the specified element is to be inserted 599 * @param element element to be inserted 600 * @throws UnsupportedOperationException if the {@code add} operation 601 * is not supported by this list 602 * @throws ClassCastException if the class of the specified element 603 * prevents it from being added to this list 604 * @throws NullPointerException if the specified element is null and 605 * this list does not permit null elements 606 * @throws IllegalArgumentException if some property of the specified 607 * element prevents it from being added to this list 608 * @throws IndexOutOfBoundsException if the index is out of range 609 * ({@code index < 0 || index > size()}) 610 */ 611 void add(int index, E element); 612 613 /** 614 * Removes the element at the specified position in this list (optional 615 * operation). Shifts any subsequent elements to the left (subtracts one 616 * from their indices). Returns the element that was removed from the 617 * list. 618 * 619 * @param index the index of the element to be removed 620 * @return the element previously at the specified position 621 * @throws UnsupportedOperationException if the {@code remove} operation 622 * is not supported by this list 623 * @throws IndexOutOfBoundsException if the index is out of range 624 * ({@code index < 0 || index >= size()}) 625 */ 626 E remove(int index); 627 628 629 // Search Operations 630 631 /** 632 * Returns the index of the first occurrence of the specified element 633 * in this list, or -1 if this list does not contain the element. 634 * More formally, returns the lowest index {@code i} such that 635 * {@code Objects.equals(o, get(i))}, 636 * or -1 if there is no such index. 637 * 638 * @param o element to search for 639 * @return the index of the first occurrence of the specified element in 640 * this list, or -1 if this list does not contain the element 641 * @throws ClassCastException if the type of the specified element 642 * is incompatible with this list 643 * (<a href="Collection.html#optional-restrictions">optional</a>) 644 * @throws NullPointerException if the specified element is null and this 645 * list does not permit null elements 646 * (<a href="Collection.html#optional-restrictions">optional</a>) 647 */ 648 int indexOf(Object o); 649 650 /** 651 * Returns the index of the last occurrence of the specified element 652 * in this list, or -1 if this list does not contain the element. 653 * More formally, returns the highest index {@code i} such that 654 * {@code Objects.equals(o, get(i))}, 655 * or -1 if there is no such index. 656 * 657 * @param o element to search for 658 * @return the index of the last occurrence of the specified element in 659 * this list, or -1 if this list does not contain the element 660 * @throws ClassCastException if the type of the specified element 661 * is incompatible with this list 662 * (<a href="Collection.html#optional-restrictions">optional</a>) 663 * @throws NullPointerException if the specified element is null and this 664 * list does not permit null elements 665 * (<a href="Collection.html#optional-restrictions">optional</a>) 666 */ 667 int lastIndexOf(Object o); 668 669 670 // List Iterators 671 672 /** 673 * Returns a list iterator over the elements in this list (in proper 674 * sequence). 675 * 676 * @return a list iterator over the elements in this list (in proper 677 * sequence) 678 */ 679 ListIterator<E> listIterator(); 680 681 /** 682 * Returns a list iterator over the elements in this list (in proper 683 * sequence), starting at the specified position in the list. 684 * The specified index indicates the first element that would be 685 * returned by an initial call to {@link ListIterator#next next}. 686 * An initial call to {@link ListIterator#previous previous} would 687 * return the element with the specified index minus one. 688 * 689 * @param index index of the first element to be returned from the 690 * list iterator (by a call to {@link ListIterator#next next}) 691 * @return a list iterator over the elements in this list (in proper 692 * sequence), starting at the specified position in the list 693 * @throws IndexOutOfBoundsException if the index is out of range 694 * ({@code index < 0 || index > size()}) 695 */ 696 ListIterator<E> listIterator(int index); 697 698 // View 699 700 /** 701 * Returns a view of the portion of this list between the specified 702 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If 703 * {@code fromIndex} and {@code toIndex} are equal, the returned list is 704 * empty.) The returned list is backed by this list, so non-structural 705 * changes in the returned list are reflected in this list, and vice-versa. 706 * The returned list supports all of the optional list operations supported 707 * by this list.<p> 708 * 709 * This method eliminates the need for explicit range operations (of 710 * the sort that commonly exist for arrays). Any operation that expects 711 * a list can be used as a range operation by passing a subList view 712 * instead of a whole list. For example, the following idiom 713 * removes a range of elements from a list: 714 * <pre>{@code 715 * list.subList(from, to).clear(); 716 * }</pre> 717 * Similar idioms may be constructed for {@code indexOf} and 718 * {@code lastIndexOf}, and all of the algorithms in the 719 * {@code Collections} class can be applied to a subList.<p> 720 * 721 * The semantics of the list returned by this method become undefined if 722 * the backing list (i.e., this list) is <i>structurally modified</i> in 723 * any way other than via the returned list. (Structural modifications are 724 * those that change the size of this list, or otherwise perturb it in such 725 * a fashion that iterations in progress may yield incorrect results.) 726 * 727 * @param fromIndex low endpoint (inclusive) of the subList 728 * @param toIndex high endpoint (exclusive) of the subList 729 * @return a view of the specified range within this list 730 * @throws IndexOutOfBoundsException for an illegal endpoint index value 731 * ({@code fromIndex < 0 || toIndex > size || 732 * fromIndex > toIndex}) 733 */ 734 List<E> subList(int fromIndex, int toIndex); 735 736 /** 737 * Creates a {@link Spliterator} over the elements in this list. 738 * 739 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and 740 * {@link Spliterator#ORDERED}. Implementations should document the 741 * reporting of additional characteristic values. 742 * 743 * @implSpec 744 * The default implementation creates a 745 * <em><a href="Spliterator.html#binding">late-binding</a></em> 746 * spliterator as follows: 747 * <ul> 748 * <li>If the list is an instance of {@link RandomAccess} then the default 749 * implementation creates a spliterator that traverses elements by 750 * invoking the method {@link List#get}. If such invocation results or 751 * would result in an {@code IndexOutOfBoundsException} then the 752 * spliterator will <em>fail-fast</em> and throw a 753 * {@code ConcurrentModificationException}. 754 * If the list is also an instance of {@link AbstractList} then the 755 * spliterator will use the list's {@link AbstractList#modCount modCount} 756 * field to provide additional <em>fail-fast</em> behavior. 757 * <li>Otherwise, the default implementation creates a spliterator from the 758 * list's {@code Iterator}. The spliterator inherits the 759 * <em>fail-fast</em> of the list's iterator. 760 * </ul> 761 * 762 * @implNote 763 * The created {@code Spliterator} additionally reports 764 * {@link Spliterator#SUBSIZED}. 765 * 766 * @return a {@code Spliterator} over the elements in this list 767 * @since 1.8 768 */ 769 @Override 770 default Spliterator<E> spliterator() { 771 if (this instanceof RandomAccess) { 772 return new AbstractList.RandomAccessSpliterator<>(this); 773 } else { 774 return Spliterators.spliterator(this, Spliterator.ORDERED); 775 } 776 } 777 778 /** 779 * Returns an immutable list containing zero elements. 780 * 781 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 782 * 783 * @param <E> the {@code List}'s element type 784 * @return an empty {@code List} 785 * 786 * @since 9 787 */ 788 static <E> List<E> of() { 789 return ImmutableCollections.List0.instance(); 790 } 791 792 /** 793 * Returns an immutable list containing one element. 794 * 795 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 796 * 797 * @param <E> the {@code List}'s element type 798 * @param e1 the single element 799 * @return a {@code List} containing the specified element 800 * @throws NullPointerException if the element is {@code null} 801 * 802 * @since 9 803 */ 804 static <E> List<E> of(E e1) { 805 return new ImmutableCollections.List1<>(e1); 806 } 807 808 /** 809 * Returns an immutable list containing two elements. 810 * 811 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 812 * 813 * @param <E> the {@code List}'s element type 814 * @param e1 the first element 815 * @param e2 the second element 816 * @return a {@code List} containing the specified elements 817 * @throws NullPointerException if an element is {@code null} 818 * 819 * @since 9 820 */ 821 static <E> List<E> of(E e1, E e2) { 822 return new ImmutableCollections.List2<>(e1, e2); 823 } 824 825 /** 826 * Returns an immutable list containing three elements. 827 * 828 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 829 * 830 * @param <E> the {@code List}'s element type 831 * @param e1 the first element 832 * @param e2 the second element 833 * @param e3 the third element 834 * @return a {@code List} containing the specified elements 835 * @throws NullPointerException if an element is {@code null} 836 * 837 * @since 9 838 */ 839 static <E> List<E> of(E e1, E e2, E e3) { 840 return new ImmutableCollections.ListN<>(e1, e2, e3); 841 } 842 843 /** 844 * Returns an immutable list containing four elements. 845 * 846 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 847 * 848 * @param <E> the {@code List}'s element type 849 * @param e1 the first element 850 * @param e2 the second element 851 * @param e3 the third element 852 * @param e4 the fourth element 853 * @return a {@code List} containing the specified elements 854 * @throws NullPointerException if an element is {@code null} 855 * 856 * @since 9 857 */ 858 static <E> List<E> of(E e1, E e2, E e3, E e4) { 859 return new ImmutableCollections.ListN<>(e1, e2, e3, e4); 860 } 861 862 /** 863 * Returns an immutable list containing five elements. 864 * 865 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 866 * 867 * @param <E> the {@code List}'s element type 868 * @param e1 the first element 869 * @param e2 the second element 870 * @param e3 the third element 871 * @param e4 the fourth element 872 * @param e5 the fifth element 873 * @return a {@code List} containing the specified elements 874 * @throws NullPointerException if an element is {@code null} 875 * 876 * @since 9 877 */ 878 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5) { 879 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5); 880 } 881 882 /** 883 * Returns an immutable list containing six elements. 884 * 885 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 886 * 887 * @param <E> the {@code List}'s element type 888 * @param e1 the first element 889 * @param e2 the second element 890 * @param e3 the third element 891 * @param e4 the fourth element 892 * @param e5 the fifth element 893 * @param e6 the sixth element 894 * @return a {@code List} containing the specified elements 895 * @throws NullPointerException if an element is {@code null} 896 * 897 * @since 9 898 */ 899 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6) { 900 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 901 e6); 902 } 903 904 /** 905 * Returns an immutable list containing seven elements. 906 * 907 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 908 * 909 * @param <E> the {@code List}'s element type 910 * @param e1 the first element 911 * @param e2 the second element 912 * @param e3 the third element 913 * @param e4 the fourth element 914 * @param e5 the fifth element 915 * @param e6 the sixth element 916 * @param e7 the seventh element 917 * @return a {@code List} containing the specified elements 918 * @throws NullPointerException if an element is {@code null} 919 * 920 * @since 9 921 */ 922 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) { 923 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 924 e6, e7); 925 } 926 927 /** 928 * Returns an immutable list containing eight elements. 929 * 930 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 931 * 932 * @param <E> the {@code List}'s element type 933 * @param e1 the first element 934 * @param e2 the second element 935 * @param e3 the third element 936 * @param e4 the fourth element 937 * @param e5 the fifth element 938 * @param e6 the sixth element 939 * @param e7 the seventh element 940 * @param e8 the eighth element 941 * @return a {@code List} containing the specified elements 942 * @throws NullPointerException if an element is {@code null} 943 * 944 * @since 9 945 */ 946 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) { 947 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 948 e6, e7, e8); 949 } 950 951 /** 952 * Returns an immutable list containing nine elements. 953 * 954 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 955 * 956 * @param <E> the {@code List}'s element type 957 * @param e1 the first element 958 * @param e2 the second element 959 * @param e3 the third element 960 * @param e4 the fourth element 961 * @param e5 the fifth element 962 * @param e6 the sixth element 963 * @param e7 the seventh element 964 * @param e8 the eighth element 965 * @param e9 the ninth element 966 * @return a {@code List} containing the specified elements 967 * @throws NullPointerException if an element is {@code null} 968 * 969 * @since 9 970 */ 971 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) { 972 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 973 e6, e7, e8, e9); 974 } 975 976 /** 977 * Returns an immutable list containing ten elements. 978 * 979 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 980 * 981 * @param <E> the {@code List}'s element type 982 * @param e1 the first element 983 * @param e2 the second element 984 * @param e3 the third element 985 * @param e4 the fourth element 986 * @param e5 the fifth element 987 * @param e6 the sixth element 988 * @param e7 the seventh element 989 * @param e8 the eighth element 990 * @param e9 the ninth element 991 * @param e10 the tenth element 992 * @return a {@code List} containing the specified elements 993 * @throws NullPointerException if an element is {@code null} 994 * 995 * @since 9 996 */ 997 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) { 998 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 999 e6, e7, e8, e9, e10); 1000 } 1001 1002 /** 1003 * Returns an immutable list containing an arbitrary number of elements. 1004 * See <a href="#immutable">Immutable List Static Factory Methods</a> for details. 1005 * 1006 * @apiNote 1007 * This method also accepts a single array as an argument. The element type of 1008 * the resulting list will be the component type of the array, and the size of 1009 * the list will be equal to the length of the array. To create a list with 1010 * a single element that is an array, do the following: 1011 * 1012 * <pre>{@code 1013 * String[] array = ... ; 1014 * List<String[]> list = List.<String[]>of(array); 1015 * }</pre> 1016 * 1017 * This will cause the {@link List#of(Object) List.of(E)} method 1018 * to be invoked instead. 1019 * 1020 * @param <E> the {@code List}'s element type 1021 * @param elements the elements to be contained in the list 1022 * @return a {@code List} containing the specified elements 1023 * @throws NullPointerException if an element is {@code null} or if the array is {@code null} 1024 * 1025 * @since 9 1026 */ 1027 @SafeVarargs 1028 @SuppressWarnings("varargs") 1029 static <E> List<E> of(E... elements) { 1030 switch (elements.length) { // implicit null check of elements 1031 case 0: 1032 return ImmutableCollections.List0.instance(); 1033 case 1: 1034 return new ImmutableCollections.List1<>(elements[0]); 1035 case 2: 1036 return new ImmutableCollections.List2<>(elements[0], elements[1]); 1037 default: 1038 return new ImmutableCollections.ListN<>(elements); 1039 } 1040 } 1041} 1042