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}. 447 * 448 * <p>All elements in this list must be <i>mutually comparable</i> using the 449 * specified comparator (that is, {@code c.compare(e1, e2)} must not throw 450 * a {@code ClassCastException} for any elements {@code e1} and {@code e2} 451 * in the list). 452 * 453 * <p>If the specified comparator is {@code null} then all elements in this 454 * list must implement the {@link Comparable} interface and the elements' 455 * {@linkplain Comparable natural ordering} should be used. 456 * 457 * <p>This list must be modifiable, but need not be resizable. 458 * 459 * @implSpec 460 * The default implementation obtains an array containing all elements in 461 * this list, sorts the array, and iterates over this list resetting each 462 * element from the corresponding position in the array. (This avoids the 463 * n<sup>2</sup> log(n) performance that would result from attempting 464 * to sort a linked list in place.) 465 * 466 * @implNote 467 * This implementation is a stable, adaptive, iterative mergesort that 468 * requires far fewer than n lg(n) comparisons when the input array is 469 * partially sorted, while offering the performance of a traditional 470 * mergesort when the input array is randomly ordered. If the input array 471 * is nearly sorted, the implementation requires approximately n 472 * comparisons. Temporary storage requirements vary from a small constant 473 * for nearly sorted input arrays to n/2 object references for randomly 474 * ordered input arrays. 475 * 476 * <p>The implementation takes equal advantage of ascending and 477 * descending order in its input array, and can take advantage of 478 * ascending and descending order in different parts of the same 479 * input array. It is well-suited to merging two or more sorted arrays: 480 * simply concatenate the arrays and sort the resulting array. 481 * 482 * <p>The implementation was adapted from Tim Peters's list sort for Python 483 * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt"> 484 * TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic 485 * Sorting and Information Theoretic Complexity", in Proceedings of the 486 * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474, 487 * January 1993. 488 * 489 * @param c the {@code Comparator} used to compare list elements. 490 * A {@code null} value indicates that the elements' 491 * {@linkplain Comparable natural ordering} should be used 492 * @throws ClassCastException if the list contains elements that are not 493 * <i>mutually comparable</i> using the specified comparator 494 * @throws UnsupportedOperationException if the list's list-iterator does 495 * not support the {@code set} operation 496 * @throws IllegalArgumentException 497 * (<a href="Collection.html#optional-restrictions">optional</a>) 498 * if the comparator is found to violate the {@link Comparator} 499 * contract 500 * @since 1.8 501 */ 502 @SuppressWarnings({"unchecked", "rawtypes"}) 503 default void sort(Comparator<? super E> c) { 504 Object[] a = this.toArray(); 505 Arrays.sort(a, (Comparator) c); 506 ListIterator<E> i = this.listIterator(); 507 for (Object e : a) { 508 i.next(); 509 i.set((E) e); 510 } 511 } 512 513 /** 514 * Removes all of the elements from this list (optional operation). 515 * The list will be empty after this call returns. 516 * 517 * @throws UnsupportedOperationException if the {@code clear} operation 518 * is not supported by this list 519 */ 520 void clear(); 521 522 523 // Comparison and hashing 524 525 /** 526 * Compares the specified object with this list for equality. Returns 527 * {@code true} if and only if the specified object is also a list, both 528 * lists have the same size, and all corresponding pairs of elements in 529 * the two lists are <i>equal</i>. (Two elements {@code e1} and 530 * {@code e2} are <i>equal</i> if {@code Objects.equals(e1, e2)}.) 531 * In other words, two lists are defined to be 532 * equal if they contain the same elements in the same order. This 533 * definition ensures that the equals method works properly across 534 * different implementations of the {@code List} interface. 535 * 536 * @param o the object to be compared for equality with this list 537 * @return {@code true} if the specified object is equal to this list 538 */ 539 boolean equals(Object o); 540 541 /** 542 * Returns the hash code value for this list. The hash code of a list 543 * is defined to be the result of the following calculation: 544 * <pre>{@code 545 * int hashCode = 1; 546 * for (E e : list) 547 * hashCode = 31*hashCode + (e==null ? 0 : e.hashCode()); 548 * }</pre> 549 * This ensures that {@code list1.equals(list2)} implies that 550 * {@code list1.hashCode()==list2.hashCode()} for any two lists, 551 * {@code list1} and {@code list2}, as required by the general 552 * contract of {@link Object#hashCode}. 553 * 554 * @return the hash code value for this list 555 * @see Object#equals(Object) 556 * @see #equals(Object) 557 */ 558 int hashCode(); 559 560 561 // Positional Access Operations 562 563 /** 564 * Returns the element at the specified position in this list. 565 * 566 * @param index index of the element to return 567 * @return the element at the specified position in this list 568 * @throws IndexOutOfBoundsException if the index is out of range 569 * ({@code index < 0 || index >= size()}) 570 */ 571 E get(int index); 572 573 /** 574 * Replaces the element at the specified position in this list with the 575 * specified element (optional operation). 576 * 577 * @param index index of the element to replace 578 * @param element element to be stored at the specified position 579 * @return the element previously at the specified position 580 * @throws UnsupportedOperationException if the {@code set} operation 581 * is not supported by this list 582 * @throws ClassCastException if the class of the specified element 583 * prevents it from being added to this list 584 * @throws NullPointerException if the specified element is null and 585 * this list does not permit null elements 586 * @throws IllegalArgumentException if some property of the specified 587 * element prevents it from being added to this list 588 * @throws IndexOutOfBoundsException if the index is out of range 589 * ({@code index < 0 || index >= size()}) 590 */ 591 E set(int index, E element); 592 593 /** 594 * Inserts the specified element at the specified position in this list 595 * (optional operation). Shifts the element currently at that position 596 * (if any) and any subsequent elements to the right (adds one to their 597 * indices). 598 * 599 * @param index index at which the specified element is to be inserted 600 * @param element element to be inserted 601 * @throws UnsupportedOperationException if the {@code add} operation 602 * is not supported by this list 603 * @throws ClassCastException if the class of the specified element 604 * prevents it from being added to this list 605 * @throws NullPointerException if the specified element is null and 606 * this list does not permit null elements 607 * @throws IllegalArgumentException if some property of the specified 608 * element prevents it from being added to this list 609 * @throws IndexOutOfBoundsException if the index is out of range 610 * ({@code index < 0 || index > size()}) 611 */ 612 void add(int index, E element); 613 614 /** 615 * Removes the element at the specified position in this list (optional 616 * operation). Shifts any subsequent elements to the left (subtracts one 617 * from their indices). Returns the element that was removed from the 618 * list. 619 * 620 * @param index the index of the element to be removed 621 * @return the element previously at the specified position 622 * @throws UnsupportedOperationException if the {@code remove} operation 623 * is not supported by this list 624 * @throws IndexOutOfBoundsException if the index is out of range 625 * ({@code index < 0 || index >= size()}) 626 */ 627 E remove(int index); 628 629 630 // Search Operations 631 632 /** 633 * Returns the index of the first occurrence of the specified element 634 * in this list, or -1 if this list does not contain the element. 635 * More formally, returns the lowest index {@code i} such that 636 * {@code Objects.equals(o, get(i))}, 637 * or -1 if there is no such index. 638 * 639 * @param o element to search for 640 * @return the index of the first occurrence of the specified element in 641 * this list, or -1 if this list does not contain the element 642 * @throws ClassCastException if the type of the specified element 643 * is incompatible with this list 644 * (<a href="Collection.html#optional-restrictions">optional</a>) 645 * @throws NullPointerException if the specified element is null and this 646 * list does not permit null elements 647 * (<a href="Collection.html#optional-restrictions">optional</a>) 648 */ 649 int indexOf(Object o); 650 651 /** 652 * Returns the index of the last occurrence of the specified element 653 * in this list, or -1 if this list does not contain the element. 654 * More formally, returns the highest index {@code i} such that 655 * {@code Objects.equals(o, get(i))}, 656 * or -1 if there is no such index. 657 * 658 * @param o element to search for 659 * @return the index of the last occurrence of the specified element in 660 * this list, or -1 if this list does not contain the element 661 * @throws ClassCastException if the type of the specified element 662 * is incompatible with this list 663 * (<a href="Collection.html#optional-restrictions">optional</a>) 664 * @throws NullPointerException if the specified element is null and this 665 * list does not permit null elements 666 * (<a href="Collection.html#optional-restrictions">optional</a>) 667 */ 668 int lastIndexOf(Object o); 669 670 671 // List Iterators 672 673 /** 674 * Returns a list iterator over the elements in this list (in proper 675 * sequence). 676 * 677 * @return a list iterator over the elements in this list (in proper 678 * sequence) 679 */ 680 ListIterator<E> listIterator(); 681 682 /** 683 * Returns a list iterator over the elements in this list (in proper 684 * sequence), starting at the specified position in the list. 685 * The specified index indicates the first element that would be 686 * returned by an initial call to {@link ListIterator#next next}. 687 * An initial call to {@link ListIterator#previous previous} would 688 * return the element with the specified index minus one. 689 * 690 * @param index index of the first element to be returned from the 691 * list iterator (by a call to {@link ListIterator#next next}) 692 * @return a list iterator over the elements in this list (in proper 693 * sequence), starting at the specified position in the list 694 * @throws IndexOutOfBoundsException if the index is out of range 695 * ({@code index < 0 || index > size()}) 696 */ 697 ListIterator<E> listIterator(int index); 698 699 // View 700 701 /** 702 * Returns a view of the portion of this list between the specified 703 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If 704 * {@code fromIndex} and {@code toIndex} are equal, the returned list is 705 * empty.) The returned list is backed by this list, so non-structural 706 * changes in the returned list are reflected in this list, and vice-versa. 707 * The returned list supports all of the optional list operations supported 708 * by this list.<p> 709 * 710 * This method eliminates the need for explicit range operations (of 711 * the sort that commonly exist for arrays). Any operation that expects 712 * a list can be used as a range operation by passing a subList view 713 * instead of a whole list. For example, the following idiom 714 * removes a range of elements from a list: 715 * <pre>{@code 716 * list.subList(from, to).clear(); 717 * }</pre> 718 * Similar idioms may be constructed for {@code indexOf} and 719 * {@code lastIndexOf}, and all of the algorithms in the 720 * {@code Collections} class can be applied to a subList.<p> 721 * 722 * The semantics of the list returned by this method become undefined if 723 * the backing list (i.e., this list) is <i>structurally modified</i> in 724 * any way other than via the returned list. (Structural modifications are 725 * those that change the size of this list, or otherwise perturb it in such 726 * a fashion that iterations in progress may yield incorrect results.) 727 * 728 * @param fromIndex low endpoint (inclusive) of the subList 729 * @param toIndex high endpoint (exclusive) of the subList 730 * @return a view of the specified range within this list 731 * @throws IndexOutOfBoundsException for an illegal endpoint index value 732 * ({@code fromIndex < 0 || toIndex > size || 733 * fromIndex > toIndex}) 734 */ 735 List<E> subList(int fromIndex, int toIndex); 736 737 /** 738 * Creates a {@link Spliterator} over the elements in this list. 739 * 740 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and 741 * {@link Spliterator#ORDERED}. Implementations should document the 742 * reporting of additional characteristic values. 743 * 744 * @implSpec 745 * The default implementation creates a 746 * <em><a href="Spliterator.html#binding">late-binding</a></em> 747 * spliterator as follows: 748 * <ul> 749 * <li>If the list is an instance of {@link RandomAccess} then the default 750 * implementation creates a spliterator that traverses elements by 751 * invoking the method {@link List#get}. If such invocation results or 752 * would result in an {@code IndexOutOfBoundsException} then the 753 * spliterator will <em>fail-fast</em> and throw a 754 * {@code ConcurrentModificationException}. 755 * If the list is also an instance of {@link AbstractList} then the 756 * spliterator will use the list's {@link AbstractList#modCount modCount} 757 * field to provide additional <em>fail-fast</em> behavior. 758 * <li>Otherwise, the default implementation creates a spliterator from the 759 * list's {@code Iterator}. The spliterator inherits the 760 * <em>fail-fast</em> of the list's iterator. 761 * </ul> 762 * 763 * @implNote 764 * The created {@code Spliterator} additionally reports 765 * {@link Spliterator#SUBSIZED}. 766 * 767 * @return a {@code Spliterator} over the elements in this list 768 * @since 1.8 769 */ 770 @Override 771 default Spliterator<E> spliterator() { 772 if (this instanceof RandomAccess) { 773 return new AbstractList.RandomAccessSpliterator<>(this); 774 } else { 775 return Spliterators.spliterator(this, Spliterator.ORDERED); 776 } 777 } 778 779 /** 780 * Returns an unmodifiable list containing zero elements. 781 * 782 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 783 * 784 * @param <E> the {@code List}'s element type 785 * @return an empty {@code List} 786 * 787 * @since 9 788 */ 789 static <E> List<E> of() { 790 return ImmutableCollections.List0.instance(); 791 } 792 793 /** 794 * Returns an unmodifiable list containing one element. 795 * 796 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 797 * 798 * @param <E> the {@code List}'s element type 799 * @param e1 the single element 800 * @return a {@code List} containing the specified element 801 * @throws NullPointerException if the element is {@code null} 802 * 803 * @since 9 804 */ 805 static <E> List<E> of(E e1) { 806 return new ImmutableCollections.List1<>(e1); 807 } 808 809 /** 810 * Returns an unmodifiable list containing two elements. 811 * 812 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 813 * 814 * @param <E> the {@code List}'s element type 815 * @param e1 the first element 816 * @param e2 the second element 817 * @return a {@code List} containing the specified elements 818 * @throws NullPointerException if an element is {@code null} 819 * 820 * @since 9 821 */ 822 static <E> List<E> of(E e1, E e2) { 823 return new ImmutableCollections.List2<>(e1, e2); 824 } 825 826 /** 827 * Returns an unmodifiable list containing three elements. 828 * 829 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 830 * 831 * @param <E> the {@code List}'s element type 832 * @param e1 the first element 833 * @param e2 the second element 834 * @param e3 the third element 835 * @return a {@code List} containing the specified elements 836 * @throws NullPointerException if an element is {@code null} 837 * 838 * @since 9 839 */ 840 static <E> List<E> of(E e1, E e2, E e3) { 841 return new ImmutableCollections.ListN<>(e1, e2, e3); 842 } 843 844 /** 845 * Returns an unmodifiable list containing four elements. 846 * 847 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 848 * 849 * @param <E> the {@code List}'s element type 850 * @param e1 the first element 851 * @param e2 the second element 852 * @param e3 the third element 853 * @param e4 the fourth element 854 * @return a {@code List} containing the specified elements 855 * @throws NullPointerException if an element is {@code null} 856 * 857 * @since 9 858 */ 859 static <E> List<E> of(E e1, E e2, E e3, E e4) { 860 return new ImmutableCollections.ListN<>(e1, e2, e3, e4); 861 } 862 863 /** 864 * Returns an unmodifiable list containing five elements. 865 * 866 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 867 * 868 * @param <E> the {@code List}'s element type 869 * @param e1 the first element 870 * @param e2 the second element 871 * @param e3 the third element 872 * @param e4 the fourth element 873 * @param e5 the fifth element 874 * @return a {@code List} containing the specified elements 875 * @throws NullPointerException if an element is {@code null} 876 * 877 * @since 9 878 */ 879 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5) { 880 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5); 881 } 882 883 /** 884 * Returns an unmodifiable list containing six elements. 885 * 886 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 887 * 888 * @param <E> the {@code List}'s element type 889 * @param e1 the first element 890 * @param e2 the second element 891 * @param e3 the third element 892 * @param e4 the fourth element 893 * @param e5 the fifth element 894 * @param e6 the sixth element 895 * @return a {@code List} containing the specified elements 896 * @throws NullPointerException if an element is {@code null} 897 * 898 * @since 9 899 */ 900 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6) { 901 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 902 e6); 903 } 904 905 /** 906 * Returns an unmodifiable list containing seven elements. 907 * 908 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 909 * 910 * @param <E> the {@code List}'s element type 911 * @param e1 the first element 912 * @param e2 the second element 913 * @param e3 the third element 914 * @param e4 the fourth element 915 * @param e5 the fifth element 916 * @param e6 the sixth element 917 * @param e7 the seventh element 918 * @return a {@code List} containing the specified elements 919 * @throws NullPointerException if an element is {@code null} 920 * 921 * @since 9 922 */ 923 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) { 924 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 925 e6, e7); 926 } 927 928 /** 929 * Returns an unmodifiable list containing eight elements. 930 * 931 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 932 * 933 * @param <E> the {@code List}'s element type 934 * @param e1 the first element 935 * @param e2 the second element 936 * @param e3 the third element 937 * @param e4 the fourth element 938 * @param e5 the fifth element 939 * @param e6 the sixth element 940 * @param e7 the seventh element 941 * @param e8 the eighth element 942 * @return a {@code List} containing the specified elements 943 * @throws NullPointerException if an element is {@code null} 944 * 945 * @since 9 946 */ 947 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) { 948 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 949 e6, e7, e8); 950 } 951 952 /** 953 * Returns an unmodifiable list containing nine elements. 954 * 955 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 956 * 957 * @param <E> the {@code List}'s element type 958 * @param e1 the first element 959 * @param e2 the second element 960 * @param e3 the third element 961 * @param e4 the fourth element 962 * @param e5 the fifth element 963 * @param e6 the sixth element 964 * @param e7 the seventh element 965 * @param e8 the eighth element 966 * @param e9 the ninth element 967 * @return a {@code List} containing the specified elements 968 * @throws NullPointerException if an element is {@code null} 969 * 970 * @since 9 971 */ 972 static <E> List<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) { 973 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 974 e6, e7, e8, e9); 975 } 976 977 /** 978 * Returns an unmodifiable list containing ten elements. 979 * 980 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 981 * 982 * @param <E> the {@code List}'s element type 983 * @param e1 the first element 984 * @param e2 the second element 985 * @param e3 the third element 986 * @param e4 the fourth element 987 * @param e5 the fifth element 988 * @param e6 the sixth element 989 * @param e7 the seventh element 990 * @param e8 the eighth element 991 * @param e9 the ninth element 992 * @param e10 the tenth element 993 * @return a {@code List} containing the specified elements 994 * @throws NullPointerException if an element is {@code null} 995 * 996 * @since 9 997 */ 998 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) { 999 return new ImmutableCollections.ListN<>(e1, e2, e3, e4, e5, 1000 e6, e7, e8, e9, e10); 1001 } 1002 1003 /** 1004 * Returns an unmodifiable list containing an arbitrary number of elements. 1005 * See <a href="#unmodifiable">Unmodifiable Lists</a> for details. 1006 * 1007 * @apiNote 1008 * This method also accepts a single array as an argument. The element type of 1009 * the resulting list will be the component type of the array, and the size of 1010 * the list will be equal to the length of the array. To create a list with 1011 * a single element that is an array, do the following: 1012 * 1013 * <pre>{@code 1014 * String[] array = ... ; 1015 * List<String[]> list = List.<String[]>of(array); 1016 * }</pre> 1017 * 1018 * This will cause the {@link List#of(Object) List.of(E)} method 1019 * to be invoked instead. 1020 * 1021 * @param <E> the {@code List}'s element type 1022 * @param elements the elements to be contained in the list 1023 * @return a {@code List} containing the specified elements 1024 * @throws NullPointerException if an element is {@code null} or if the array is {@code null} 1025 * 1026 * @since 9 1027 */ 1028 @SafeVarargs 1029 @SuppressWarnings("varargs") 1030 static <E> List<E> of(E... elements) { 1031 switch (elements.length) { // implicit null check of elements 1032 case 0: 1033 return ImmutableCollections.List0.instance(); 1034 case 1: 1035 return new ImmutableCollections.List1<>(elements[0]); 1036 case 2: 1037 return new ImmutableCollections.List2<>(elements[0], elements[1]); 1038 default: 1039 return new ImmutableCollections.ListN<>(elements); 1040 } 1041 } 1042 1043 /** 1044 * Returns an <a href="#unmodifiable">unmodifiable List</a> containing the elements 1045 * of the given Collection, in iteration order. The given Collection must not be null, 1046 * and it must not contain any null elements. If the given Collection is subsequently 1047 * modified, the returned List will not reflect such modifications. 1048 * 1049 * @param <E> the {@code List}'s element type 1050 * @param coll the collection from which elements are drawn, must be non-null 1051 * @return the new {@code List} 1052 * @throws NullPointerException if coll is null, or if it contains any nulls 1053 * @since 10 1054 */ 1055 @SuppressWarnings("unchecked") 1056 static <E> List<E> copyOf(Collection<? extends E> coll) { 1057 if (coll instanceof ImmutableCollections.AbstractImmutableList) { 1058 return (List<E>)coll; 1059 } else { 1060 return (List<E>)List.of(coll.toArray()); 1061 } 1062 } 1063 }