1 /* 2 * Copyright (c) 1997, 2013, 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.Consumer; 29 import java.util.function.Predicate; 30 import java.util.function.UnaryOperator; 31 32 /** 33 * Resizable-array implementation of the {@code List} interface. Implements 34 * all optional list operations, and permits all elements, including 35 * {@code null}. In addition to implementing the {@code List} interface, 36 * this class provides methods to manipulate the size of the array that is 37 * used internally to store the list. (This class is roughly equivalent to 38 * {@code Vector}, except that it is unsynchronized.) 39 * 40 * <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set}, 41 * {@code iterator}, and {@code listIterator} operations run in constant 42 * time. The {@code add} operation runs in <i>amortized constant time</i>, 43 * that is, adding n elements requires O(n) time. All of the other operations 44 * run in linear time (roughly speaking). The constant factor is low compared 45 * to that for the {@code LinkedList} implementation. 46 * 47 * <p>Each {@code ArrayList} instance has a <i>capacity</i>. The capacity is 48 * the size of the array used to store the elements in the list. It is always 49 * at least as large as the list size. As elements are added to an ArrayList, 50 * its capacity grows automatically. The details of the growth policy are not 51 * specified beyond the fact that adding an element has constant amortized 52 * time cost. 53 * 54 * <p>An application can increase the capacity of an {@code ArrayList} instance 55 * before adding a large number of elements using the {@code ensureCapacity} 56 * operation. This may reduce the amount of incremental reallocation. 57 * 58 * <p><strong>Note that this implementation is not synchronized.</strong> 59 * If multiple threads access an {@code ArrayList} instance concurrently, 60 * and at least one of the threads modifies the list structurally, it 61 * <i>must</i> be synchronized externally. (A structural modification is 62 * any operation that adds or deletes one or more elements, or explicitly 63 * resizes the backing array; merely setting the value of an element is not 64 * a structural modification.) This is typically accomplished by 65 * synchronizing on some object that naturally encapsulates the list. 66 * 67 * If no such object exists, the list should be "wrapped" using the 68 * {@link Collections#synchronizedList Collections.synchronizedList} 69 * method. This is best done at creation time, to prevent accidental 70 * unsynchronized access to the list:<pre> 71 * List list = Collections.synchronizedList(new ArrayList(...));</pre> 72 * 73 * <p id="fail-fast"> 74 * The iterators returned by this class's {@link #iterator() iterator} and 75 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>: 76 * if the list is structurally modified at any time after the iterator is 77 * created, in any way except through the iterator's own 78 * {@link ListIterator#remove() remove} or 79 * {@link ListIterator#add(Object) add} methods, the iterator will throw a 80 * {@link ConcurrentModificationException}. Thus, in the face of 81 * concurrent modification, the iterator fails quickly and cleanly, rather 82 * than risking arbitrary, non-deterministic behavior at an undetermined 83 * time in the future. 84 * 85 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 86 * as it is, generally speaking, impossible to make any hard guarantees in the 87 * presence of unsynchronized concurrent modification. Fail-fast iterators 88 * throw {@code ConcurrentModificationException} on a best-effort basis. 89 * Therefore, it would be wrong to write a program that depended on this 90 * exception for its correctness: <i>the fail-fast behavior of iterators 91 * should be used only to detect bugs.</i> 92 * 93 * <p>This class is a member of the 94 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 95 * Java Collections Framework</a>. 96 * 97 * @param <E> the type of elements in this list 98 * 99 * @author Josh Bloch 100 * @author Neal Gafter 101 * @see Collection 102 * @see List 103 * @see LinkedList 104 * @see Vector 105 * @since 1.2 106 */ 107 108 public class ArrayList<E> extends AbstractList<E> 109 implements List<E>, RandomAccess, Cloneable, java.io.Serializable 110 { 111 private static final long serialVersionUID = 8683452581122892189L; 112 113 /** 114 * Default initial capacity. 115 */ 116 private static final int DEFAULT_CAPACITY = 10; 117 118 /** 119 * Shared empty array instance used for empty instances. 120 */ 121 private static final Object[] EMPTY_ELEMENTDATA = {}; 122 123 /** 124 * Shared empty array instance used for default sized empty instances. We 125 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when 126 * first element is added. 127 */ 128 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; 129 130 /** 131 * The array buffer into which the elements of the ArrayList are stored. 132 * The capacity of the ArrayList is the length of this array buffer. Any 133 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA 134 * will be expanded to DEFAULT_CAPACITY when the first element is added. 135 */ 136 transient Object[] elementData; // non-private to simplify nested class access 137 138 /** 139 * The size of the ArrayList (the number of elements it contains). 140 * 141 * @serial 142 */ 143 private int size; 144 145 /** 146 * Constructs an empty list with the specified initial capacity. 147 * 148 * @param initialCapacity the initial capacity of the list 149 * @throws IllegalArgumentException if the specified initial capacity 150 * is negative 151 */ 152 public ArrayList(int initialCapacity) { 153 if (initialCapacity > 0) { 154 this.elementData = new Object[initialCapacity]; 155 } else if (initialCapacity == 0) { 156 this.elementData = EMPTY_ELEMENTDATA; 157 } else { 158 throw new IllegalArgumentException("Illegal Capacity: "+ 159 initialCapacity); 160 } 161 } 162 163 /** 164 * Constructs an empty list with an initial capacity of ten. 165 */ 166 public ArrayList() { 167 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA; 168 } 169 170 /** 171 * Constructs a list containing the elements of the specified 172 * collection, in the order they are returned by the collection's 173 * iterator. 174 * 175 * @param c the collection whose elements are to be placed into this list 176 * @throws NullPointerException if the specified collection is null 177 */ 178 public ArrayList(Collection<? extends E> c) { 179 elementData = c.toArray(); 180 if ((size = elementData.length) != 0) { 181 // c.toArray might (incorrectly) not return Object[] (see 6260652) 182 if (elementData.getClass() != Object[].class) 183 elementData = Arrays.copyOf(elementData, size, Object[].class); 184 } else { 185 // replace with empty array. 186 this.elementData = EMPTY_ELEMENTDATA; 187 } 188 } 189 190 /** 191 * Trims the capacity of this {@code ArrayList} instance to be the 192 * list's current size. An application can use this operation to minimize 193 * the storage of an {@code ArrayList} instance. 194 */ 195 public void trimToSize() { 196 modCount++; 197 if (size < elementData.length) { 198 elementData = (size == 0) 199 ? EMPTY_ELEMENTDATA 200 : Arrays.copyOf(elementData, size); 201 } 202 } 203 204 /** 205 * Increases the capacity of this {@code ArrayList} instance, if 206 * necessary, to ensure that it can hold at least the number of elements 207 * specified by the minimum capacity argument. 208 * 209 * @param minCapacity the desired minimum capacity 210 */ 211 public void ensureCapacity(int minCapacity) { 212 int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) 213 // any size if not default element table 214 ? 0 215 // larger than default for default empty table. It's already 216 // supposed to be at default size. 217 : DEFAULT_CAPACITY; 218 219 if (minCapacity > minExpand) { 220 ensureExplicitCapacity(minCapacity); 221 } 222 } 223 224 private void ensureCapacityInternal(int minCapacity) { 225 if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) { 226 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); 227 } 228 229 ensureExplicitCapacity(minCapacity); 230 } 231 232 private void ensureExplicitCapacity(int minCapacity) { 233 modCount++; 234 235 // overflow-conscious code 236 if (minCapacity - elementData.length > 0) 237 grow(minCapacity); 238 } 239 240 /** 241 * The maximum size of array to allocate. 242 * Some VMs reserve some header words in an array. 243 * Attempts to allocate larger arrays may result in 244 * OutOfMemoryError: Requested array size exceeds VM limit 245 */ 246 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; 247 248 /** 249 * Increases the capacity to ensure that it can hold at least the 250 * number of elements specified by the minimum capacity argument. 251 * 252 * @param minCapacity the desired minimum capacity 253 */ 254 private void grow(int minCapacity) { 255 // overflow-conscious code 256 int oldCapacity = elementData.length; 257 int newCapacity = oldCapacity + (oldCapacity >> 1); 258 if (newCapacity - minCapacity < 0) 259 newCapacity = minCapacity; 260 if (newCapacity - MAX_ARRAY_SIZE > 0) 261 newCapacity = hugeCapacity(minCapacity); 262 // minCapacity is usually close to size, so this is a win: 263 elementData = Arrays.copyOf(elementData, newCapacity); 264 } 265 266 private static int hugeCapacity(int minCapacity) { 267 if (minCapacity < 0) // overflow 268 throw new OutOfMemoryError(); 269 return (minCapacity > MAX_ARRAY_SIZE) ? 270 Integer.MAX_VALUE : 271 MAX_ARRAY_SIZE; 272 } 273 274 /** 275 * Returns the number of elements in this list. 276 * 277 * @return the number of elements in this list 278 */ 279 public int size() { 280 return size; 281 } 282 283 /** 284 * Returns {@code true} if this list contains no elements. 285 * 286 * @return {@code true} if this list contains no elements 287 */ 288 public boolean isEmpty() { 289 return size == 0; 290 } 291 292 /** 293 * Returns {@code true} if this list contains the specified element. 294 * More formally, returns {@code true} if and only if this list contains 295 * at least one element {@code e} such that 296 * <tt>(o==null ? e==null : o.equals(e))</tt>. 297 * 298 * @param o element whose presence in this list is to be tested 299 * @return {@code true} if this list contains the specified element 300 */ 301 public boolean contains(Object o) { 302 return indexOf(o) >= 0; 303 } 304 305 /** 306 * Returns the index of the first occurrence of the specified element 307 * in this list, or -1 if this list does not contain the element. 308 * More formally, returns the lowest index {@code i} such that 309 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 310 * or -1 if there is no such index. 311 */ 312 public int indexOf(Object o) { 313 if (o == null) { 314 for (int i = 0; i < size; i++) 315 if (elementData[i]==null) 316 return i; 317 } else { 318 for (int i = 0; i < size; i++) 319 if (o.equals(elementData[i])) 320 return i; 321 } 322 return -1; 323 } 324 325 /** 326 * Returns the index of the last occurrence of the specified element 327 * in this list, or -1 if this list does not contain the element. 328 * More formally, returns the highest index {@code i} such that 329 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 330 * or -1 if there is no such index. 331 */ 332 public int lastIndexOf(Object o) { 333 if (o == null) { 334 for (int i = size-1; i >= 0; i--) 335 if (elementData[i]==null) 336 return i; 337 } else { 338 for (int i = size-1; i >= 0; i--) 339 if (o.equals(elementData[i])) 340 return i; 341 } 342 return -1; 343 } 344 345 /** 346 * Returns a shallow copy of this {@code ArrayList} instance. (The 347 * elements themselves are not copied.) 348 * 349 * @return a clone of this {@code ArrayList} instance 350 */ 351 public Object clone() { 352 try { 353 ArrayList<?> v = (ArrayList<?>) super.clone(); 354 v.elementData = Arrays.copyOf(elementData, size); 355 v.modCount = 0; 356 return v; 357 } catch (CloneNotSupportedException e) { 358 // this shouldn't happen, since we are Cloneable 359 throw new InternalError(e); 360 } 361 } 362 363 /** 364 * Returns an array containing all of the elements in this list 365 * in proper sequence (from first to last element). 366 * 367 * <p>The returned array will be "safe" in that no references to it are 368 * maintained by this list. (In other words, this method must allocate 369 * a new array). The caller is thus free to modify the returned array. 370 * 371 * <p>This method acts as bridge between array-based and collection-based 372 * APIs. 373 * 374 * @return an array containing all of the elements in this list in 375 * proper sequence 376 */ 377 public Object[] toArray() { 378 return Arrays.copyOf(elementData, size); 379 } 380 381 /** 382 * Returns an array containing all of the elements in this list in proper 383 * sequence (from first to last element); the runtime type of the returned 384 * array is that of the specified array. If the list fits in the 385 * specified array, it is returned therein. Otherwise, a new array is 386 * allocated with the runtime type of the specified array and the size of 387 * this list. 388 * 389 * <p>If the list fits in the specified array with room to spare 390 * (i.e., the array has more elements than the list), the element in 391 * the array immediately following the end of the collection is set to 392 * {@code null}. (This is useful in determining the length of the 393 * list <i>only</i> if the caller knows that the list does not contain 394 * any null elements.) 395 * 396 * @param a the array into which the elements of the list are to 397 * be stored, if it is big enough; otherwise, a new array of the 398 * same runtime type is allocated for this purpose. 399 * @return an array containing the elements of the list 400 * @throws ArrayStoreException if the runtime type of the specified array 401 * is not a supertype of the runtime type of every element in 402 * this list 403 * @throws NullPointerException if the specified array is null 404 */ 405 @SuppressWarnings("unchecked") 406 public <T> T[] toArray(T[] a) { 407 if (a.length < size) 408 // Make a new array of a's runtime type, but my contents: 409 return (T[]) Arrays.copyOf(elementData, size, a.getClass()); 410 System.arraycopy(elementData, 0, a, 0, size); 411 if (a.length > size) 412 a[size] = null; 413 return a; 414 } 415 416 // Positional Access Operations 417 418 @SuppressWarnings("unchecked") 419 E elementData(int index) { 420 return (E) elementData[index]; 421 } 422 423 /** 424 * Returns the element at the specified position in this list. 425 * 426 * @param index index of the element to return 427 * @return the element at the specified position in this list 428 * @throws IndexOutOfBoundsException {@inheritDoc} 429 */ 430 public E get(int index) { 431 rangeCheck(index); 432 433 return elementData(index); 434 } 435 436 /** 437 * Replaces the element at the specified position in this list with 438 * the specified element. 439 * 440 * @param index index of the element to replace 441 * @param element element to be stored at the specified position 442 * @return the element previously at the specified position 443 * @throws IndexOutOfBoundsException {@inheritDoc} 444 */ 445 public E set(int index, E element) { 446 rangeCheck(index); 447 448 E oldValue = elementData(index); 449 elementData[index] = element; 450 return oldValue; 451 } 452 453 /** 454 * Appends the specified element to the end of this list. 455 * 456 * @param e element to be appended to this list 457 * @return {@code true} (as specified by {@link Collection#add}) 458 */ 459 public boolean add(E e) { 460 ensureCapacityInternal(size + 1); // Increments modCount!! 461 elementData[size++] = e; 462 return true; 463 } 464 465 /** 466 * Inserts the specified element at the specified position in this 467 * list. Shifts the element currently at that position (if any) and 468 * any subsequent elements to the right (adds one to their indices). 469 * 470 * @param index index at which the specified element is to be inserted 471 * @param element element to be inserted 472 * @throws IndexOutOfBoundsException {@inheritDoc} 473 */ 474 public void add(int index, E element) { 475 rangeCheckForAdd(index); 476 477 ensureCapacityInternal(size + 1); // Increments modCount!! 478 System.arraycopy(elementData, index, elementData, index + 1, 479 size - index); 480 elementData[index] = element; 481 size++; 482 } 483 484 /** 485 * Removes the element at the specified position in this list. 486 * Shifts any subsequent elements to the left (subtracts one from their 487 * indices). 488 * 489 * @param index the index of the element to be removed 490 * @return the element that was removed from the list 491 * @throws IndexOutOfBoundsException {@inheritDoc} 492 */ 493 public E remove(int index) { 494 rangeCheck(index); 495 496 modCount++; 497 E oldValue = elementData(index); 498 499 int numMoved = size - index - 1; 500 if (numMoved > 0) 501 System.arraycopy(elementData, index+1, elementData, index, 502 numMoved); 503 elementData[--size] = null; // clear to let GC do its work 504 505 return oldValue; 506 } 507 508 /** 509 * Removes the first occurrence of the specified element from this list, 510 * if it is present. If the list does not contain the element, it is 511 * unchanged. More formally, removes the element with the lowest index 512 * {@code i} such that 513 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> 514 * (if such an element exists). Returns {@code true} if this list 515 * contained the specified element (or equivalently, if this list 516 * changed as a result of the call). 517 * 518 * @param o element to be removed from this list, if present 519 * @return {@code true} if this list contained the specified element 520 */ 521 public boolean remove(Object o) { 522 if (o == null) { 523 for (int index = 0; index < size; index++) 524 if (elementData[index] == null) { 525 fastRemove(index); 526 return true; 527 } 528 } else { 529 for (int index = 0; index < size; index++) 530 if (o.equals(elementData[index])) { 531 fastRemove(index); 532 return true; 533 } 534 } 535 return false; 536 } 537 538 /* 539 * Private remove method that skips bounds checking and does not 540 * return the value removed. 541 */ 542 private void fastRemove(int index) { 543 modCount++; 544 int numMoved = size - index - 1; 545 if (numMoved > 0) 546 System.arraycopy(elementData, index+1, elementData, index, 547 numMoved); 548 elementData[--size] = null; // clear to let GC do its work 549 } 550 551 /** 552 * Removes all of the elements from this list. The list will 553 * be empty after this call returns. 554 */ 555 public void clear() { 556 modCount++; 557 558 // clear to let GC do its work 559 for (int i = 0; i < size; i++) 560 elementData[i] = null; 561 562 size = 0; 563 } 564 565 /** 566 * Appends all of the elements in the specified collection to the end of 567 * this list, in the order that they are returned by the 568 * specified collection's Iterator. The behavior of this operation is 569 * undefined if the specified collection is modified while the operation 570 * is in progress. (This implies that the behavior of this call is 571 * undefined if the specified collection is this list, and this 572 * list is nonempty.) 573 * 574 * @param c collection containing elements to be added to this list 575 * @return {@code true} if this list changed as a result of the call 576 * @throws NullPointerException if the specified collection is null 577 */ 578 public boolean addAll(Collection<? extends E> c) { 579 Object[] a = c.toArray(); 580 int numNew = a.length; 581 ensureCapacityInternal(size + numNew); // Increments modCount 582 System.arraycopy(a, 0, elementData, size, numNew); 583 size += numNew; 584 return numNew != 0; 585 } 586 587 /** 588 * Inserts all of the elements in the specified collection into this 589 * list, starting at the specified position. Shifts the element 590 * currently at that position (if any) and any subsequent elements to 591 * the right (increases their indices). The new elements will appear 592 * in the list in the order that they are returned by the 593 * specified collection's iterator. 594 * 595 * @param index index at which to insert the first element from the 596 * specified collection 597 * @param c collection containing elements to be added to this list 598 * @return {@code true} if this list changed as a result of the call 599 * @throws IndexOutOfBoundsException {@inheritDoc} 600 * @throws NullPointerException if the specified collection is null 601 */ 602 public boolean addAll(int index, Collection<? extends E> c) { 603 rangeCheckForAdd(index); 604 605 Object[] a = c.toArray(); 606 int numNew = a.length; 607 ensureCapacityInternal(size + numNew); // Increments modCount 608 609 int numMoved = size - index; 610 if (numMoved > 0) 611 System.arraycopy(elementData, index, elementData, index + numNew, 612 numMoved); 613 614 System.arraycopy(a, 0, elementData, index, numNew); 615 size += numNew; 616 return numNew != 0; 617 } 618 619 /** 620 * Removes from this list all of the elements whose index is between 621 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. 622 * Shifts any succeeding elements to the left (reduces their index). 623 * This call shortens the list by {@code (toIndex - fromIndex)} elements. 624 * (If {@code toIndex==fromIndex}, this operation has no effect.) 625 * 626 * @throws IndexOutOfBoundsException if {@code fromIndex} or 627 * {@code toIndex} is out of range 628 * ({@code fromIndex < 0 || 629 * toIndex > size() || 630 * toIndex < fromIndex}) 631 */ 632 protected void removeRange(int fromIndex, int toIndex) { 633 if (fromIndex > toIndex) { 634 throw new IndexOutOfBoundsException( 635 outOfBoundsMsg(fromIndex, toIndex)); 636 } 637 modCount++; 638 int numMoved = size - toIndex; 639 System.arraycopy(elementData, toIndex, elementData, fromIndex, 640 numMoved); 641 642 // clear to let GC do its work 643 int newSize = size - (toIndex-fromIndex); 644 for (int i = newSize; i < size; i++) { 645 elementData[i] = null; 646 } 647 size = newSize; 648 } 649 650 /** 651 * Checks if the given index is in range. If not, throws an appropriate 652 * runtime exception. This method does *not* check if the index is 653 * negative: It is always used immediately prior to an array access, 654 * which throws an ArrayIndexOutOfBoundsException if index is negative. 655 */ 656 private void rangeCheck(int index) { 657 if (index >= size) 658 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 659 } 660 661 /** 662 * A version of rangeCheck used by add and addAll. 663 */ 664 private void rangeCheckForAdd(int index) { 665 if (index > size || index < 0) 666 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 667 } 668 669 /** 670 * Constructs an IndexOutOfBoundsException detail message. 671 * Of the many possible refactorings of the error handling code, 672 * this "outlining" performs best with both server and client VMs. 673 */ 674 private String outOfBoundsMsg(int index) { 675 return "Index: "+index+", Size: "+size; 676 } 677 678 /** 679 * A version used in checking (fromIndex > toIndex) condition 680 */ 681 private static String outOfBoundsMsg(int fromIndex, int toIndex) { 682 return "From Index: " + fromIndex + " > To Index: " + toIndex; 683 } 684 685 /** 686 * Removes from this list all of its elements that are contained in the 687 * specified collection. 688 * 689 * @param c collection containing elements to be removed from this list 690 * @return {@code true} if this list changed as a result of the call 691 * @throws ClassCastException if the class of an element of this list 692 * is incompatible with the specified collection 693 * (<a href="Collection.html#optional-restrictions">optional</a>) 694 * @throws NullPointerException if this list contains a null element and the 695 * specified collection does not permit null elements 696 * (<a href="Collection.html#optional-restrictions">optional</a>), 697 * or if the specified collection is null 698 * @see Collection#contains(Object) 699 */ 700 public boolean removeAll(Collection<?> c) { 701 Objects.requireNonNull(c); 702 return batchRemove(c, false); 703 } 704 705 /** 706 * Retains only the elements in this list that are contained in the 707 * specified collection. In other words, removes from this list all 708 * of its elements that are not contained in the specified collection. 709 * 710 * @param c collection containing elements to be retained in this list 711 * @return {@code true} if this list changed as a result of the call 712 * @throws ClassCastException if the class of an element of this list 713 * is incompatible with the specified collection 714 * (<a href="Collection.html#optional-restrictions">optional</a>) 715 * @throws NullPointerException if this list contains a null element and the 716 * specified collection does not permit null elements 717 * (<a href="Collection.html#optional-restrictions">optional</a>), 718 * or if the specified collection is null 719 * @see Collection#contains(Object) 720 */ 721 public boolean retainAll(Collection<?> c) { 722 Objects.requireNonNull(c); 723 return batchRemove(c, true); 724 } 725 726 private boolean batchRemove(Collection<?> c, boolean complement) { 727 final Object[] elementData = this.elementData; 728 int r = 0, w = 0; 729 boolean modified = false; 730 try { 731 for (; r < size; r++) 732 if (c.contains(elementData[r]) == complement) 733 elementData[w++] = elementData[r]; 734 } finally { 735 // Preserve behavioral compatibility with AbstractCollection, 736 // even if c.contains() throws. 737 if (r != size) { 738 System.arraycopy(elementData, r, 739 elementData, w, 740 size - r); 741 w += size - r; 742 } 743 if (w != size) { 744 // clear to let GC do its work 745 for (int i = w; i < size; i++) 746 elementData[i] = null; 747 modCount += size - w; 748 size = w; 749 modified = true; 750 } 751 } 752 return modified; 753 } 754 755 /** 756 * Save the state of the {@code ArrayList} instance to a stream (that 757 * is, serialize it). 758 * 759 * @serialData The length of the array backing the {@code ArrayList} 760 * instance is emitted (int), followed by all of its elements 761 * (each an {@code Object}) in the proper order. 762 */ 763 private void writeObject(java.io.ObjectOutputStream s) 764 throws java.io.IOException{ 765 // Write out element count, and any hidden stuff 766 int expectedModCount = modCount; 767 s.defaultWriteObject(); 768 769 // Write out size as capacity for behavioural compatibility with clone() 770 s.writeInt(size); 771 772 // Write out all elements in the proper order. 773 for (int i=0; i<size; i++) { 774 s.writeObject(elementData[i]); 775 } 776 777 if (modCount != expectedModCount) { 778 throw new ConcurrentModificationException(); 779 } 780 } 781 782 /** 783 * Reconstitute the {@code ArrayList} instance from a stream (that is, 784 * deserialize it). 785 */ 786 private void readObject(java.io.ObjectInputStream s) 787 throws java.io.IOException, ClassNotFoundException { 788 elementData = EMPTY_ELEMENTDATA; 789 790 // Read in size, and any hidden stuff 791 s.defaultReadObject(); 792 793 // Read in capacity 794 s.readInt(); // ignored 795 796 if (size > 0) { 797 // be like clone(), allocate array based upon size not capacity 798 ensureCapacityInternal(size); 799 800 Object[] a = elementData; 801 // Read in all elements in the proper order. 802 for (int i=0; i<size; i++) { 803 a[i] = s.readObject(); 804 } 805 } 806 } 807 808 /** 809 * Returns a list iterator over the elements in this list (in proper 810 * sequence), starting at the specified position in the list. 811 * The specified index indicates the first element that would be 812 * returned by an initial call to {@link ListIterator#next next}. 813 * An initial call to {@link ListIterator#previous previous} would 814 * return the element with the specified index minus one. 815 * 816 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>. 817 * 818 * @throws IndexOutOfBoundsException {@inheritDoc} 819 */ 820 public ListIterator<E> listIterator(int index) { 821 if (index < 0 || index > size) 822 throw new IndexOutOfBoundsException("Index: "+index); 823 return new ListItr(index); 824 } 825 826 /** 827 * Returns a list iterator over the elements in this list (in proper 828 * sequence). 829 * 830 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>. 831 * 832 * @see #listIterator(int) 833 */ 834 public ListIterator<E> listIterator() { 835 return new ListItr(0); 836 } 837 838 /** 839 * Returns an iterator over the elements in this list in proper sequence. 840 * 841 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>. 842 * 843 * @return an iterator over the elements in this list in proper sequence 844 */ 845 public Iterator<E> iterator() { 846 return new Itr(); 847 } 848 849 /** 850 * An optimized version of AbstractList.Itr 851 */ 852 private class Itr implements Iterator<E> { 853 int cursor; // index of next element to return 854 int lastRet = -1; // index of last element returned; -1 if no such 855 int expectedModCount = modCount; 856 857 public boolean hasNext() { 858 return cursor != size; 859 } 860 861 @SuppressWarnings("unchecked") 862 public E next() { 863 checkForComodification(); 864 int i = cursor; 865 if (i >= size) 866 throw new NoSuchElementException(); 867 Object[] elementData = ArrayList.this.elementData; 868 if (i >= elementData.length) 869 throw new ConcurrentModificationException(); 870 cursor = i + 1; 871 return (E) elementData[lastRet = i]; 872 } 873 874 public void remove() { 875 if (lastRet < 0) 876 throw new IllegalStateException(); 877 checkForComodification(); 878 879 try { 880 ArrayList.this.remove(lastRet); 881 cursor = lastRet; 882 lastRet = -1; 883 expectedModCount = modCount; 884 } catch (IndexOutOfBoundsException ex) { 885 throw new ConcurrentModificationException(); 886 } 887 } 888 889 @Override 890 @SuppressWarnings("unchecked") 891 public void forEachRemaining(Consumer<? super E> consumer) { 892 Objects.requireNonNull(consumer); 893 final int size = ArrayList.this.size; 894 int i = cursor; 895 if (i >= size) { 896 return; 897 } 898 final Object[] elementData = ArrayList.this.elementData; 899 if (i >= elementData.length) { 900 throw new ConcurrentModificationException(); 901 } 902 while (i != size && modCount == expectedModCount) { 903 consumer.accept((E) elementData[i++]); 904 } 905 // update once at end of iteration to reduce heap write traffic 906 cursor = i; 907 lastRet = i - 1; 908 checkForComodification(); 909 } 910 911 final void checkForComodification() { 912 if (modCount != expectedModCount) 913 throw new ConcurrentModificationException(); 914 } 915 } 916 917 /** 918 * An optimized version of AbstractList.ListItr 919 */ 920 private class ListItr extends Itr implements ListIterator<E> { 921 ListItr(int index) { 922 super(); 923 cursor = index; 924 } 925 926 public boolean hasPrevious() { 927 return cursor != 0; 928 } 929 930 public int nextIndex() { 931 return cursor; 932 } 933 934 public int previousIndex() { 935 return cursor - 1; 936 } 937 938 @SuppressWarnings("unchecked") 939 public E previous() { 940 checkForComodification(); 941 int i = cursor - 1; 942 if (i < 0) 943 throw new NoSuchElementException(); 944 Object[] elementData = ArrayList.this.elementData; 945 if (i >= elementData.length) 946 throw new ConcurrentModificationException(); 947 cursor = i; 948 return (E) elementData[lastRet = i]; 949 } 950 951 public void set(E e) { 952 if (lastRet < 0) 953 throw new IllegalStateException(); 954 checkForComodification(); 955 956 try { 957 ArrayList.this.set(lastRet, e); 958 } catch (IndexOutOfBoundsException ex) { 959 throw new ConcurrentModificationException(); 960 } 961 } 962 963 public void add(E e) { 964 checkForComodification(); 965 966 try { 967 int i = cursor; 968 ArrayList.this.add(i, e); 969 cursor = i + 1; 970 lastRet = -1; 971 expectedModCount = modCount; 972 } catch (IndexOutOfBoundsException ex) { 973 throw new ConcurrentModificationException(); 974 } 975 } 976 } 977 978 /** 979 * Returns a view of the portion of this list between the specified 980 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If 981 * {@code fromIndex} and {@code toIndex} are equal, the returned list is 982 * empty.) The returned list is backed by this list, so non-structural 983 * changes in the returned list are reflected in this list, and vice-versa. 984 * The returned list supports all of the optional list operations. 985 * 986 * <p>This method eliminates the need for explicit range operations (of 987 * the sort that commonly exist for arrays). Any operation that expects 988 * a list can be used as a range operation by passing a subList view 989 * instead of a whole list. For example, the following idiom 990 * removes a range of elements from a list: 991 * <pre> 992 * list.subList(from, to).clear(); 993 * </pre> 994 * Similar idioms may be constructed for {@link #indexOf(Object)} and 995 * {@link #lastIndexOf(Object)}, and all of the algorithms in the 996 * {@link Collections} class can be applied to a subList. 997 * 998 * <p>The semantics of the list returned by this method become undefined if 999 * the backing list (i.e., this list) is <i>structurally modified</i> in 1000 * any way other than via the returned list. (Structural modifications are 1001 * those that change the size of this list, or otherwise perturb it in such 1002 * a fashion that iterations in progress may yield incorrect results.) 1003 * 1004 * @throws IndexOutOfBoundsException {@inheritDoc} 1005 * @throws IllegalArgumentException {@inheritDoc} 1006 */ 1007 public List<E> subList(int fromIndex, int toIndex) { 1008 subListRangeCheck(fromIndex, toIndex, size); 1009 return new SubList(this, 0, fromIndex, toIndex); 1010 } 1011 1012 static void subListRangeCheck(int fromIndex, int toIndex, int size) { 1013 if (fromIndex < 0) 1014 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 1015 if (toIndex > size) 1016 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 1017 if (fromIndex > toIndex) 1018 throw new IllegalArgumentException("fromIndex(" + fromIndex + 1019 ") > toIndex(" + toIndex + ")"); 1020 } 1021 1022 private class SubList extends AbstractList<E> implements RandomAccess { 1023 private final AbstractList<E> parent; 1024 private final int parentOffset; 1025 private final int offset; 1026 int size; 1027 1028 SubList(AbstractList<E> parent, 1029 int offset, int fromIndex, int toIndex) { 1030 this.parent = parent; 1031 this.parentOffset = fromIndex; 1032 this.offset = offset + fromIndex; 1033 this.size = toIndex - fromIndex; 1034 this.modCount = ArrayList.this.modCount; 1035 } 1036 1037 public E set(int index, E e) { 1038 rangeCheck(index); 1039 checkForComodification(); 1040 E oldValue = ArrayList.this.elementData(offset + index); 1041 ArrayList.this.elementData[offset + index] = e; 1042 return oldValue; 1043 } 1044 1045 public E get(int index) { 1046 rangeCheck(index); 1047 checkForComodification(); 1048 return ArrayList.this.elementData(offset + index); 1049 } 1050 1051 public int size() { 1052 checkForComodification(); 1053 return this.size; 1054 } 1055 1056 public void add(int index, E e) { 1057 rangeCheckForAdd(index); 1058 checkForComodification(); 1059 parent.add(parentOffset + index, e); 1060 this.modCount = parent.modCount; 1061 this.size++; 1062 } 1063 1064 public E remove(int index) { 1065 rangeCheck(index); 1066 checkForComodification(); 1067 E result = parent.remove(parentOffset + index); 1068 this.modCount = parent.modCount; 1069 this.size--; 1070 return result; 1071 } 1072 1073 protected void removeRange(int fromIndex, int toIndex) { 1074 checkForComodification(); 1075 parent.removeRange(parentOffset + fromIndex, 1076 parentOffset + toIndex); 1077 this.modCount = parent.modCount; 1078 this.size -= toIndex - fromIndex; 1079 } 1080 1081 public boolean addAll(Collection<? extends E> c) { 1082 return addAll(this.size, c); 1083 } 1084 1085 public boolean addAll(int index, Collection<? extends E> c) { 1086 rangeCheckForAdd(index); 1087 int cSize = c.size(); 1088 if (cSize==0) 1089 return false; 1090 1091 checkForComodification(); 1092 parent.addAll(parentOffset + index, c); 1093 this.modCount = parent.modCount; 1094 this.size += cSize; 1095 return true; 1096 } 1097 1098 public Iterator<E> iterator() { 1099 return listIterator(); 1100 } 1101 1102 public ListIterator<E> listIterator(final int index) { 1103 checkForComodification(); 1104 rangeCheckForAdd(index); 1105 final int offset = this.offset; 1106 1107 return new ListIterator<E>() { 1108 int cursor = index; 1109 int lastRet = -1; 1110 int expectedModCount = ArrayList.this.modCount; 1111 1112 public boolean hasNext() { 1113 return cursor != SubList.this.size; 1114 } 1115 1116 @SuppressWarnings("unchecked") 1117 public E next() { 1118 checkForComodification(); 1119 int i = cursor; 1120 if (i >= SubList.this.size) 1121 throw new NoSuchElementException(); 1122 Object[] elementData = ArrayList.this.elementData; 1123 if (offset + i >= elementData.length) 1124 throw new ConcurrentModificationException(); 1125 cursor = i + 1; 1126 return (E) elementData[offset + (lastRet = i)]; 1127 } 1128 1129 public boolean hasPrevious() { 1130 return cursor != 0; 1131 } 1132 1133 @SuppressWarnings("unchecked") 1134 public E previous() { 1135 checkForComodification(); 1136 int i = cursor - 1; 1137 if (i < 0) 1138 throw new NoSuchElementException(); 1139 Object[] elementData = ArrayList.this.elementData; 1140 if (offset + i >= elementData.length) 1141 throw new ConcurrentModificationException(); 1142 cursor = i; 1143 return (E) elementData[offset + (lastRet = i)]; 1144 } 1145 1146 @SuppressWarnings("unchecked") 1147 public void forEachRemaining(Consumer<? super E> consumer) { 1148 Objects.requireNonNull(consumer); 1149 final int size = SubList.this.size; 1150 int i = cursor; 1151 if (i >= size) { 1152 return; 1153 } 1154 final Object[] elementData = ArrayList.this.elementData; 1155 if (offset + i >= elementData.length) { 1156 throw new ConcurrentModificationException(); 1157 } 1158 while (i != size && modCount == expectedModCount) { 1159 consumer.accept((E) elementData[offset + (i++)]); 1160 } 1161 // update once at end of iteration to reduce heap write traffic 1162 lastRet = cursor = i; 1163 checkForComodification(); 1164 } 1165 1166 public int nextIndex() { 1167 return cursor; 1168 } 1169 1170 public int previousIndex() { 1171 return cursor - 1; 1172 } 1173 1174 public void remove() { 1175 if (lastRet < 0) 1176 throw new IllegalStateException(); 1177 checkForComodification(); 1178 1179 try { 1180 SubList.this.remove(lastRet); 1181 cursor = lastRet; 1182 lastRet = -1; 1183 expectedModCount = ArrayList.this.modCount; 1184 } catch (IndexOutOfBoundsException ex) { 1185 throw new ConcurrentModificationException(); 1186 } 1187 } 1188 1189 public void set(E e) { 1190 if (lastRet < 0) 1191 throw new IllegalStateException(); 1192 checkForComodification(); 1193 1194 try { 1195 ArrayList.this.set(offset + lastRet, e); 1196 } catch (IndexOutOfBoundsException ex) { 1197 throw new ConcurrentModificationException(); 1198 } 1199 } 1200 1201 public void add(E e) { 1202 checkForComodification(); 1203 1204 try { 1205 int i = cursor; 1206 SubList.this.add(i, e); 1207 cursor = i + 1; 1208 lastRet = -1; 1209 expectedModCount = ArrayList.this.modCount; 1210 } catch (IndexOutOfBoundsException ex) { 1211 throw new ConcurrentModificationException(); 1212 } 1213 } 1214 1215 final void checkForComodification() { 1216 if (expectedModCount != ArrayList.this.modCount) 1217 throw new ConcurrentModificationException(); 1218 } 1219 }; 1220 } 1221 1222 public List<E> subList(int fromIndex, int toIndex) { 1223 subListRangeCheck(fromIndex, toIndex, size); 1224 return new SubList(this, offset, fromIndex, toIndex); 1225 } 1226 1227 private void rangeCheck(int index) { 1228 if (index < 0 || index >= this.size) 1229 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1230 } 1231 1232 private void rangeCheckForAdd(int index) { 1233 if (index < 0 || index > this.size) 1234 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1235 } 1236 1237 private String outOfBoundsMsg(int index) { 1238 return "Index: "+index+", Size: "+this.size; 1239 } 1240 1241 private void checkForComodification() { 1242 if (ArrayList.this.modCount != this.modCount) 1243 throw new ConcurrentModificationException(); 1244 } 1245 1246 public Spliterator<E> spliterator() { 1247 checkForComodification(); 1248 return new ArrayListSpliterator<>(ArrayList.this, offset, 1249 offset + this.size, this.modCount); 1250 } 1251 } 1252 1253 @Override 1254 public void forEach(Consumer<? super E> action) { 1255 Objects.requireNonNull(action); 1256 final int expectedModCount = modCount; 1257 @SuppressWarnings("unchecked") 1258 final E[] elementData = (E[]) this.elementData; 1259 final int size = this.size; 1260 for (int i=0; modCount == expectedModCount && i < size; i++) { 1261 action.accept(elementData[i]); 1262 } 1263 if (modCount != expectedModCount) { 1264 throw new ConcurrentModificationException(); 1265 } 1266 } 1267 1268 /** 1269 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> 1270 * and <em>fail-fast</em> {@link Spliterator} over the elements in this 1271 * list. 1272 * 1273 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, 1274 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}. 1275 * Overriding implementations should document the reporting of additional 1276 * characteristic values. 1277 * 1278 * @return a {@code Spliterator} over the elements in this list 1279 * @since 1.8 1280 */ 1281 @Override 1282 public Spliterator<E> spliterator() { 1283 return new ArrayListSpliterator<>(this, 0, -1, 0); 1284 } 1285 1286 /** Index-based split-by-two, lazily initialized Spliterator */ 1287 static final class ArrayListSpliterator<E> implements Spliterator<E> { 1288 1289 /* 1290 * If ArrayLists were immutable, or structurally immutable (no 1291 * adds, removes, etc), we could implement their spliterators 1292 * with Arrays.spliterator. Instead we detect as much 1293 * interference during traversal as practical without 1294 * sacrificing much performance. We rely primarily on 1295 * modCounts. These are not guaranteed to detect concurrency 1296 * violations, and are sometimes overly conservative about 1297 * within-thread interference, but detect enough problems to 1298 * be worthwhile in practice. To carry this out, we (1) lazily 1299 * initialize fence and expectedModCount until the latest 1300 * point that we need to commit to the state we are checking 1301 * against; thus improving precision. (This doesn't apply to 1302 * SubLists, that create spliterators with current non-lazy 1303 * values). (2) We perform only a single 1304 * ConcurrentModificationException check at the end of forEach 1305 * (the most performance-sensitive method). When using forEach 1306 * (as opposed to iterators), we can normally only detect 1307 * interference after actions, not before. Further 1308 * CME-triggering checks apply to all other possible 1309 * violations of assumptions for example null or too-small 1310 * elementData array given its size(), that could only have 1311 * occurred due to interference. This allows the inner loop 1312 * of forEach to run without any further checks, and 1313 * simplifies lambda-resolution. While this does entail a 1314 * number of checks, note that in the common case of 1315 * list.stream().forEach(a), no checks or other computation 1316 * occur anywhere other than inside forEach itself. The other 1317 * less-often-used methods cannot take advantage of most of 1318 * these streamlinings. 1319 */ 1320 1321 private final ArrayList<E> list; 1322 private int index; // current index, modified on advance/split 1323 private int fence; // -1 until used; then one past last index 1324 private int expectedModCount; // initialized when fence set 1325 1326 /** Create new spliterator covering the given range */ 1327 ArrayListSpliterator(ArrayList<E> list, int origin, int fence, 1328 int expectedModCount) { 1329 this.list = list; // OK if null unless traversed 1330 this.index = origin; 1331 this.fence = fence; 1332 this.expectedModCount = expectedModCount; 1333 } 1334 1335 private int getFence() { // initialize fence to size on first use 1336 int hi; // (a specialized variant appears in method forEach) 1337 ArrayList<E> lst; 1338 if ((hi = fence) < 0) { 1339 if ((lst = list) == null) 1340 hi = fence = 0; 1341 else { 1342 expectedModCount = lst.modCount; 1343 hi = fence = lst.size; 1344 } 1345 } 1346 return hi; 1347 } 1348 1349 public ArrayListSpliterator<E> trySplit() { 1350 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1351 return (lo >= mid) ? null : // divide range in half unless too small 1352 new ArrayListSpliterator<>(list, lo, index = mid, 1353 expectedModCount); 1354 } 1355 1356 public boolean tryAdvance(Consumer<? super E> action) { 1357 if (action == null) 1358 throw new NullPointerException(); 1359 int hi = getFence(), i = index; 1360 if (i < hi) { 1361 index = i + 1; 1362 @SuppressWarnings("unchecked") E e = (E)list.elementData[i]; 1363 action.accept(e); 1364 if (list.modCount != expectedModCount) 1365 throw new ConcurrentModificationException(); 1366 return true; 1367 } 1368 return false; 1369 } 1370 1371 public void forEachRemaining(Consumer<? super E> action) { 1372 int i, hi, mc; // hoist accesses and checks from loop 1373 ArrayList<E> lst; Object[] a; 1374 if (action == null) 1375 throw new NullPointerException(); 1376 if ((lst = list) != null && (a = lst.elementData) != null) { 1377 if ((hi = fence) < 0) { 1378 mc = lst.modCount; 1379 hi = lst.size; 1380 } 1381 else 1382 mc = expectedModCount; 1383 if ((i = index) >= 0 && (index = hi) <= a.length) { 1384 for (; i < hi; ++i) { 1385 @SuppressWarnings("unchecked") E e = (E) a[i]; 1386 action.accept(e); 1387 } 1388 if (lst.modCount == mc) 1389 return; 1390 } 1391 } 1392 throw new ConcurrentModificationException(); 1393 } 1394 1395 public long estimateSize() { 1396 return (long) (getFence() - index); 1397 } 1398 1399 public int characteristics() { 1400 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED; 1401 } 1402 } 1403 1404 @Override 1405 public boolean removeIf(Predicate<? super E> filter) { 1406 Objects.requireNonNull(filter); 1407 // figure out which elements are to be removed 1408 // any exception thrown from the filter predicate at this stage 1409 // will leave the collection unmodified 1410 int removeCount = 0; 1411 final BitSet removeSet = new BitSet(size); 1412 final int expectedModCount = modCount; 1413 final int size = this.size; 1414 for (int i=0; modCount == expectedModCount && i < size; i++) { 1415 @SuppressWarnings("unchecked") 1416 final E element = (E) elementData[i]; 1417 if (filter.test(element)) { 1418 removeSet.set(i); 1419 removeCount++; 1420 } 1421 } 1422 if (modCount != expectedModCount) { 1423 throw new ConcurrentModificationException(); 1424 } 1425 1426 // shift surviving elements left over the spaces left by removed elements 1427 final boolean anyToRemove = removeCount > 0; 1428 if (anyToRemove) { 1429 final int newSize = size - removeCount; 1430 for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) { 1431 i = removeSet.nextClearBit(i); 1432 elementData[j] = elementData[i]; 1433 } 1434 for (int k=newSize; k < size; k++) { 1435 elementData[k] = null; // Let gc do its work 1436 } 1437 this.size = newSize; 1438 if (modCount != expectedModCount) { 1439 throw new ConcurrentModificationException(); 1440 } 1441 modCount++; 1442 } 1443 1444 return anyToRemove; 1445 } 1446 1447 @Override 1448 @SuppressWarnings("unchecked") 1449 public void replaceAll(UnaryOperator<E> operator) { 1450 Objects.requireNonNull(operator); 1451 final int expectedModCount = modCount; 1452 final int size = this.size; 1453 for (int i=0; modCount == expectedModCount && i < size; i++) { 1454 elementData[i] = operator.apply((E) elementData[i]); 1455 } 1456 if (modCount != expectedModCount) { 1457 throw new ConcurrentModificationException(); 1458 } 1459 modCount++; 1460 } 1461 1462 @Override 1463 @SuppressWarnings("unchecked") 1464 public void sort(Comparator<? super E> c) { 1465 final int expectedModCount = modCount; 1466 Arrays.sort((E[]) elementData, 0, size, c); 1467 if (modCount != expectedModCount) { 1468 throw new ConcurrentModificationException(); 1469 } 1470 modCount++; 1471 } 1472 }