ArrayList.java revision 8b056f0b15bc1e45da8d4c504353b05e681ac013
1/* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27package java.util; 28 29import java.util.function.Consumer; 30 31/** 32 * Resizable-array implementation of the <tt>List</tt> interface. Implements 33 * all optional list operations, and permits all elements, including 34 * <tt>null</tt>. In addition to implementing the <tt>List</tt> interface, 35 * this class provides methods to manipulate the size of the array that is 36 * used internally to store the list. (This class is roughly equivalent to 37 * <tt>Vector</tt>, except that it is unsynchronized.) 38 * 39 * <p>The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>, 40 * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant 41 * time. The <tt>add</tt> operation runs in <i>amortized constant time</i>, 42 * that is, adding n elements requires O(n) time. All of the other operations 43 * run in linear time (roughly speaking). The constant factor is low compared 44 * to that for the <tt>LinkedList</tt> implementation. 45 * 46 * <p>Each <tt>ArrayList</tt> instance has a <i>capacity</i>. The capacity is 47 * the size of the array used to store the elements in the list. It is always 48 * at least as large as the list size. As elements are added to an ArrayList, 49 * its capacity grows automatically. The details of the growth policy are not 50 * specified beyond the fact that adding an element has constant amortized 51 * time cost. 52 * 53 * <p>An application can increase the capacity of an <tt>ArrayList</tt> instance 54 * before adding a large number of elements using the <tt>ensureCapacity</tt> 55 * operation. This may reduce the amount of incremental reallocation. 56 * 57 * <p><strong>Note that this implementation is not synchronized.</strong> 58 * If multiple threads access an <tt>ArrayList</tt> instance concurrently, 59 * and at least one of the threads modifies the list structurally, it 60 * <i>must</i> be synchronized externally. (A structural modification is 61 * any operation that adds or deletes one or more elements, or explicitly 62 * resizes the backing array; merely setting the value of an element is not 63 * a structural modification.) This is typically accomplished by 64 * synchronizing on some object that naturally encapsulates the list. 65 * 66 * If no such object exists, the list should be "wrapped" using the 67 * {@link Collections#synchronizedList Collections.synchronizedList} 68 * method. This is best done at creation time, to prevent accidental 69 * unsynchronized access to the list:<pre> 70 * List list = Collections.synchronizedList(new ArrayList(...));</pre> 71 * 72 * <p><a name="fail-fast"> 73 * The iterators returned by this class's {@link #iterator() iterator} and 74 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:</a> 75 * if the list is structurally modified at any time after the iterator is 76 * created, in any way except through the iterator's own 77 * {@link ListIterator#remove() remove} or 78 * {@link ListIterator#add(Object) add} methods, the iterator will throw a 79 * {@link ConcurrentModificationException}. Thus, in the face of 80 * concurrent modification, the iterator fails quickly and cleanly, rather 81 * than risking arbitrary, non-deterministic behavior at an undetermined 82 * time in the future. 83 * 84 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 85 * as it is, generally speaking, impossible to make any hard guarantees in the 86 * presence of unsynchronized concurrent modification. Fail-fast iterators 87 * throw {@code ConcurrentModificationException} on a best-effort basis. 88 * Therefore, it would be wrong to write a program that depended on this 89 * exception for its correctness: <i>the fail-fast behavior of iterators 90 * should be used only to detect bugs.</i> 91 * 92 * <p>This class is a member of the 93 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 94 * Java Collections Framework</a>. 95 * 96 * @author Josh Bloch 97 * @author Neal Gafter 98 * @see Collection 99 * @see List 100 * @see LinkedList 101 * @see Vector 102 * @since 1.2 103 */ 104 105public class ArrayList<E> extends AbstractList<E> 106 implements List<E>, RandomAccess, Cloneable, java.io.Serializable 107{ 108 private static final long serialVersionUID = 8683452581122892189L; 109 110 /** 111 * Default initial capacity. 112 */ 113 private static final int DEFAULT_CAPACITY = 10; 114 115 /** 116 * Shared empty array instance used for empty instances. 117 */ 118 private static final Object[] EMPTY_ELEMENTDATA = {}; 119 120 /** 121 * The array buffer into which the elements of the ArrayList are stored. 122 * The capacity of the ArrayList is the length of this array buffer. Any 123 * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to 124 * DEFAULT_CAPACITY when the first element is added. 125 * 126 * Package private to allow access from java.util.Collections. 127 */ 128 transient Object[] elementData; 129 130 /** 131 * The size of the ArrayList (the number of elements it contains). 132 * 133 * @serial 134 */ 135 private int size; 136 137 /** 138 * Constructs an empty list with the specified initial capacity. 139 * 140 * @param initialCapacity the initial capacity of the list 141 * @throws IllegalArgumentException if the specified initial capacity 142 * is negative 143 */ 144 public ArrayList(int initialCapacity) { 145 super(); 146 if (initialCapacity < 0) 147 throw new IllegalArgumentException("Illegal Capacity: "+ 148 initialCapacity); 149 this.elementData = new Object[initialCapacity]; 150 } 151 152 /** 153 * Constructs an empty list with an initial capacity of ten. 154 */ 155 public ArrayList() { 156 super(); 157 this.elementData = EMPTY_ELEMENTDATA; 158 } 159 160 /** 161 * Constructs a list containing the elements of the specified 162 * collection, in the order they are returned by the collection's 163 * iterator. 164 * 165 * @param c the collection whose elements are to be placed into this list 166 * @throws NullPointerException if the specified collection is null 167 */ 168 public ArrayList(Collection<? extends E> c) { 169 elementData = c.toArray(); 170 size = elementData.length; 171 // c.toArray might (incorrectly) not return Object[] (see 6260652) 172 if (elementData.getClass() != Object[].class) 173 elementData = Arrays.copyOf(elementData, size, Object[].class); 174 } 175 176 /** 177 * Trims the capacity of this <tt>ArrayList</tt> instance to be the 178 * list's current size. An application can use this operation to minimize 179 * the storage of an <tt>ArrayList</tt> instance. 180 */ 181 public void trimToSize() { 182 modCount++; 183 if (size < elementData.length) { 184 elementData = Arrays.copyOf(elementData, size); 185 } 186 } 187 188 /** 189 * Increases the capacity of this <tt>ArrayList</tt> instance, if 190 * necessary, to ensure that it can hold at least the number of elements 191 * specified by the minimum capacity argument. 192 * 193 * @param minCapacity the desired minimum capacity 194 */ 195 public void ensureCapacity(int minCapacity) { 196 int minExpand = (elementData != EMPTY_ELEMENTDATA) 197 // any size if real element table 198 ? 0 199 // larger than default for empty table. It's already supposed to be 200 // at default size. 201 : DEFAULT_CAPACITY; 202 203 if (minCapacity > minExpand) { 204 ensureExplicitCapacity(minCapacity); 205 } 206 } 207 208 private void ensureCapacityInternal(int minCapacity) { 209 if (elementData == EMPTY_ELEMENTDATA) { 210 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); 211 } 212 213 ensureExplicitCapacity(minCapacity); 214 } 215 216 private void ensureExplicitCapacity(int minCapacity) { 217 modCount++; 218 219 // overflow-conscious code 220 if (minCapacity - elementData.length > 0) 221 grow(minCapacity); 222 } 223 224 /** 225 * The maximum size of array to allocate. 226 * Some VMs reserve some header words in an array. 227 * Attempts to allocate larger arrays may result in 228 * OutOfMemoryError: Requested array size exceeds VM limit 229 */ 230 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; 231 232 /** 233 * Increases the capacity to ensure that it can hold at least the 234 * number of elements specified by the minimum capacity argument. 235 * 236 * @param minCapacity the desired minimum capacity 237 */ 238 private void grow(int minCapacity) { 239 // overflow-conscious code 240 int oldCapacity = elementData.length; 241 int newCapacity = oldCapacity + (oldCapacity >> 1); 242 if (newCapacity - minCapacity < 0) 243 newCapacity = minCapacity; 244 if (newCapacity - MAX_ARRAY_SIZE > 0) 245 newCapacity = hugeCapacity(minCapacity); 246 // minCapacity is usually close to size, so this is a win: 247 elementData = Arrays.copyOf(elementData, newCapacity); 248 } 249 250 private static int hugeCapacity(int minCapacity) { 251 if (minCapacity < 0) // overflow 252 throw new OutOfMemoryError(); 253 return (minCapacity > MAX_ARRAY_SIZE) ? 254 Integer.MAX_VALUE : 255 MAX_ARRAY_SIZE; 256 } 257 258 /** 259 * Returns the number of elements in this list. 260 * 261 * @return the number of elements in this list 262 */ 263 public int size() { 264 return size; 265 } 266 267 /** 268 * Returns <tt>true</tt> if this list contains no elements. 269 * 270 * @return <tt>true</tt> if this list contains no elements 271 */ 272 public boolean isEmpty() { 273 return size == 0; 274 } 275 276 /** 277 * Returns <tt>true</tt> if this list contains the specified element. 278 * More formally, returns <tt>true</tt> if and only if this list contains 279 * at least one element <tt>e</tt> such that 280 * <tt>(o==null ? e==null : o.equals(e))</tt>. 281 * 282 * @param o element whose presence in this list is to be tested 283 * @return <tt>true</tt> if this list contains the specified element 284 */ 285 public boolean contains(Object o) { 286 return indexOf(o) >= 0; 287 } 288 289 /** 290 * Returns the index of the first occurrence of the specified element 291 * in this list, or -1 if this list does not contain the element. 292 * More formally, returns the lowest index <tt>i</tt> such that 293 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 294 * or -1 if there is no such index. 295 */ 296 public int indexOf(Object o) { 297 if (o == null) { 298 for (int i = 0; i < size; i++) 299 if (elementData[i]==null) 300 return i; 301 } else { 302 for (int i = 0; i < size; i++) 303 if (o.equals(elementData[i])) 304 return i; 305 } 306 return -1; 307 } 308 309 /** 310 * Returns the index of the last occurrence of the specified element 311 * in this list, or -1 if this list does not contain the element. 312 * More formally, returns the highest index <tt>i</tt> such that 313 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 314 * or -1 if there is no such index. 315 */ 316 public int lastIndexOf(Object o) { 317 if (o == null) { 318 for (int i = size-1; i >= 0; i--) 319 if (elementData[i]==null) 320 return i; 321 } else { 322 for (int i = size-1; i >= 0; i--) 323 if (o.equals(elementData[i])) 324 return i; 325 } 326 return -1; 327 } 328 329 /** 330 * Returns a shallow copy of this <tt>ArrayList</tt> instance. (The 331 * elements themselves are not copied.) 332 * 333 * @return a clone of this <tt>ArrayList</tt> instance 334 */ 335 public Object clone() { 336 try { 337 ArrayList<?> v = (ArrayList<?>) super.clone(); 338 v.elementData = Arrays.copyOf(elementData, size); 339 v.modCount = 0; 340 return v; 341 } catch (CloneNotSupportedException e) { 342 // this shouldn't happen, since we are Cloneable 343 throw new InternalError(e); 344 } 345 } 346 347 /** 348 * Returns an array containing all of the elements in this list 349 * in proper sequence (from first to last element). 350 * 351 * <p>The returned array will be "safe" in that no references to it are 352 * maintained by this list. (In other words, this method must allocate 353 * a new array). The caller is thus free to modify the returned array. 354 * 355 * <p>This method acts as bridge between array-based and collection-based 356 * APIs. 357 * 358 * @return an array containing all of the elements in this list in 359 * proper sequence 360 */ 361 public Object[] toArray() { 362 return Arrays.copyOf(elementData, size); 363 } 364 365 /** 366 * Returns an array containing all of the elements in this list in proper 367 * sequence (from first to last element); the runtime type of the returned 368 * array is that of the specified array. If the list fits in the 369 * specified array, it is returned therein. Otherwise, a new array is 370 * allocated with the runtime type of the specified array and the size of 371 * this list. 372 * 373 * <p>If the list fits in the specified array with room to spare 374 * (i.e., the array has more elements than the list), the element in 375 * the array immediately following the end of the collection is set to 376 * <tt>null</tt>. (This is useful in determining the length of the 377 * list <i>only</i> if the caller knows that the list does not contain 378 * any null elements.) 379 * 380 * @param a the array into which the elements of the list are to 381 * be stored, if it is big enough; otherwise, a new array of the 382 * same runtime type is allocated for this purpose. 383 * @return an array containing the elements of the list 384 * @throws ArrayStoreException if the runtime type of the specified array 385 * is not a supertype of the runtime type of every element in 386 * this list 387 * @throws NullPointerException if the specified array is null 388 */ 389 @SuppressWarnings("unchecked") 390 public <T> T[] toArray(T[] a) { 391 if (a.length < size) 392 // Make a new array of a's runtime type, but my contents: 393 return (T[]) Arrays.copyOf(elementData, size, a.getClass()); 394 System.arraycopy(elementData, 0, a, 0, size); 395 if (a.length > size) 396 a[size] = null; 397 return a; 398 } 399 400 /** 401 * Returns the element at the specified position in this list. 402 * 403 * @param index index of the element to return 404 * @return the element at the specified position in this list 405 * @throws IndexOutOfBoundsException {@inheritDoc} 406 */ 407 public E get(int index) { 408 if (index >= size) 409 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 410 411 return (E) elementData[index]; 412 } 413 414 /** 415 * Replaces the element at the specified position in this list with 416 * the specified element. 417 * 418 * @param index index of the element to replace 419 * @param element element to be stored at the specified position 420 * @return the element previously at the specified position 421 * @throws IndexOutOfBoundsException {@inheritDoc} 422 */ 423 public E set(int index, E element) { 424 if (index >= size) 425 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 426 427 E oldValue = (E) elementData[index]; 428 elementData[index] = element; 429 return oldValue; 430 } 431 432 /** 433 * Appends the specified element to the end of this list. 434 * 435 * @param e element to be appended to this list 436 * @return <tt>true</tt> (as specified by {@link Collection#add}) 437 */ 438 public boolean add(E e) { 439 ensureCapacityInternal(size + 1); // Increments modCount!! 440 elementData[size++] = e; 441 return true; 442 } 443 444 /** 445 * Inserts the specified element at the specified position in this 446 * list. Shifts the element currently at that position (if any) and 447 * any subsequent elements to the right (adds one to their indices). 448 * 449 * @param index index at which the specified element is to be inserted 450 * @param element element to be inserted 451 * @throws IndexOutOfBoundsException {@inheritDoc} 452 */ 453 public void add(int index, E element) { 454 if (index > size || index < 0) 455 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 456 457 ensureCapacityInternal(size + 1); // Increments modCount!! 458 System.arraycopy(elementData, index, elementData, index + 1, 459 size - index); 460 elementData[index] = element; 461 size++; 462 } 463 464 /** 465 * Removes the element at the specified position in this list. 466 * Shifts any subsequent elements to the left (subtracts one from their 467 * indices). 468 * 469 * @param index the index of the element to be removed 470 * @return the element that was removed from the list 471 * @throws IndexOutOfBoundsException {@inheritDoc} 472 */ 473 public E remove(int index) { 474 if (index >= size) 475 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 476 477 modCount++; 478 E oldValue = (E) elementData[index]; 479 480 int numMoved = size - index - 1; 481 if (numMoved > 0) 482 System.arraycopy(elementData, index+1, elementData, index, 483 numMoved); 484 elementData[--size] = null; // clear to let GC do its work 485 486 return oldValue; 487 } 488 489 /** 490 * Removes the first occurrence of the specified element from this list, 491 * if it is present. If the list does not contain the element, it is 492 * unchanged. More formally, removes the element with the lowest index 493 * <tt>i</tt> such that 494 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> 495 * (if such an element exists). Returns <tt>true</tt> if this list 496 * contained the specified element (or equivalently, if this list 497 * changed as a result of the call). 498 * 499 * @param o element to be removed from this list, if present 500 * @return <tt>true</tt> if this list contained the specified element 501 */ 502 public boolean remove(Object o) { 503 if (o == null) { 504 for (int index = 0; index < size; index++) 505 if (elementData[index] == null) { 506 fastRemove(index); 507 return true; 508 } 509 } else { 510 for (int index = 0; index < size; index++) 511 if (o.equals(elementData[index])) { 512 fastRemove(index); 513 return true; 514 } 515 } 516 return false; 517 } 518 519 /* 520 * Private remove method that skips bounds checking and does not 521 * return the value removed. 522 */ 523 private void fastRemove(int index) { 524 modCount++; 525 int numMoved = size - index - 1; 526 if (numMoved > 0) 527 System.arraycopy(elementData, index+1, elementData, index, 528 numMoved); 529 elementData[--size] = null; // clear to let GC do its work 530 } 531 532 /** 533 * Removes all of the elements from this list. The list will 534 * be empty after this call returns. 535 */ 536 public void clear() { 537 modCount++; 538 539 // clear to let GC do its work 540 for (int i = 0; i < size; i++) 541 elementData[i] = null; 542 543 size = 0; 544 } 545 546 /** 547 * Appends all of the elements in the specified collection to the end of 548 * this list, in the order that they are returned by the 549 * specified collection's Iterator. The behavior of this operation is 550 * undefined if the specified collection is modified while the operation 551 * is in progress. (This implies that the behavior of this call is 552 * undefined if the specified collection is this list, and this 553 * list is nonempty.) 554 * 555 * @param c collection containing elements to be added to this list 556 * @return <tt>true</tt> if this list changed as a result of the call 557 * @throws NullPointerException if the specified collection is null 558 */ 559 public boolean addAll(Collection<? extends E> c) { 560 Object[] a = c.toArray(); 561 int numNew = a.length; 562 ensureCapacityInternal(size + numNew); // Increments modCount 563 System.arraycopy(a, 0, elementData, size, numNew); 564 size += numNew; 565 return numNew != 0; 566 } 567 568 /** 569 * Inserts all of the elements in the specified collection into this 570 * list, starting at the specified position. Shifts the element 571 * currently at that position (if any) and any subsequent elements to 572 * the right (increases their indices). The new elements will appear 573 * in the list in the order that they are returned by the 574 * specified collection's iterator. 575 * 576 * @param index index at which to insert the first element from the 577 * specified collection 578 * @param c collection containing elements to be added to this list 579 * @return <tt>true</tt> if this list changed as a result of the call 580 * @throws IndexOutOfBoundsException {@inheritDoc} 581 * @throws NullPointerException if the specified collection is null 582 */ 583 public boolean addAll(int index, Collection<? extends E> c) { 584 if (index > size || index < 0) 585 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 586 587 Object[] a = c.toArray(); 588 int numNew = a.length; 589 ensureCapacityInternal(size + numNew); // Increments modCount 590 591 int numMoved = size - index; 592 if (numMoved > 0) 593 System.arraycopy(elementData, index, elementData, index + numNew, 594 numMoved); 595 596 System.arraycopy(a, 0, elementData, index, numNew); 597 size += numNew; 598 return numNew != 0; 599 } 600 601 /** 602 * Removes from this list all of the elements whose index is between 603 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. 604 * Shifts any succeeding elements to the left (reduces their index). 605 * This call shortens the list by {@code (toIndex - fromIndex)} elements. 606 * (If {@code toIndex==fromIndex}, this operation has no effect.) 607 * 608 * @throws IndexOutOfBoundsException if {@code fromIndex} or 609 * {@code toIndex} is out of range 610 * ({@code fromIndex < 0 || 611 * fromIndex >= size() || 612 * toIndex > size() || 613 * toIndex < fromIndex}) 614 */ 615 protected void removeRange(int fromIndex, int toIndex) { 616 // Android-changed : Throw an IOOBE if toIndex < fromIndex as documented. 617 // All the other cases (negative indices, or indices greater than the size 618 // will be thrown by System#arrayCopy. 619 if (toIndex < fromIndex) { 620 throw new IndexOutOfBoundsException("toIndex < fromIndex"); 621 } 622 623 modCount++; 624 int numMoved = size - toIndex; 625 System.arraycopy(elementData, toIndex, elementData, fromIndex, 626 numMoved); 627 628 // clear to let GC do its work 629 int newSize = size - (toIndex-fromIndex); 630 for (int i = newSize; i < size; i++) { 631 elementData[i] = null; 632 } 633 size = newSize; 634 } 635 636 /** 637 * Constructs an IndexOutOfBoundsException detail message. 638 * Of the many possible refactorings of the error handling code, 639 * this "outlining" performs best with both server and client VMs. 640 */ 641 private String outOfBoundsMsg(int index) { 642 return "Index: "+index+", Size: "+size; 643 } 644 645 /** 646 * Removes from this list all of its elements that are contained in the 647 * specified collection. 648 * 649 * @param c collection containing elements to be removed from this list 650 * @return {@code true} if this list changed as a result of the call 651 * @throws ClassCastException if the class of an element of this list 652 * is incompatible with the specified collection 653 * (<a href="Collection.html#optional-restrictions">optional</a>) 654 * @throws NullPointerException if this list contains a null element and the 655 * specified collection does not permit null elements 656 * (<a href="Collection.html#optional-restrictions">optional</a>), 657 * or if the specified collection is null 658 * @see Collection#contains(Object) 659 */ 660 public boolean removeAll(Collection<?> c) { 661 return batchRemove(c, false); 662 } 663 664 /** 665 * Retains only the elements in this list that are contained in the 666 * specified collection. In other words, removes from this list all 667 * of its elements that are not contained in the specified collection. 668 * 669 * @param c collection containing elements to be retained in this list 670 * @return {@code true} if this list changed as a result of the call 671 * @throws ClassCastException if the class of an element of this list 672 * is incompatible with the specified collection 673 * (<a href="Collection.html#optional-restrictions">optional</a>) 674 * @throws NullPointerException if this list contains a null element and the 675 * specified collection does not permit null elements 676 * (<a href="Collection.html#optional-restrictions">optional</a>), 677 * or if the specified collection is null 678 * @see Collection#contains(Object) 679 */ 680 public boolean retainAll(Collection<?> c) { 681 return batchRemove(c, true); 682 } 683 684 private boolean batchRemove(Collection<?> c, boolean complement) { 685 final Object[] elementData = this.elementData; 686 int r = 0, w = 0; 687 boolean modified = false; 688 try { 689 for (; r < size; r++) 690 if (c.contains(elementData[r]) == complement) 691 elementData[w++] = elementData[r]; 692 } finally { 693 // Preserve behavioral compatibility with AbstractCollection, 694 // even if c.contains() throws. 695 if (r != size) { 696 System.arraycopy(elementData, r, 697 elementData, w, 698 size - r); 699 w += size - r; 700 } 701 if (w != size) { 702 // clear to let GC do its work 703 for (int i = w; i < size; i++) 704 elementData[i] = null; 705 modCount += size - w; 706 size = w; 707 modified = true; 708 } 709 } 710 return modified; 711 } 712 713 /** 714 * Save the state of the <tt>ArrayList</tt> instance to a stream (that 715 * is, serialize it). 716 * 717 * @serialData The length of the array backing the <tt>ArrayList</tt> 718 * instance is emitted (int), followed by all of its elements 719 * (each an <tt>Object</tt>) in the proper order. 720 */ 721 private void writeObject(java.io.ObjectOutputStream s) 722 throws java.io.IOException{ 723 // Write out element count, and any hidden stuff 724 int expectedModCount = modCount; 725 s.defaultWriteObject(); 726 727 // Write out size as capacity for behavioural compatibility with clone() 728 s.writeInt(size); 729 730 // Write out all elements in the proper order. 731 for (int i=0; i<size; i++) { 732 s.writeObject(elementData[i]); 733 } 734 735 if (modCount != expectedModCount) { 736 throw new ConcurrentModificationException(); 737 } 738 } 739 740 /** 741 * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is, 742 * deserialize it). 743 */ 744 private void readObject(java.io.ObjectInputStream s) 745 throws java.io.IOException, ClassNotFoundException { 746 elementData = EMPTY_ELEMENTDATA; 747 748 // Read in size, and any hidden stuff 749 s.defaultReadObject(); 750 751 // Read in capacity 752 s.readInt(); // ignored 753 754 if (size > 0) { 755 // be like clone(), allocate array based upon size not capacity 756 ensureCapacityInternal(size); 757 758 Object[] a = elementData; 759 // Read in all elements in the proper order. 760 for (int i=0; i<size; i++) { 761 a[i] = s.readObject(); 762 } 763 } 764 } 765 766 /** 767 * Returns a list iterator over the elements in this list (in proper 768 * sequence), starting at the specified position in the list. 769 * The specified index indicates the first element that would be 770 * returned by an initial call to {@link ListIterator#next next}. 771 * An initial call to {@link ListIterator#previous previous} would 772 * return the element with the specified index minus one. 773 * 774 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>. 775 * 776 * @throws IndexOutOfBoundsException {@inheritDoc} 777 */ 778 public ListIterator<E> listIterator(int index) { 779 if (index < 0 || index > size) 780 throw new IndexOutOfBoundsException("Index: "+index); 781 return new ListItr(index); 782 } 783 784 /** 785 * Returns a list iterator over the elements in this list (in proper 786 * sequence). 787 * 788 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>. 789 * 790 * @see #listIterator(int) 791 */ 792 public ListIterator<E> listIterator() { 793 return new ListItr(0); 794 } 795 796 /** 797 * Returns an iterator over the elements in this list in proper sequence. 798 * 799 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>. 800 * 801 * @return an iterator over the elements in this list in proper sequence 802 */ 803 public Iterator<E> iterator() { 804 return new Itr(); 805 } 806 807 /** 808 * An optimized version of AbstractList.Itr 809 */ 810 private class Itr implements Iterator<E> { 811 // The "limit" of this iterator. This is the size of the list at the time the 812 // iterator was created. Adding & removing elements will invalidate the iteration 813 // anyway (and cause next() to throw) so saving this value will guarantee that the 814 // value of hasNext() remains stable and won't flap between true and false when elements 815 // are added and removed from the list. 816 protected int limit = ArrayList.this.size; 817 818 int cursor; // index of next element to return 819 int lastRet = -1; // index of last element returned; -1 if no such 820 int expectedModCount = modCount; 821 822 public boolean hasNext() { 823 return cursor < limit; 824 } 825 826 @SuppressWarnings("unchecked") 827 public E next() { 828 if (modCount != expectedModCount) 829 throw new ConcurrentModificationException(); 830 int i = cursor; 831 if (i >= limit) 832 throw new NoSuchElementException(); 833 Object[] elementData = ArrayList.this.elementData; 834 if (i >= elementData.length) 835 throw new ConcurrentModificationException(); 836 cursor = i + 1; 837 return (E) elementData[lastRet = i]; 838 } 839 840 public void remove() { 841 if (lastRet < 0) 842 throw new IllegalStateException(); 843 if (modCount != expectedModCount) 844 throw new ConcurrentModificationException(); 845 846 try { 847 ArrayList.this.remove(lastRet); 848 cursor = lastRet; 849 lastRet = -1; 850 expectedModCount = modCount; 851 limit--; 852 } catch (IndexOutOfBoundsException ex) { 853 throw new ConcurrentModificationException(); 854 } 855 } 856 857 @Override 858 @SuppressWarnings("unchecked") 859 public void forEachRemaining(Consumer<? super E> consumer) { 860 Objects.requireNonNull(consumer); 861 final int size = ArrayList.this.size; 862 int i = cursor; 863 if (i >= size) { 864 return; 865 } 866 final Object[] elementData = ArrayList.this.elementData; 867 if (i >= elementData.length) { 868 throw new ConcurrentModificationException(); 869 } 870 while (i != size && modCount == expectedModCount) { 871 consumer.accept((E) elementData[i++]); 872 } 873 // update once at end of iteration to reduce heap write traffic 874 cursor = i; 875 lastRet = i - 1; 876 877 if (modCount != expectedModCount) 878 throw new ConcurrentModificationException(); 879 } 880 } 881 882 /** 883 * An optimized version of AbstractList.ListItr 884 */ 885 private class ListItr extends Itr implements ListIterator<E> { 886 ListItr(int index) { 887 super(); 888 cursor = index; 889 } 890 891 public boolean hasPrevious() { 892 return cursor != 0; 893 } 894 895 public int nextIndex() { 896 return cursor; 897 } 898 899 public int previousIndex() { 900 return cursor - 1; 901 } 902 903 @SuppressWarnings("unchecked") 904 public E previous() { 905 if (modCount != expectedModCount) 906 throw new ConcurrentModificationException(); 907 int i = cursor - 1; 908 if (i < 0) 909 throw new NoSuchElementException(); 910 Object[] elementData = ArrayList.this.elementData; 911 if (i >= elementData.length) 912 throw new ConcurrentModificationException(); 913 cursor = i; 914 return (E) elementData[lastRet = i]; 915 } 916 917 public void set(E e) { 918 if (lastRet < 0) 919 throw new IllegalStateException(); 920 if (modCount != expectedModCount) 921 throw new ConcurrentModificationException(); 922 923 try { 924 ArrayList.this.set(lastRet, e); 925 } catch (IndexOutOfBoundsException ex) { 926 throw new ConcurrentModificationException(); 927 } 928 } 929 930 public void add(E e) { 931 if (modCount != expectedModCount) 932 throw new ConcurrentModificationException(); 933 934 try { 935 int i = cursor; 936 ArrayList.this.add(i, e); 937 cursor = i + 1; 938 lastRet = -1; 939 expectedModCount = modCount; 940 limit++; 941 } catch (IndexOutOfBoundsException ex) { 942 throw new ConcurrentModificationException(); 943 } 944 } 945 } 946 947 /** 948 * Returns a view of the portion of this list between the specified 949 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If 950 * {@code fromIndex} and {@code toIndex} are equal, the returned list is 951 * empty.) The returned list is backed by this list, so non-structural 952 * changes in the returned list are reflected in this list, and vice-versa. 953 * The returned list supports all of the optional list operations. 954 * 955 * <p>This method eliminates the need for explicit range operations (of 956 * the sort that commonly exist for arrays). Any operation that expects 957 * a list can be used as a range operation by passing a subList view 958 * instead of a whole list. For example, the following idiom 959 * removes a range of elements from a list: 960 * <pre> 961 * list.subList(from, to).clear(); 962 * </pre> 963 * Similar idioms may be constructed for {@link #indexOf(Object)} and 964 * {@link #lastIndexOf(Object)}, and all of the algorithms in the 965 * {@link Collections} class can be applied to a subList. 966 * 967 * <p>The semantics of the list returned by this method become undefined if 968 * the backing list (i.e., this list) is <i>structurally modified</i> in 969 * any way other than via the returned list. (Structural modifications are 970 * those that change the size of this list, or otherwise perturb it in such 971 * a fashion that iterations in progress may yield incorrect results.) 972 * 973 * @throws IndexOutOfBoundsException {@inheritDoc} 974 * @throws IllegalArgumentException {@inheritDoc} 975 */ 976 public List<E> subList(int fromIndex, int toIndex) { 977 subListRangeCheck(fromIndex, toIndex, size); 978 return new SubList(this, 0, fromIndex, toIndex); 979 } 980 981 static void subListRangeCheck(int fromIndex, int toIndex, int size) { 982 if (fromIndex < 0) 983 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 984 if (toIndex > size) 985 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 986 if (fromIndex > toIndex) 987 throw new IllegalArgumentException("fromIndex(" + fromIndex + 988 ") > toIndex(" + toIndex + ")"); 989 } 990 991 private class SubList extends AbstractList<E> implements RandomAccess { 992 private final AbstractList<E> parent; 993 private final int parentOffset; 994 private final int offset; 995 int size; 996 997 SubList(AbstractList<E> parent, 998 int offset, int fromIndex, int toIndex) { 999 this.parent = parent; 1000 this.parentOffset = fromIndex; 1001 this.offset = offset + fromIndex; 1002 this.size = toIndex - fromIndex; 1003 this.modCount = ArrayList.this.modCount; 1004 } 1005 1006 public E set(int index, E e) { 1007 if (index < 0 || index >= this.size) 1008 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1009 if (ArrayList.this.modCount != this.modCount) 1010 throw new ConcurrentModificationException(); 1011 E oldValue = (E) ArrayList.this.elementData[offset + index]; 1012 ArrayList.this.elementData[offset + index] = e; 1013 return oldValue; 1014 } 1015 1016 public E get(int index) { 1017 if (index < 0 || index >= this.size) 1018 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1019 if (ArrayList.this.modCount != this.modCount) 1020 throw new ConcurrentModificationException(); 1021 return (E) ArrayList.this.elementData[offset + index]; 1022 } 1023 1024 public int size() { 1025 if (ArrayList.this.modCount != this.modCount) 1026 throw new ConcurrentModificationException(); 1027 return this.size; 1028 } 1029 1030 public void add(int index, E e) { 1031 if (index < 0 || index > this.size) 1032 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1033 if (ArrayList.this.modCount != this.modCount) 1034 throw new ConcurrentModificationException(); 1035 parent.add(parentOffset + index, e); 1036 this.modCount = parent.modCount; 1037 this.size++; 1038 } 1039 1040 public E remove(int index) { 1041 if (index < 0 || index >= this.size) 1042 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1043 if (ArrayList.this.modCount != this.modCount) 1044 throw new ConcurrentModificationException(); 1045 E result = parent.remove(parentOffset + index); 1046 this.modCount = parent.modCount; 1047 this.size--; 1048 return result; 1049 } 1050 1051 protected void removeRange(int fromIndex, int toIndex) { 1052 if (ArrayList.this.modCount != this.modCount) 1053 throw new ConcurrentModificationException(); 1054 parent.removeRange(parentOffset + fromIndex, 1055 parentOffset + toIndex); 1056 this.modCount = parent.modCount; 1057 this.size -= toIndex - fromIndex; 1058 } 1059 1060 public boolean addAll(Collection<? extends E> c) { 1061 return addAll(this.size, c); 1062 } 1063 1064 public boolean addAll(int index, Collection<? extends E> c) { 1065 if (index < 0 || index > this.size) 1066 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1067 int cSize = c.size(); 1068 if (cSize==0) 1069 return false; 1070 1071 if (ArrayList.this.modCount != this.modCount) 1072 throw new ConcurrentModificationException(); 1073 parent.addAll(parentOffset + index, c); 1074 this.modCount = parent.modCount; 1075 this.size += cSize; 1076 return true; 1077 } 1078 1079 public Iterator<E> iterator() { 1080 return listIterator(); 1081 } 1082 1083 public ListIterator<E> listIterator(final int index) { 1084 if (ArrayList.this.modCount != this.modCount) 1085 throw new ConcurrentModificationException(); 1086 if (index < 0 || index > this.size) 1087 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 1088 final int offset = this.offset; 1089 1090 return new ListIterator<E>() { 1091 int cursor = index; 1092 int lastRet = -1; 1093 int expectedModCount = ArrayList.this.modCount; 1094 1095 public boolean hasNext() { 1096 return cursor != SubList.this.size; 1097 } 1098 1099 @SuppressWarnings("unchecked") 1100 public E next() { 1101 if (expectedModCount != ArrayList.this.modCount) 1102 throw new ConcurrentModificationException(); 1103 int i = cursor; 1104 if (i >= SubList.this.size) 1105 throw new NoSuchElementException(); 1106 Object[] elementData = ArrayList.this.elementData; 1107 if (offset + i >= elementData.length) 1108 throw new ConcurrentModificationException(); 1109 cursor = i + 1; 1110 return (E) elementData[offset + (lastRet = i)]; 1111 } 1112 1113 public boolean hasPrevious() { 1114 return cursor != 0; 1115 } 1116 1117 @SuppressWarnings("unchecked") 1118 public E previous() { 1119 if (expectedModCount != ArrayList.this.modCount) 1120 throw new ConcurrentModificationException(); 1121 int i = cursor - 1; 1122 if (i < 0) 1123 throw new NoSuchElementException(); 1124 Object[] elementData = ArrayList.this.elementData; 1125 if (offset + i >= elementData.length) 1126 throw new ConcurrentModificationException(); 1127 cursor = i; 1128 return (E) elementData[offset + (lastRet = i)]; 1129 } 1130 1131 @SuppressWarnings("unchecked") 1132 public void forEachRemaining(Consumer<? super E> consumer) { 1133 Objects.requireNonNull(consumer); 1134 final int size = SubList.this.size; 1135 int i = cursor; 1136 if (i >= size) { 1137 return; 1138 } 1139 final Object[] elementData = ArrayList.this.elementData; 1140 if (offset + i >= elementData.length) { 1141 throw new ConcurrentModificationException(); 1142 } 1143 while (i != size && modCount == expectedModCount) { 1144 consumer.accept((E) elementData[offset + (i++)]); 1145 } 1146 // update once at end of iteration to reduce heap write traffic 1147 lastRet = cursor = i; 1148 if (expectedModCount != ArrayList.this.modCount) 1149 throw new ConcurrentModificationException(); 1150 } 1151 1152 public int nextIndex() { 1153 return cursor; 1154 } 1155 1156 public int previousIndex() { 1157 return cursor - 1; 1158 } 1159 1160 public void remove() { 1161 if (lastRet < 0) 1162 throw new IllegalStateException(); 1163 if (expectedModCount != ArrayList.this.modCount) 1164 throw new ConcurrentModificationException(); 1165 1166 try { 1167 SubList.this.remove(lastRet); 1168 cursor = lastRet; 1169 lastRet = -1; 1170 expectedModCount = ArrayList.this.modCount; 1171 } catch (IndexOutOfBoundsException ex) { 1172 throw new ConcurrentModificationException(); 1173 } 1174 } 1175 1176 public void set(E e) { 1177 if (lastRet < 0) 1178 throw new IllegalStateException(); 1179 if (expectedModCount != ArrayList.this.modCount) 1180 throw new ConcurrentModificationException(); 1181 1182 try { 1183 ArrayList.this.set(offset + lastRet, e); 1184 } catch (IndexOutOfBoundsException ex) { 1185 throw new ConcurrentModificationException(); 1186 } 1187 } 1188 1189 public void add(E e) { 1190 if (expectedModCount != ArrayList.this.modCount) 1191 throw new ConcurrentModificationException(); 1192 1193 try { 1194 int i = cursor; 1195 SubList.this.add(i, e); 1196 cursor = i + 1; 1197 lastRet = -1; 1198 expectedModCount = ArrayList.this.modCount; 1199 } catch (IndexOutOfBoundsException ex) { 1200 throw new ConcurrentModificationException(); 1201 } 1202 } 1203 }; 1204 } 1205 1206 public List<E> subList(int fromIndex, int toIndex) { 1207 subListRangeCheck(fromIndex, toIndex, size); 1208 return new SubList(this, offset, fromIndex, toIndex); 1209 } 1210 1211 private String outOfBoundsMsg(int index) { 1212 return "Index: "+index+", Size: "+this.size; 1213 } 1214 } 1215 1216 @Override 1217 public void forEach(Consumer<? super E> action) { 1218 Objects.requireNonNull(action); 1219 final int expectedModCount = modCount; 1220 @SuppressWarnings("unchecked") 1221 final E[] elementData = (E[]) this.elementData; 1222 final int size = this.size; 1223 for (int i=0; modCount == expectedModCount && i < size; i++) { 1224 action.accept(elementData[i]); 1225 } 1226 // Note 1227 // Iterator will not throw a CME if we add something while iterating over the *last* element 1228 // forEach will throw a CME in this case. 1229 if (modCount != expectedModCount) { 1230 throw new ConcurrentModificationException(); 1231 } 1232 } 1233 1234 /** 1235 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> 1236 * and <em>fail-fast</em> {@link Spliterator} over the elements in this 1237 * list. 1238 * 1239 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, 1240 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}. 1241 * Overriding implementations should document the reporting of additional 1242 * characteristic values. 1243 * 1244 * @return a {@code Spliterator} over the elements in this list 1245 * @since 1.8 1246 */ 1247 @Override 1248 public Spliterator<E> spliterator() { 1249 return new ArrayListSpliterator<>(this, 0, -1, 0); 1250 } 1251 1252 /** Index-based split-by-two, lazily initialized Spliterator */ 1253 static final class ArrayListSpliterator<E> implements Spliterator<E> { 1254 1255 /* 1256 * If ArrayLists were immutable, or structurally immutable (no 1257 * adds, removes, etc), we could implement their spliterators 1258 * with Arrays.spliterator. Instead we detect as much 1259 * interference during traversal as practical without 1260 * sacrificing much performance. We rely primarily on 1261 * modCounts. These are not guaranteed to detect concurrency 1262 * violations, and are sometimes overly conservative about 1263 * within-thread interference, but detect enough problems to 1264 * be worthwhile in practice. To carry this out, we (1) lazily 1265 * initialize fence and expectedModCount until the latest 1266 * point that we need to commit to the state we are checking 1267 * against; thus improving precision. (This doesn't apply to 1268 * SubLists, that create spliterators with current non-lazy 1269 * values). (2) We perform only a single 1270 * ConcurrentModificationException check at the end of forEach 1271 * (the most performance-sensitive method). When using forEach 1272 * (as opposed to iterators), we can normally only detect 1273 * interference after actions, not before. Further 1274 * CME-triggering checks apply to all other possible 1275 * violations of assumptions for example null or too-small 1276 * elementData array given its size(), that could only have 1277 * occurred due to interference. This allows the inner loop 1278 * of forEach to run without any further checks, and 1279 * simplifies lambda-resolution. While this does entail a 1280 * number of checks, note that in the common case of 1281 * list.stream().forEach(a), no checks or other computation 1282 * occur anywhere other than inside forEach itself. The other 1283 * less-often-used methods cannot take advantage of most of 1284 * these streamlinings. 1285 */ 1286 1287 private final ArrayList<E> list; 1288 private int index; // current index, modified on advance/split 1289 private int fence; // -1 until used; then one past last index 1290 private int expectedModCount; // initialized when fence set 1291 1292 /** Create new spliterator covering the given range */ 1293 ArrayListSpliterator(ArrayList<E> list, int origin, int fence, 1294 int expectedModCount) { 1295 this.list = list; // OK if null unless traversed 1296 this.index = origin; 1297 this.fence = fence; 1298 this.expectedModCount = expectedModCount; 1299 } 1300 1301 private int getFence() { // initialize fence to size on first use 1302 int hi; // (a specialized variant appears in method forEach) 1303 ArrayList<E> lst; 1304 if ((hi = fence) < 0) { 1305 if ((lst = list) == null) 1306 hi = fence = 0; 1307 else { 1308 expectedModCount = lst.modCount; 1309 hi = fence = lst.size; 1310 } 1311 } 1312 return hi; 1313 } 1314 1315 public ArrayListSpliterator<E> trySplit() { 1316 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1317 return (lo >= mid) ? null : // divide range in half unless too small 1318 new ArrayListSpliterator<E>(list, lo, index = mid, 1319 expectedModCount); 1320 } 1321 1322 public boolean tryAdvance(Consumer<? super E> action) { 1323 if (action == null) 1324 throw new NullPointerException(); 1325 int hi = getFence(), i = index; 1326 if (i < hi) { 1327 index = i + 1; 1328 @SuppressWarnings("unchecked") E e = (E)list.elementData[i]; 1329 action.accept(e); 1330 if (list.modCount != expectedModCount) 1331 throw new ConcurrentModificationException(); 1332 return true; 1333 } 1334 return false; 1335 } 1336 1337 public void forEachRemaining(Consumer<? super E> action) { 1338 int i, hi, mc; // hoist accesses and checks from loop 1339 ArrayList<E> lst; Object[] a; 1340 if (action == null) 1341 throw new NullPointerException(); 1342 if ((lst = list) != null && (a = lst.elementData) != null) { 1343 if ((hi = fence) < 0) { 1344 mc = lst.modCount; 1345 hi = lst.size; 1346 } 1347 else 1348 mc = expectedModCount; 1349 if ((i = index) >= 0 && (index = hi) <= a.length) { 1350 for (; i < hi; ++i) { 1351 @SuppressWarnings("unchecked") E e = (E) a[i]; 1352 action.accept(e); 1353 } 1354 if (lst.modCount == mc) 1355 return; 1356 } 1357 } 1358 throw new ConcurrentModificationException(); 1359 } 1360 1361 public long estimateSize() { 1362 return (long) (getFence() - index); 1363 } 1364 1365 public int characteristics() { 1366 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED; 1367 } 1368 } 1369} 1370