ArrayList.java |
1 /* 2 * %W% %E% 3 * 4 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved. 5 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. 6 */ 7 8 package java.util; 9 10 /** 11 * Resizable-array implementation of the <tt>List</tt> interface. Implements 12 * all optional list operations, and permits all elements, including 13 * <tt>null</tt>. In addition to implementing the <tt>List</tt> interface, 14 * this class provides methods to manipulate the size of the array that is 15 * used internally to store the list. (This class is roughly equivalent to 16 * <tt>Vector</tt>, except that it is unsynchronized.)<p> 17 * 18 * The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>, 19 * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant 20 * time. The <tt>add</tt> operation runs in <i>amortized constant time</i>, 21 * that is, adding n elements requires O(n) time. All of the other operations 22 * run in linear time (roughly speaking). The constant factor is low compared 23 * to that for the <tt>LinkedList</tt> implementation.<p> 24 * 25 * Each <tt>ArrayList</tt> instance has a <i>capacity</i>. The capacity is 26 * the size of the array used to store the elements in the list. It is always 27 * at least as large as the list size. As elements are added to an ArrayList, 28 * its capacity grows automatically. The details of the growth policy are not 29 * specified beyond the fact that adding an element has constant amortized 30 * time cost.<p> 31 * 32 * An application can increase the capacity of an <tt>ArrayList</tt> instance 33 * before adding a large number of elements using the <tt>ensureCapacity</tt> 34 * operation. This may reduce the amount of incremental reallocation. 35 * 36 * <p><strong>Note that this implementation is not synchronized.</strong> 37 * If multiple threads access an <tt>ArrayList</tt> instance concurrently, 38 * and at least one of the threads modifies the list structurally, it 39 * <i>must</i> be synchronized externally. (A structural modification is 40 * any operation that adds or deletes one or more elements, or explicitly 41 * resizes the backing array; merely setting the value of an element is not 42 * a structural modification.) This is typically accomplished by 43 * synchronizing on some object that naturally encapsulates the list. 44 * 45 * If no such object exists, the list should be "wrapped" using the 46 * {@link Collections#synchronizedList Collections.synchronizedList} 47 * method. This is best done at creation time, to prevent accidental 48 * unsynchronized access to the list:<pre> 49 * List list = Collections.synchronizedList(new ArrayList(...));</pre> 50 * 51 * <p>The iterators returned by this class's <tt>iterator</tt> and 52 * <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is 53 * structurally modified at any time after the iterator is created, in any way 54 * except through the iterator's own <tt>remove</tt> or <tt>add</tt> methods, 55 * the iterator will throw a {@link ConcurrentModificationException}. Thus, in 56 * the face of concurrent modification, the iterator fails quickly and cleanly, 57 * rather than risking arbitrary, non-deterministic behavior at an undetermined 58 * time in the future.<p> 59 * 60 * Note that the fail-fast behavior of an iterator cannot be guaranteed 61 * as it is, generally speaking, impossible to make any hard guarantees in the 62 * presence of unsynchronized concurrent modification. Fail-fast iterators 63 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 64 * Therefore, it would be wrong to write a program that depended on this 65 * exception for its correctness: <i>the fail-fast behavior of iterators 66 * should be used only to detect bugs.</i><p> 67 * 68 * This class is a member of the 69 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 70 * Java Collections Framework</a>. 71 * 72 * @author Josh Bloch 73 * @author Neal Gafter 74 * @version %I%, %G% 75 * @see Collection 76 * @see List 77 * @see LinkedList 78 * @see Vector 79 * @since 1.2 80 */ 81 82 public class ArrayList<E> extends AbstractList<E> 83 implements List<E>, RandomAccess, Cloneable, java.io.Serializable 84 { 85 private static final long serialVersionUID = 8683452581122892189L; 86 87 /** 88 * The array buffer into which the elements of the ArrayList are stored. 89 * The capacity of the ArrayList is the length of this array buffer. 90 */ 91 private transient Object[] elementData; 92 93 /** 94 * The size of the ArrayList (the number of elements it contains). 95 * 96 * @serial 97 */ 98 private int size; 99 100 /** 101 * Constructs an empty list with the specified initial capacity. 102 * 103 * @param initialCapacity the initial capacity of the list 104 * @exception IllegalArgumentException if the specified initial capacity 105 * is negative 106 */ 107 public ArrayList(int initialCapacity) { 108 super(); 109 if (initialCapacity < 0) 110 throw new IllegalArgumentException("Illegal Capacity: "+ 111 initialCapacity); 112 this.elementData = new Object[initialCapacity]; 113 } 114 115 /** 116 * Constructs an empty list with an initial capacity of ten. 117 */ 118 public ArrayList() { 119 this(10); 120 } 121 122 /** 123 * Constructs a list containing the elements of the specified 124 * collection, in the order they are returned by the collection's 125 * iterator. 126 * 127 * @param c the collection whose elements are to be placed into this list 128 * @throws NullPointerException if the specified collection is null 129 */ 130 public ArrayList(Collection<? extends E> c) { 131 elementData = c.toArray(); 132 size = elementData.length; 133 // c.toArray might (incorrectly) not return Object[] (see 6260652) 134 if (elementData.getClass() != Object[].class) 135 elementData = Arrays.copyOf(elementData, size, Object[].class); 136 } 137 138 /** 139 * Trims the capacity of this <tt>ArrayList</tt> instance to be the 140 * list's current size. An application can use this operation to minimize 141 * the storage of an <tt>ArrayList</tt> instance. 142 */ 143 public void trimToSize() { 144 modCount++; 145 int oldCapacity = elementData.length; 146 if (size < oldCapacity) { 147 elementData = Arrays.copyOf(elementData, size); 148 } 149 } 150 151 /** 152 * Increases the capacity of this <tt>ArrayList</tt> instance, if 153 * necessary, to ensure that it can hold at least the number of elements 154 * specified by the minimum capacity argument. 155 * 156 * @param minCapacity the desired minimum capacity 157 */ 158 public void ensureCapacity(int minCapacity) { 159 modCount++; 160 int oldCapacity = elementData.length; 161 if (minCapacity > oldCapacity) { 162 Object oldData[] = elementData; 163 int newCapacity = (oldCapacity * 3)/2 + 1; 164 if (newCapacity < minCapacity) 165 newCapacity = minCapacity; 166 // minCapacity is usually close to size, so this is a win: 167 elementData = Arrays.copyOf(elementData, newCapacity); 168 } 169 } 170 171 /** 172 * Returns the number of elements in this list. 173 * 174 * @return the number of elements in this list 175 */ 176 public int size() { 177 return size; 178 } 179 180 /** 181 * Returns <tt>true</tt> if this list contains no elements. 182 * 183 * @return <tt>true</tt> if this list contains no elements 184 */ 185 public boolean isEmpty() { 186 return size == 0; 187 } 188 189 /** 190 * Returns <tt>true</tt> if this list contains the specified element. 191 * More formally, returns <tt>true</tt> if and only if this list contains 192 * at least one element <tt>e</tt> such that 193 * <tt>(o==null ? e==null : o.equals(e))</tt>. 194 * 195 * @param o element whose presence in this list is to be tested 196 * @return <tt>true</tt> if this list contains the specified element 197 */ 198 public boolean contains(Object o) { 199 return indexOf(o) >= 0; 200 } 201 202 /** 203 * Returns the index of the first occurrence of the specified element 204 * in this list, or -1 if this list does not contain the element. 205 * More formally, returns the lowest index <tt>i</tt> such that 206 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 207 * or -1 if there is no such index. 208 */ 209 public int indexOf(Object o) { 210 if (o == null) { 211 for (int i = 0; i < size; i++) 212 if (elementData[i]==null) 213 return i; 214 } else { 215 for (int i = 0; i < size; i++) 216 if (o.equals(elementData[i])) 217 return i; 218 } 219 return -1; 220 } 221 222 /** 223 * Returns the index of the last occurrence of the specified element 224 * in this list, or -1 if this list does not contain the element. 225 * More formally, returns the highest index <tt>i</tt> such that 226 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, 227 * or -1 if there is no such index. 228 */ 229 public int lastIndexOf(Object o) { 230 if (o == null) { 231 for (int i = size-1; i >= 0; i--) 232 if (elementData[i]==null) 233 return i; 234 } else { 235 for (int i = size-1; i >= 0; i--) 236 if (o.equals(elementData[i])) 237 return i; 238 } 239 return -1; 240 } 241 242 /** 243 * Returns a shallow copy of this <tt>ArrayList</tt> instance. (The 244 * elements themselves are not copied.) 245 * 246 * @return a clone of this <tt>ArrayList</tt> instance 247 */ 248 public Object clone() { 249 try { 250 ArrayList<E> v = (ArrayList<E>) super.clone(); 251 v.elementData = Arrays.copyOf(elementData, size); 252 v.modCount = 0; 253 return v; 254 } catch (CloneNotSupportedException e) { 255 // this shouldn't happen, since we are Cloneable 256 throw new InternalError(); 257 } 258 } 259 260 /** 261 * Returns an array containing all of the elements in this list 262 * in proper sequence (from first to last element). 263 * 264 * <p>The returned array will be "safe" in that no references to it are 265 * maintained by this list. (In other words, this method must allocate 266 * a new array). The caller is thus free to modify the returned array. 267 * 268 * <p>This method acts as bridge between array-based and collection-based 269 * APIs. 270 * 271 * @return an array containing all of the elements in this list in 272 * proper sequence 273 */ 274 public Object[] toArray() { 275 return Arrays.copyOf(elementData, size); 276 } 277 278 /** 279 * Returns an array containing all of the elements in this list in proper 280 * sequence (from first to last element); the runtime type of the returned 281 * array is that of the specified array. If the list fits in the 282 * specified array, it is returned therein. Otherwise, a new array is 283 * allocated with the runtime type of the specified array and the size of 284 * this list. 285 * 286 * <p>If the list fits in the specified array with room to spare 287 * (i.e., the array has more elements than the list), the element in 288 * the array immediately following the end of the collection is set to 289 * <tt>null</tt>. (This is useful in determining the length of the 290 * list <i>only</i> if the caller knows that the list does not contain 291 * any null elements.) 292 * 293 * @param a the array into which the elements of the list are to 294 * be stored, if it is big enough; otherwise, a new array of the 295 * same runtime type is allocated for this purpose. 296 * @return an array containing the elements of the list 297 * @throws ArrayStoreException if the runtime type of the specified array 298 * is not a supertype of the runtime type of every element in 299 * this list 300 * @throws NullPointerException if the specified array is null 301 */ 302 public <T> T[] toArray(T[] a) { 303 if (a.length < size) 304 // Make a new array of a's runtime type, but my contents: 305 return (T[]) Arrays.copyOf(elementData, size, a.getClass()); 306 System.arraycopy(elementData, 0, a, 0, size); 307 if (a.length > size) 308 a[size] = null; 309 return a; 310 } 311 312 // Positional Access Operations 313 314 /** 315 * Returns the element at the specified position in this list. 316 * 317 * @param index index of the element to return 318 * @return the element at the specified position in this list 319 * @throws IndexOutOfBoundsException {@inheritDoc} 320 */ 321 public E get(int index) { 322 RangeCheck(index); 323 324 return (E) elementData[index]; 325 } 326 327 /** 328 * Replaces the element at the specified position in this list with 329 * the specified element. 330 * 331 * @param index index of the element to replace 332 * @param element element to be stored at the specified position 333 * @return the element previously at the specified position 334 * @throws IndexOutOfBoundsException {@inheritDoc} 335 */ 336 public E set(int index, E element) { 337 RangeCheck(index); 338 339 E oldValue = (E) elementData[index]; 340 elementData[index] = element; 341 return oldValue; 342 } 343 344 /** 345 * Appends the specified element to the end of this list. 346 * 347 * @param e element to be appended to this list 348 * @return <tt>true</tt> (as specified by {@link Collection#add}) 349 */ 350 public boolean add(E e) { 351 ensureCapacity(size + 1); // Increments modCount!! 352 elementData[size++] = e; 353 return true; 354 } 355 356 /** 357 * Inserts the specified element at the specified position in this 358 * list. Shifts the element currently at that position (if any) and 359 * any subsequent elements to the right (adds one to their indices). 360 * 361 * @param index index at which the specified element is to be inserted 362 * @param element element to be inserted 363 * @throws IndexOutOfBoundsException {@inheritDoc} 364 */ 365 public void add(int index, E element) { 366 if (index > size || index < 0) 367 throw new IndexOutOfBoundsException( 368 "Index: "+index+", Size: "+size); 369 370 ensureCapacity(size+1); // Increments modCount!! 371 System.arraycopy(elementData, index, elementData, index + 1, 372 size - index); 373 elementData[index] = element; 374 size++; 375 } 376 377 /** 378 * Removes the element at the specified position in this list. 379 * Shifts any subsequent elements to the left (subtracts one from their 380 * indices). 381 * 382 * @param index the index of the element to be removed 383 * @return the element that was removed from the list 384 * @throws IndexOutOfBoundsException {@inheritDoc} 385 */ 386 public E remove(int index) { 387 RangeCheck(index); 388 389 modCount++; 390 E oldValue = (E) elementData[index]; 391 392 int numMoved = size - index - 1; 393 if (numMoved > 0) 394 System.arraycopy(elementData, index+1, elementData, index, 395 numMoved); 396 elementData[--size] = null; // Let gc do its work 397 398 return oldValue; 399 } 400 401 /** 402 * Removes the first occurrence of the specified element from this list, 403 * if it is present. If the list does not contain the element, it is 404 * unchanged. More formally, removes the element with the lowest index 405 * <tt>i</tt> such that 406 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> 407 * (if such an element exists). Returns <tt>true</tt> if this list 408 * contained the specified element (or equivalently, if this list 409 * changed as a result of the call). 410 * 411 * @param o element to be removed from this list, if present 412 * @return <tt>true</tt> if this list contained the specified element 413 */ 414 public boolean remove(Object o) { 415 if (o == null) { 416 for (int index = 0; index < size; index++) 417 if (elementData[index] == null) { 418 fastRemove(index); 419 return true; 420 } 421 } else { 422 for (int index = 0; index < size; index++) 423 if (o.equals(elementData[index])) { 424 fastRemove(index); 425 return true; 426 } 427 } 428 return false; 429 } 430 431 /* 432 * Private remove method that skips bounds checking and does not 433 * return the value removed. 434 */ 435 private void fastRemove(int index) { 436 modCount++; 437 int numMoved = size - index - 1; 438 if (numMoved > 0) 439 System.arraycopy(elementData, index+1, elementData, index, 440 numMoved); 441 elementData[--size] = null; // Let gc do its work 442 } 443 444 /** 445 * Removes all of the elements from this list. The list will 446 * be empty after this call returns. 447 */ 448 public void clear() { 449 modCount++; 450 451 // Let gc do its work 452 for (int i = 0; i < size; i++) 453 elementData[i] = null; 454 455 size = 0; 456 } 457 458 /** 459 * Appends all of the elements in the specified collection to the end of 460 * this list, in the order that they are returned by the 461 * specified collection's Iterator. The behavior of this operation is 462 * undefined if the specified collection is modified while the operation 463 * is in progress. (This implies that the behavior of this call is 464 * undefined if the specified collection is this list, and this 465 * list is nonempty.) 466 * 467 * @param c collection containing elements to be added to this list 468 * @return <tt>true</tt> if this list changed as a result of the call 469 * @throws NullPointerException if the specified collection is null 470 */ 471 public boolean addAll(Collection<? extends E> c) { 472 Object[] a = c.toArray(); 473 int numNew = a.length; 474 ensureCapacity(size + numNew); // Increments modCount 475 System.arraycopy(a, 0, elementData, size, numNew); 476 size += numNew; 477 return numNew != 0; 478 } 479 480 /** 481 * Inserts all of the elements in the specified collection into this 482 * list, starting at the specified position. Shifts the element 483 * currently at that position (if any) and any subsequent elements to 484 * the right (increases their indices). The new elements will appear 485 * in the list in the order that they are returned by the 486 * specified collection's iterator. 487 * 488 * @param index index at which to insert the first element from the 489 * specified collection 490 * @param c collection containing elements to be added to this list 491 * @return <tt>true</tt> if this list changed as a result of the call 492 * @throws IndexOutOfBoundsException {@inheritDoc} 493 * @throws NullPointerException if the specified collection is null 494 */ 495 public boolean addAll(int index, Collection<? extends E> c) { 496 if (index > size || index < 0) 497 throw new IndexOutOfBoundsException( 498 "Index: " + index + ", Size: " + size); 499 500 Object[] a = c.toArray(); 501 int numNew = a.length; 502 ensureCapacity(size + numNew); // Increments modCount 503 504 int numMoved = size - index; 505 if (numMoved > 0) 506 System.arraycopy(elementData, index, elementData, index + numNew, 507 numMoved); 508 509 System.arraycopy(a, 0, elementData, index, numNew); 510 size += numNew; 511 return numNew != 0; 512 } 513 514 /** 515 * Removes from this list all of the elements whose index is between 516 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. 517 * Shifts any succeeding elements to the left (reduces their index). 518 * This call shortens the list by <tt>(toIndex - fromIndex)</tt> elements. 519 * (If <tt>toIndex==fromIndex</tt>, this operation has no effect.) 520 * 521 * @param fromIndex index of first element to be removed 522 * @param toIndex index after last element to be removed 523 * @throws IndexOutOfBoundsException if fromIndex or toIndex out of 524 * range (fromIndex < 0 || fromIndex >= size() || toIndex 525 * > size() || toIndex < fromIndex) 526 */ 527 protected void removeRange(int fromIndex, int toIndex) { 528 modCount++; 529 int numMoved = size - toIndex; 530 System.arraycopy(elementData, toIndex, elementData, fromIndex, 531 numMoved); 532 533 // Let gc do its work 534 int newSize = size - (toIndex-fromIndex); 535 while (size != newSize) 536 elementData[--size] = null; 537 } 538 539 /** 540 * Checks if the given index is in range. If not, throws an appropriate 541 * runtime exception. This method does *not* check if the index is 542 * negative: It is always used immediately prior to an array access, 543 * which throws an ArrayIndexOutOfBoundsException if index is negative. 544 */ 545 private void RangeCheck(int index) { 546 if (index >= size) 547 throw new IndexOutOfBoundsException( 548 "Index: "+index+", Size: "+size); 549 } 550 551 /** 552 * Save the state of the <tt>ArrayList</tt> instance to a stream (that 553 * is, serialize it). 554 * 555 * @serialData The length of the array backing the <tt>ArrayList</tt> 556 * instance is emitted (int), followed by all of its elements 557 * (each an <tt>Object</tt>) in the proper order. 558 */ 559 private void writeObject(java.io.ObjectOutputStream s) 560 throws java.io.IOException{ 561 // Write out element count, and any hidden stuff 562 int expectedModCount = modCount; 563 s.defaultWriteObject(); 564 565 // Write out array length 566 s.writeInt(elementData.length); 567 568 // Write out all elements in the proper order. 569 for (int i=0; i<size; i++) 570 s.writeObject(elementData[i]); 571 572 if (modCount != expectedModCount) { 573 throw new ConcurrentModificationException(); 574 } 575 576 } 577 578 /** 579 * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is, 580 * deserialize it). 581 */ 582 private void readObject(java.io.ObjectInputStream s) 583 throws java.io.IOException, ClassNotFoundException { 584 // Read in size, and any hidden stuff 585 s.defaultReadObject(); 586 587 // Read in array length and allocate array 588 int arrayLength = s.readInt(); 589 Object[] a = elementData = new Object[arrayLength]; 590 591 // Read in all elements in the proper order. 592 for (int i=0; i<size; i++) 593 a[i] = s.readObject(); 594 } 595 } 596