- 001
/* - 002
* @(#)ArrayList.java 1.56 06/04/21 - 003 *
- 004 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
- 005 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- 006
*/ - 007
- 008package java.util;
- 009
- 010/**
- 011 * Resizable-array implementation of the <tt>List</tt> interface. Implements
- 012 * all optional list operations, and permits all elements, including
- 013 * <tt>null</tt>. In addition to implementing the <tt>List</tt> interface,
- 014 * this class provides methods to manipulate the size of the array that is
- 015 * used internally to store the list. (This class is roughly equivalent to
- 016 * <tt>Vector</tt>, except that it is unsynchronized.)<p>
- 017 *
- 018 * The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>,
- 019 * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant
- 020 * time. The <tt>add</tt> operation runs in <i>amortized constant time</i>,
- 021 * that is, adding n elements requires O(n) time. All of the other operations
- 022 * run in linear time (roughly speaking). The constant factor is low compared
- 023 * to that for the <tt>LinkedList</tt> implementation.<p>
- 024 *
- 025 * Each <tt>ArrayList</tt> instance has a <i>capacity</i>. The capacity is
- 026 * the size of the array used to store the elements in the list. It is always
- 027 * at least as large as the list size. As elements are added to an ArrayList,
- 028 * its capacity grows automatically. The details of the growth policy are not
- 029 * specified beyond the fact that adding an element has constant amortized
- 030 * time cost.<p>
- 031 *
- 032 * An application can increase the capacity of an <tt>ArrayList</tt> instance
- 033 * before adding a large number of elements using the <tt>ensureCapacity</tt>
- 034 * operation. This may reduce the amount of incremental reallocation.
- 035 *
- 036 * <p><strong>Note that this implementation is not synchronized.</strong>
- 037 * If multiple threads access an <tt>ArrayList</tt> instance concurrently,
- 038 * and at least one of the threads modifies the list structurally, it
- 039 * <i>must</i> be synchronized externally. (A structural modification is
- 040 * any operation that adds or deletes one or more elements, or explicitly
- 041 * resizes the backing array; merely setting the value of an element is not
- 042 * a structural modification.) This is typically accomplished by
- 043 * synchronizing on some object that naturally encapsulates the list.
- 044 *
- 045 * If no such object exists, the list should be "wrapped" using the
- 046 * {@link Collections#synchronizedList Collections.synchronizedList}
- 047 * method. This is best done at creation time, to prevent accidental
- 048 * unsynchronized access to the list:<pre>
- 049 * List list = Collections.synchronizedList(new ArrayList(...));</pre>
- 050 *
- 051 * <p>The iterators returned by this class's <tt>iterator</tt> and
- 052 * <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is
- 053 * structurally modified at any time after the iterator is created, in any way
- 054 * except through the iterator's own <tt>remove</tt> or <tt>add</tt> methods,
- 055 * the iterator will throw a {@link ConcurrentModificationException}. Thus, in
- 056 * the face of concurrent modification, the iterator fails quickly and cleanly,
- 057 * rather than risking arbitrary, non-deterministic behavior at an undetermined
- 058 * time in the future.<p>
- 059 *
- 060 * Note that the fail-fast behavior of an iterator cannot be guaranteed
- 061 * as it is, generally speaking, impossible to make any hard guarantees in the
- 062 * presence of unsynchronized concurrent modification. Fail-fast iterators
- 063 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
- 064 * Therefore, it would be wrong to write a program that depended on this
- 065 * exception for its correctness: <i>the fail-fast behavior of iterators
- 066 * should be used only to detect bugs.</i><p>
- 067 *
- 068 * This class is a member of the
- 069 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
- 070 * Java Collections Framework</a>.
- 071 *
- 072 * @author Josh Bloch
- 073 * @author Neal Gafter
- 074 * @version 1.56, 04/21/06
- 075 * @see Collection
- 076 * @see List
- 077 * @see LinkedList
- 078 * @see Vector
- 079 * @since 1.2
- 080 */
- 081
- 082public class ArrayList<E> extends AbstractList<E>
- 083 implements List<E>, RandomAccess, Cloneable, java.io.Serializable
- 084{
- 085 private static final long serialVersionUID = 8683452581122892189L;
- 086
- 087 /**
- 088 * The array buffer into which the elements of the ArrayList are stored.
- 089 * The capacity of the ArrayList is the length of this array buffer.
- 090 */
- 091 private transient Object[] elementData;
- 092
- 093 /**
- 094 * The size of the ArrayList (the number of elements it contains).
- 095 *
- 096 * @serial
- 097 */
- 098 private int size;
- 099
- 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}
