arraylist.java

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/* ArrayList.java -- JDK1.2's answer to Vector; this is an array-backed
   implementation of the List interface
   Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.util;

import java.lang.reflect.Array;
import java.io.Serializable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

/**
 * An array-backed implementation of the List interface.  This implements
 * all optional list operations, and permits null elements, so that it is
 * better than Vector, which it replaces. Random access is roughly constant
 * time, and iteration is roughly linear time, so it is nice and fast, with
 * less overhead than a LinkedList.
 * <p>
 *
 * Each list has a capacity, and as the array reaches that capacity it
 * is automatically transferred to a larger array. You also have access to
 * ensureCapacity and trimToSize to control the backing array's size, avoiding
 * reallocation or wasted memory.
 * <p>
 *
 * ArrayList is not synchronized, so if you need multi-threaded access,
 * consider using:<br>
 * <code>List l = Collections.synchronizedList(new ArrayList(...));</code>
 * <p>
 *
 * The iterators are <i>fail-fast</i>, meaning that any structural
 * modification, except for <code>remove()</code> called on the iterator
 * itself, cause the iterator to throw a
 * {@link ConcurrentModificationException} rather than exhibit
 * non-deterministic behavior.
 *
 * @author Jon A. Zeppieri
 * @author Bryce McKinlay
 * @author Eric Blake <[e-mail]>
 * @see Collection
 * @see List
 * @see LinkedList
 * @see Vector
 * @see Collections#synchronizedList(List)
 * @see AbstractList
 * @status updated to 1.4
 */
public class ArrayList extends AbstractList
  implements List, RandomAccess, Cloneable, Serializable
{
  /**
   * Compatible with JDK 1.2
   */
  private static final long serialVersionUID = 8683452581122892189L;

  /**
   * The default capacity for new ArrayLists.
   */
  private static final int DEFAULT_CAPACITY = 16;

  /**
   * The number of elements in this list.
   * @serial the list size
   */
  private int size;

  /**
   * Where the data is stored.
   */
  private transient Object[] data;

  /**
   * Construct a new ArrayList with the supplied initial capacity.
   *
   * @param capacity initial capacity of this ArrayList
   * @throws IllegalArgumentException if capacity is negative
   */
  public ArrayList(int capacity)
  {
    // Must explicitly check, to get correct exception.
    if (capacity < 0)
      throw new IllegalArgumentException();
    data = new Object[capacity];
  }

  /**
   * Construct a new ArrayList with the default capcity (16).
   */
  public ArrayList()
  {
    this(DEFAULT_CAPACITY);
  }

  /**
   * Construct a new ArrayList, and initialize it with the elements
   * in the supplied Collection. The initial capacity is 110% of the
   * Collection's size.
   *
   * @param c the collection whose elements will initialize this list
   * @throws NullPointerException if c is null
   */
  public ArrayList(Collection c)
  {
    this((int) (c.size() * 1.1f));
    addAll(c);
  }

  /**
   * Trims the capacity of this List to be equal to its size;
   * a memory saver.
   */
  public void trimToSize()
  {
    // Not a structural change from the perspective of iterators on this list,
    // so don't update modCount.
    if (size != data.length)
      {
        Object[] newData = new Object[size];
        System.arraycopy(data, 0, newData, 0, size);
        data = newData;
      }
  }

  /**
   * Guarantees that this list will have at least enough capacity to
   * hold minCapacity elements. This implementation will grow the list to
   * max(current * 2, minCapacity) if (minCapacity &gt; current). The JCL says
   * explictly that "this method increases its capacity to minCap", while
   * the JDK 1.3 online docs specify that the list will grow to at least the
   * size specified.
   *
   * @param minCapacity the minimum guaranteed capacity
   */
  public void ensureCapacity(int minCapacity)
  {
    int current = data.length;

    if (minCapacity > current)
      {
        Object[] newData = new Object[Math.max(current * 2, minCapacity)];
        System.arraycopy(data, 0, newData, 0, size);
        data = newData;
      }
  }

  /**
   * Returns the number of elements in this list.
   *
   * @return the list size
   */
  public int size()
  {
    return size;
  }

  /**
   * Checks if the list is empty.
   *
   * @return true if there are no elements
   */
  public boolean isEmpty()
  {
    return size == 0;
  }

  /**
   * Returns true iff element is in this ArrayList.
   *
   * @param e the element whose inclusion in the List is being tested
   * @return true if the list contains e
   */
  public boolean contains(Object e)
  {
    return indexOf(e) != -1;
  }

  /**
   * Returns the lowest index at which element appears in this List, or
   * -1 if it does not appear.
   *
   * @param e the element whose inclusion in the List is being tested
   * @return the index where e was found
   */
  public int indexOf(Object e)
  {
    for (int i = 0; i < size; i++)
      if (equals(e, data[i]))
        return i;
    return -1;
  }

  /**
   * Returns the highest index at which element appears in this List, or
   * -1 if it does not appear.
   *
   * @param e the element whose inclusion in the List is being tested
   * @return the index where e was found
   */
  public int lastIndexOf(Object e)
  {
    for (int i = size - 1; i >= 0; i--)
      if (equals(e, data[i]))
        return i;
    return -1;
  }

  /**
   * Creates a shallow copy of this ArrayList (elements are not cloned).
   *
   * @return the cloned object
   */
  public Object clone()
  {
    ArrayList clone = null;
    try
      {
        clone = (ArrayList) super.clone();
        clone.data = (Object[]) data.clone();
      }
    catch (CloneNotSupportedException e)
      {
        // Impossible to get here.
      }
    return clone;
  }

  /**
   * Returns an Object array containing all of the elements in this ArrayList.
   * The array is independent of this list.
   *
   * @return an array representation of this list
   */
  public Object[] toArray()
  {
    Object[] array = new Object[size];
    System.arraycopy(data, 0, array, 0, size);
    return array;
  }

  /**
   * Returns an Array whose component type is the runtime component type of
   * the passed-in Array.  The returned Array is populated with all of the
   * elements in this ArrayList.  If the passed-in Array is not large enough
   * to store all of the elements in this List, a new Array will be created
   * and returned; if the passed-in Array is <i>larger</i> than the size
   * of this List, then size() index will be set to null.
   *
   * @param a the passed-in Array
   * @return an array representation of this list
   * @throws ArrayStoreException if the runtime type of a does not allow
   *         an element in this list
   * @throws NullPointerException if a is null
   */
  public Object[] toArray(Object[] a)
  {
    if (a.length < size)
      a = (Object[]) Array.newInstance(a.getClass().getComponentType(),
                                       size);