vector.java

java源代码 请看看啊 提点宝贵的意见

/*
 * @(#)Vector.java	1.89 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;

/**
 * The <code>Vector</code> class implements a growable array of 
 * objects. Like an array, it contains components that can be 
 * accessed using an integer index. However, the size of a 
 * <code>Vector</code> can grow or shrink as needed to accommodate 
 * adding and removing items after the <code>Vector</code> has been created.<p>
 *
 * Each vector tries to optimize storage management by maintaining a 
 * <code>capacity</code> and a <code>capacityIncrement</code>. The 
 * <code>capacity</code> is always at least as large as the vector 
 * size; it is usually larger because as components are added to the 
 * vector, the vector's storage increases in chunks the size of 
 * <code>capacityIncrement</code>. An application can increase the 
 * capacity of a vector before inserting a large number of 
 * components; this reduces the amount of incremental reallocation. <p>
 *
 * As of the Java 2 platform v1.2, this class has been retrofitted to
 * implement List, so that it becomes a part of Java's collection framework.
 * Unlike the new collection implementations, Vector is synchronized.<p>
 *
 * The Iterators returned by Vector's iterator and listIterator
 * methods are <em>fail-fast</em>: if the Vector is structurally modified
 * at any time after the Iterator is created, in any way except through the
 * Iterator's own remove or add methods, the Iterator will throw a
 * ConcurrentModificationException.  Thus, in the face of concurrent
 * modification, the Iterator fails quickly and cleanly, rather than risking
 * arbitrary, non-deterministic behavior at an undetermined time in the future.
 * The Enumerations returned by Vector's elements method are <em>not</em>
 * fail-fast.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:  <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i><p>
 *
 * This class is a member of the 
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author  Lee Boynton
 * @author  Jonathan Payne
 * @version 1.89, 01/23/03
 * @see Collection
 * @see List
 * @see ArrayList
 * @see LinkedList
 * @since   JDK1.0
 */
public class Vector extends AbstractList
        implements List, RandomAccess, Cloneable, java.io.Serializable
{
    /**
     * The array buffer into which the components of the vector are
     * stored. The capacity of the vector is the length of this array buffer, 
     * and is at least large enough to contain all the vector's elements.<p>
     *
     * Any array elements following the last element in the Vector are null.
     *
     * @serial
     */
    protected Object elementData[];

    /**
     * The number of valid components in this <tt>Vector</tt> object. 
     * Components <tt>elementData[0]</tt> through 
     * <tt>elementData[elementCount-1]</tt> are the actual items.
     *
     * @serial
     */
    protected int elementCount;

    /**
     * The amount by which the capacity of the vector is automatically 
     * incremented when its size becomes greater than its capacity.  If 
     * the capacity increment is less than or equal to zero, the capacity
     * of the vector is doubled each time it needs to grow.
     *
     * @serial
     */
    protected int capacityIncrement;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = -2767605614048989439L;

    /**
     * Constructs an empty vector with the specified initial capacity and
     * capacity increment. 
     *
     * @param   initialCapacity     the initial capacity of the vector.
     * @param   capacityIncrement   the amount by which the capacity is
     *                              increased when the vector overflows.
     * @exception IllegalArgumentException if the specified initial capacity
     *               is negative
     */
    public Vector(int initialCapacity, int capacityIncrement) {
	super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
	this.elementData = new Object[initialCapacity];
	this.capacityIncrement = capacityIncrement;
    }

    /**
     * Constructs an empty vector with the specified initial capacity and 
     * with its capacity increment equal to zero.
     *
     * @param   initialCapacity   the initial capacity of the vector.
     * @exception IllegalArgumentException if the specified initial capacity
     *               is negative
     */
    public Vector(int initialCapacity) {
	this(initialCapacity, 0);
    }

    /**
     * Constructs an empty vector so that its internal data array 
     * has size <tt>10</tt> and its standard capacity increment is 
     * zero. 
     */
    public Vector() {
	this(10);
    }

    /**
     * Constructs a vector containing the elements of the specified
     * collection, in the order they are returned by the collection's
     * iterator.
     *
     * @param c the collection whose elements are to be placed into this
     *       vector.
     * @throws NullPointerException if the specified collection is null.
     * @since   1.2
     */
    public Vector(Collection c) {
        elementCount = c.size();
        // 10% for growth
        elementData = new Object[
                      (int)Math.min((elementCount*110L)/100,Integer.MAX_VALUE)]; 
        c.toArray(elementData);
    }

    /**
     * Copies the components of this vector into the specified array. The 
     * item at index <tt>k</tt> in this vector is copied into component 
     * <tt>k</tt> of <tt>anArray</tt>. The array must be big enough to hold 
     * all the objects in this vector, else an 
     * <tt>IndexOutOfBoundsException</tt> is thrown.
     *
     * @param   anArray   the array into which the components get copied.
     * @throws  NullPointerException if the given array is null.
     */
    public synchronized void copyInto(Object anArray[]) {
	System.arraycopy(elementData, 0, anArray, 0, elementCount);
    }

    /**
     * Trims the capacity of this vector to be the vector's current 
     * size. If the capacity of this vector is larger than its current 
     * size, then the capacity is changed to equal the size by replacing 
     * its internal data array, kept in the field <tt>elementData</tt>, 
     * with a smaller one. An application can use this operation to 
     * minimize the storage of a vector. 
     */
    public synchronized void trimToSize() {
	modCount++;
	int oldCapacity = elementData.length;
	if (elementCount < oldCapacity) {
	    Object oldData[] = elementData;
	    elementData = new Object[elementCount];
	    System.arraycopy(oldData, 0, elementData, 0, elementCount);
	}
    }

    /**
     * Increases the capacity of this vector, if necessary, to ensure 
     * that it can hold at least the number of components specified by 
     * the minimum capacity argument.
     *
     * <p>If the current capacity of this vector is less than
     * <tt>minCapacity</tt>, then its capacity is increased by replacing its
     * internal data array, kept in the field <tt>elementData</tt>, with a
     * larger one.  The size of the new data array will be the old size plus
     * <tt>capacityIncrement</tt>, unless the value of
     * <tt>capacityIncrement</tt> is less than or equal to zero, in which case
     * the new capacity will be twice the old capacity; but if this new size
     * is still smaller than <tt>minCapacity</tt>, then the new capacity will
     * be <tt>minCapacity</tt>.
     *
     * @param minCapacity the desired minimum capacity.
     */
    public synchronized void ensureCapacity(int minCapacity) {
	modCount++;
	ensureCapacityHelper(minCapacity);
    }
    
    /**
     * This implements the unsynchronized semantics of ensureCapacity.
     * Synchronized methods in this class can internally call this 
     * method for ensuring capacity without incurring the cost of an 
     * extra synchronization.
     *
     * @see java.util.Vector#ensureCapacity(int)
     */ 
    private void ensureCapacityHelper(int minCapacity) {
	int oldCapacity = elementData.length;
	if (minCapacity > oldCapacity) {
	    Object oldData[] = elementData;
	    int newCapacity = (capacityIncrement > 0) ?
		(oldCapacity + capacityIncrement) : (oldCapacity * 2);
    	    if (newCapacity < minCapacity) {
		newCapacity = minCapacity;
	    }
	    elementData = new Object[newCapacity];
	    System.arraycopy(oldData, 0, elementData, 0, elementCount);
	}
    }

    /**
     * Sets the size of this vector. If the new size is greater than the 
     * current size, new <code>null</code> items are added to the end of 
     * the vector. If the new size is less than the current size, all 
     * components at index <code>newSize</code> and greater are discarded.
     *
     * @param   newSize   the new size of this vector.
     * @throws  ArrayIndexOutOfBoundsException if new size is negative.
     */
    public synchronized void setSize(int newSize) {
	modCount++;
	if (newSize > elementCount) {
	    ensureCapacityHelper(newSize);
	} else {
	    for (int i = newSize ; i < elementCount ; i++) {
		elementData[i] = null;
	    }
	}
	elementCount = newSize;
    }

    /**
     * Returns the current capacity of this vector.
     *
     * @return  the current capacity (the length of its internal 
     *          data array, kept in the field <tt>elementData</tt> 
     *          of this vector).
     */
    public synchronized int capacity() {
	return elementData.length;
    }

    /**
     * Returns the number of components in this vector.
     *
     * @return  the number of components in this vector.
     */
    public synchronized int size() {
	return elementCount;
    }

    /**
     * Tests if this vector has no components.
     *
     * @return  <code>true</code> if and only if this vector has 
     *          no components, that is, its size is zero;
     *          <code>false</code> otherwise.
     */
    public synchronized boolean isEmpty() {
	return elementCount == 0;
    }

    /**
     * Returns an enumeration of the components of this vector. The 
     * returned <tt>Enumeration</tt> object will generate all items in 
     * this vector. The first item generated is the item at index <tt>0</tt>, 
     * then the item at index <tt>1</tt>, and so on. 
     *
     * @return  an enumeration of the components of this vector.
     * @see     Enumeration
     * @see     Iterator
     */
    public Enumeration elements() {
	return new Enumeration() {
	    int count = 0;

	    public boolean hasMoreElements() {
		return count < elementCount;
	    }

	    public Object nextElement() {
		synchronized (Vector.this) {
		    if (count < elementCount) {
			return elementData[count++];
		    }
		}
		throw new NoSuchElementException("Vector Enumeration");
	    }
	};
    }

    /**
     * Tests if the specified object is a component in this vector.
     *
     * @param   elem   an object.
     * @return  <code>true</code> if and only if the specified object 
     * is the same as a component in this vector, as determined by the 
     * <tt>equals</tt> method; <code>false</code> otherwise.
     */
    public boolean contains(Object elem) {
	return indexOf(elem, 0) >= 0;
    }

    /**
     * Searches for the first occurence of the given argument, testing 
     * for equality using the <code>equals</code> method. 
     *
     * @param   elem   an object.
     * @return  the index of the first occurrence of the argument in this
     *          vector, that is, the smallest value <tt>k</tt> such that 
     *          <tt>elem.equals(elementData[k])</tt> is <tt>true</tt>; 
     *          returns <code>-1</code> if the object is not found.
     * @see     Object#equals(Object)
     */
    public int indexOf(Object elem) {
	return indexOf(elem, 0);
    }

    /**
     * Searches for the first occurence of the given argument, beginning