Java 1.2 How-To/JavaHowTo.iso/3rdParty/jbuilder/unsupported/JDK1.2beta3/SOURCE/SRC.ZIP/java/util/Vector.java

Java Source | 1998-03-20 | 29.1 KB | 834 lines

/*
 * @(#)Vector.java    1.54 98/03/18
 *
 * Copyright 1994-1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */

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 JDK1.2, 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.
 *
 * @author  Lee Boynton
 * @author  Jonathan Payne
 * @version 1.54, 03/18/98
 * @see Collection
 * @see List
 * @see ArrayList
 * @see LinkedList
 * @since   JDK1.0
 */
public class Vector extends AbstractList implements List, 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.
     */
    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.
     */
    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 <code>0</code>, the capacity of the
     * vector is doubled each time it needs to grow.
     */
    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.
     *
     * @since   JDK1.2
     */
    public Vector(Collection c) {
    this((c.size()*110)/100);    // Allow 10% room for growth

    Iterator i = c.iterator();
    while (i.hasNext())
        elementData[elementCount++] = i.next();
    }

    /**
     * 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.
     */
    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 cector 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 nonpositive, 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) {
    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) {
    modCount++;
    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.
     */
    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 arary, kept in the field <tt>elementData</tt>
     *          of this vector.
     */
    public int capacity() {
    return elementData.length;
    }

    /**
     * Returns the number of components in this vector.
     *
     * @return  the number of components in this vector.
     */
    public 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 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 synchronized 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
     * the search at <code>index</code>, and testing for equality using
     * the <code>equals</code> method.
     *
     * @param   elem    an object.
     * @param   index   the index to start searching from.
     * @return  the index of the first occurrence of the object argument in
     *          this vector at position <code>index</code> or later in the
     *          vector, that is, the smallest value <tt>k</tt> such that
     *          <tt>elem.equals(elementData[k]) && (k >= index)</tt> is
     *          <tt>true</tt>; returns <code>-1</code> if the object is not
     *           found.
     * @see     Object#equals(Object)
     */
    public synchronized int indexOf(Object elem, int index) {
    if (elem == null) {
        for (int i = index ; i < elementCount ; i++)
        if (elementData[i]==null)
            return i;
    } else {
        for (int i = index ; i < elementCount ; i++)
        if (elem.equals(elementData[i]))
            return i;
    }
    return -1;
    }

    /**
     * Returns the index of the last occurrence of the specified object in
     * this vector.
     *
     * @param   elem   the desired component.
     * @return  the index of the last occurrence of the specified object in
     *          this vector, that is, the largest 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.
     */
    public int lastIndexOf(Object elem) {
    return lastIndexOf(elem, elementCount-1);
    }

    /**
     * Searches backwards for the specified object, starting from the
     * specified index, and returns an index to it.
     *
     * @param  elem    the desired component.
     * @param  index   the index to start searching from.
     * @return the index of the last occurrence of the specified object in this
     *          vector at position less than <code>index</code> in the
     *          vector, that is, the largest value <tt>k</tt> such that
     *          <tt>elem.equals(elementData[k]) && (k <= index)</tt> is
     *          <tt>true</tt>; <code>-1</code> if the object is not found.
     */
    public synchronized int lastIndexOf(Object elem, int index) {
    if (elem == null) {
        for (int i = index; i >= 0; i--)
        if (elementData[i]==null)
            return i;
    } else {
        for (int i = index; i >= 0; i--)
        if (elem.equals(elementData[i]))
            return i;
    }
    return -1;
    }

    /**
     * Returns the component at the specified index.
     * <p>
     * This method is identical in functionality to the get method
     * (which is part of the List interface).
     *
     * @param      index   an index into this vector.
     * @return     the component at the specified index.
     * @exception  ArrayIndexOutOfBoundsException  if the <tt>index</tt>
     *             is negative or not less than the current size of this
     *             <tt>Vector</tt> object.
     *             given.
     * @see       #get(int)
     * @see       List
     */
    public synchronized Object elementAt(int index) {
    if (index >= elementCount) {
        throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
    }
    /* Since try/catch is free, except when the exception is thrown,
       put in this extra try/catch to catch negative indexes and
       display a more informative error message.  This might not
       be appropriate, especially if we have a decent debugging
       environment - JP. */
    try {
        return elementData[index];
    } catch (ArrayIndexOutOfBoundsException e) {
        throw new ArrayIndexOutOfBoundsException(index + " < 0");
    }
    }

    /**
     * Returns the first component (the item at index <tt>0</tt>) of
     * this vector.
     *
     * @return     the first component of this vector.
     * @exception  NoSuchElementException  if this vector has no components.
     */
    public synchronized Object firstElement() {
    if (elementCount == 0) {
        throw new NoSuchElementException();
    }
    return elementData[0];
    }

    /**
     * Returns the last component of the vector.
     *
     * @return  the last component of the vector, i.e., the component at index
     *          <code>size() - 1</code>.
     * @exception  NoSuchElementException  if this vector is empty.
     */
    public synchronized Object lastElement() {
    if (elementCount == 0) {
        throw new NoSuchElementException();
    }
    return elementData[elementCount - 1];
    }

    /**
     * Sets the component at the specified <code>index</code> of this
     * vector to be the specified object. The previous component at that
     * position is discarded.
     * <p>
     * The index must be a value greater than or equal to <code>0</code>
     * and less than the current size of the vector.
     * <p>
     * This method is identical in functionality to the set method
     * (which is part of the List interface). Note that the set method reverses
     * the order of the parameters, to more closely match array usage.  Note
     * also that the set method returns the old value that was stored at the
     * specified position.
     *
     * @param      obj     what the component is to be set to.
     * @param      index   the specified index.
     * @exception  ArrayIndexOutOfBoundsException  if the index was invalid.
     * @see        #size()
     * @see        List
     * @see       set
     */
    public synchronized void setElementAt(Object obj, int index) {
    if (index >= elementCount) {
        throw new ArrayIndexOutOfBoundsException(index + " >= " +
                             elementCount);
    }
    elementData[index] = obj;
    }

    /**
     * Deletes the component at the specified index. Each component in
     * this vector with an index greater or equal to the specified
     * <code>index</code> is shifted downward to have an index one
     * smaller than the value it had previously. The size of this vector
     * is decreased by <tt>1</tt>.
     * <p>
     * The index must be a value greater than or equal to <code>0</code>
     * and less than the current size of the vector.
     * <p>
     * This method is identical in functionality to the remove method
     * (which is part of the List interface).  Note that the remove method
     * returns the old value that was stored at the specified position.
     *
     * @param      index   the index of the object to remove.
     * @exception  ArrayIndexOutOfBoundsException  if the index was invalid.
     * @see        #size()
     * @see       #remove(int)
     * @see       List
     */
    public synchronized void removeElementAt(int index) {
    modCount++;
    if (index >= elementCount) {
        throw new ArrayIndexOutOfBoundsException(index + " >= " +
                             elementCount);
    }
    else if (index < 0) {
        throw new ArrayIndexOutOfBoundsException(index);
    }
    int j = elementCount - index - 1;
    if (j > 0) {
        System.arraycopy(elementData, index + 1, elementData, index, j);
    }
    elementCount--;
    elementData[elementCount] = null; /* to let gc do its work */
    }

    /**
     * Inserts the specified object as a component in this vector at the
     * specified <code>index</code>. Each component in this vector with
     * an index greater or equal to the specified <code>index</code> is
     * shifted upward to have an index one greater than the value it had
     * previously.
     * <p>
     * The index must be a value greater than or equal to <code>0</code>
     * and less than or equal to the current size of the vector.
     * <p>
     * This method is identical in functionality to the add(Object, int) method
     * (which is part of the List interface). Note that the add method reverses
     * the order of the parameters, to more closely match array usage.
     *
     * @param      obj     the component to insert.
     * @param      index   where to insert the new component.
     * @exception  ArrayIndexOutOfBoundsException  if the index was invalid.
     * @see        #size()
     * @see       #add(Object, int)
     * @see       List
     */
    public synchronized void insertElementAt(Object obj, int index) {
    modCount++;
    if (index >= elementCount + 1) {
        throw new ArrayIndexOutOfBoundsException(index
                             + " > " + elementCount);
    }
    ensureCapacityHelper(elementCount + 1);
    System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
    elementData[index] = obj;
    elementCount++;
    }

    /**
     * Adds the specified component to the end of this vector,
     * increasing its size by one. The capacity of this vector is
     * increased if its size becomes greater than its capacity.
     * <p>
     * This method is identical in functionality to the add(Object) method
     * (which is part of the List interface).
     *
     * @param   obj   the component to be added.
     * @see       #add(Object)
     * @see       List
     */
    public synchronized void addElement(Object obj) {
    modCount++;
    ensureCapacityHelper(elementCount + 1);
    elementData[elementCount++] = obj;
    }

    /**
     * Removes the first (lowest-indexed) occurrence of the argument
     * from this vector. If the object is found in this vector, each
     * component in the vector with an index greater or equal to the
     * object's index is shifted downward to have an index one smaller
     * than the value it had previously.
     * <p>
     * This method is identical in functionality to the remove(Object)
     * method (which is part of the List interface).
     *
     * @param   obj   the component to be removed.
     * @return  <code>true</code> if the argument was a component of this
     *          vector; <code>false</code> otherwise.
     * @see    List#remove(Object)
     * @see    List
     */
    public synchronized boolean removeElement(Object obj) {
    modCount++;
    int i = indexOf(obj);
    if (i >= 0) {
        removeElementAt(i);
        return true;
    }
    return false;
    }

    /**
     * Removes all components from this vector and sets its size to zero.
     * <p>
     * This method is identical in functionality to the clear method
     * (which is part of the List interface).
     *
     * @see    clear
     * @see    List
     */
    public synchronized void removeAllElements() {
    modCount++;
    for (int i = 0; i < elementCount; i++) {
        elementData[i] = null;
    }
    elementCount = 0;
    }

    /**
     * Returns a clone of this vector. The copy will contain a
     * reference to a clone of the internal data array, not a reference
     * to the original internal data array of this <tt>Vector</tt> object.
     *
     * @return  a clone of this vector.
     */
    public synchronized Object clone() {
    try {
        Vector v = (Vector)super.clone();
        v.elementData = new Object[elementCount];
        System.arraycopy(elementData, 0, v.elementData, 0, elementCount);
        v.modCount = 0;
        return v;
    } catch (CloneNotSupportedException e) {
        // this shouldn't happen, since we are Cloneable
        throw new InternalError();
    }
    }

    /**
     * Returns an array containing all of the elements in this Vector
     * in the correct order.
     *
     * @since JDK1.2
     */
    public synchronized Object[] toArray() {
    Object[] result = new Object[elementCount];
    System.arraycopy(elementData, 0, result, 0, elementCount);
    return result;
    }


    // Positional Access Operations

    /**
     * Returns the element at the specified position in this Vector.
     *
     * @param index index of element to return.
     * @exception ArrayIndexOutOfBoundsException index is out of range (index
     *           < 0 || index >= size()).
     * @since JDK1.2
     */
    public synchronized Object get(int index) {
    if (index >= elementCount)
        throw new ArrayIndexOutOfBoundsException(index);

    return elementData[index];
    }

    /**
     * Replaces the element at the specified position in this Vector with the
     * specified element.
     *
     * @param index index of element to replace.
     * @param element element to be stored at the specified position.
     * @return the element previously at the specified position.
     * @exception ArrayIndexOutOfBoundsException index out of range
     *          (index < 0 || index >= size()).
     * @exception IllegalArgumentException fromIndex > toIndex.
     * @since JDK1.2
     */
    public synchronized Object set(int index, Object element) {
    if (index >= elementCount)
        throw new ArrayIndexOutOfBoundsException(index);

    Object oldValue = elementData[index];
    elementData[index] = element;
    return oldValue;
    }

    /**
     * Inserts the specified element at the specified position in this Vector.
     * Shifts the element currently at that position (if any) and any
     * subsequent elements to the right (adds one to their indices).
     *
     * @param index index at which the specified element is to be inserted.
     * @param element element to be inserted.
     * @exception ArrayIndexOutOfBoundsException index is out of range
     *          (index < 0 || index > size()).
     * @since JDK1.2
     */
    public synchronized void add(int index, Object element) {
    if (index > elementCount)
        throw new ArrayIndexOutOfBoundsException(index);

    ensureCapacityHelper(elementCount+1);     // Increments modCount
    System.arraycopy(elementData, index, elementData, index + 1,
             elementCount - index);
    elementData[index] = element;
    elementCount++;
    }

    /**
     * Removes the element at the specified position in this Vector.
     * shifts any subsequent elements to the left (subtracts one from their
     * indices).  Returns the element that was removed from the Vector.
     *
     * @exception ArrayIndexOutOfBoundsException index out of range (index
     *           < 0 || index >= size()).
     * @param index the index of the element to removed.
     * @since JDK1.2
     */
    public synchronized Object remove(int index) {
    modCount++;
    if (index >= elementCount)
        throw new ArrayIndexOutOfBoundsException(index);
    Object oldValue = elementData[index];

    int numMoved = elementCount - index - 1;
    if (numMoved > 0)
        System.arraycopy(elementData, index+1, elementData, index,
                 numMoved);
    elementData[--elementCount] = null; // Let gc do its work

    return oldValue;
    }

    /**
     * Removes all of the elements from this Vector.  The Vector will
     * be empty after this call returns (unless it throws an exception).
     *
     * @exception UnsupportedOperationException clear is not supported
     *           by this Set.
     * @since JDK1.2
     */
    public synchronized void clear() {
    modCount++;

    // Let gc do its work
    for (int i = 0; i < elementCount; i++)
        elementData[i] = null;

    elementCount = 0;
    }

    /**
     * Appends all of the elements in the specified Collection to the end of
     * this this Vector, in the order that they are returned by the specified
     * Collection's Iterator.  The behavior of this operation is undefined if
     * the specified Collection is modified while the operation is in progress.
     * (This implies that the behavior of this call is undefined if the the
     * specified Collection is this Vector, and this Vector is nonempty.)
     *
     * @param index index at which to insert first element
     *              from the specified collection.
     * @param c elements to be inserted into this Vector.
     * @exception ArrayIndexOutOfBoundsException index out of range (index
     *          < 0 || index > size()).
     * @since JDK1.2
     */
    public synchronized boolean addAll(Collection c) {
    modCount++;
    int numNew = c.size();
    ensureCapacityHelper(elementCount + numNew);

    Iterator e = c.iterator();
    for (int i=0; i<numNew; i++)
        elementData[elementCount++] = e.next();

    return numNew != 0;
    }

    /**
     * Removes from this Vector all of the elements whose index is between
     * fromIndex, inclusive and toIndex, exclusive.  Shifts any succeeding
     * elements to the left (reduces their index).
     * This call shortens the Vector by (toIndex - fromIndex) elements.  (If
     * toIndex==fromIndex, this operation has no effect.)
     *
     * @param fromIndex index of first element to be removed.
     * @param fromIndex index after last element to be removed.
     * @exception ArrayIndexOutOfBoundsException fromIndex or toIndex out of
     *          range (fromIndex < 0 || fromIndex >= size() || toIndex
     *          > size() || toIndex < fromIndex).
     * @since JDK1.2
     */
    public synchronized void removeRange(int fromIndex, int toIndex) {
    modCount++;
    if (fromIndex < 0 || fromIndex >= elementCount ||
        toIndex > elementCount || toIndex < fromIndex)
        throw new ArrayIndexOutOfBoundsException();

    int numMoved = elementCount - toIndex;
    if (numMoved > 0)
        System.arraycopy(elementData, toIndex, elementData, fromIndex,
                 numMoved);

    // Let gc do its work
    int newElementCount = elementCount - (toIndex-fromIndex);
    while (elementCount != newElementCount)
        elementData[--elementCount] = null;
    }

    /**
     * Inserts all of the elements in in the specified Collection into this
     * Vector at the specified position.  Shifts the element currently at
     * that position (if any) and any subsequent elements to the right
     * (increases their indices).  The new elements will appear in the Vector
     * in the order that they are returned by the specified Collection's
     * iterator.
     *
     * @param index index at which to insert first element
     *            from the specified collection.
     * @param c elements to be inserted into this Vector.
     * @exception ArrayIndexOutOfBoundsException index out of range (index
     *          < 0 || index > size()).
     * @since JDK1.2
     */
    public synchronized boolean addAll(int index, Collection c) {
    modCount++;
    if (index < 0 || index > elementCount)
        throw new ArrayIndexOutOfBoundsException(index);

    int numNew = c.size();
    ensureCapacityHelper(elementCount + numNew);

    int numMoved = elementCount - index;
    if (numMoved > 0)
        System.arraycopy(elementData, index, elementData, index + numNew,
                 numMoved);

    Iterator e = c.iterator();
    for (int i=0; i<numNew; i++)
        elementData[index++] = e.next();

    elementCount += numNew;
    return numNew != 0;
    }
}