Vectorスレッドの安全なArrayList

public class Vector<E>
    extends AbstractList<E>
    implements List<E>, 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 {@code Vector} object.
     * Components {@code elementData[0]} through
     * {@code elementData[elementCount-1]} 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;

/**
     * Removes the first occurrence of the specified element in this Vector
     * If the Vector does not contain the element, it is unchanged.  More
     * formally, removes the element with the lowest index i such that
     * {@code (o==null ? get(i)==null : o.equals(get(i)))} (if such
     * an element exists).
     *
     * @param o element to be removed from this Vector, if present
     * @return true if the Vector contained the specified element
     * @since 1.2
     */
    public boolean remove(Object o) {
        return removeElement(o);
    }

/**
     * 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
     * {@link #remove(Object)} method (which is part of the
     * {@link List} interface).
     *
     * @param   obj   the component to be removed
     * @return  {@code true} if the argument was a component of this
     *          vector; {@code false} otherwise.
     */
    public synchronized boolean removeElement(Object obj) {
	modCount++;
	int i = indexOf(obj);
	if (i >= 0) {
	    removeElementAt(i);
	    return true;
	}
	return false;
    }

/**
     * Returns the element at the specified position in this Vector.
     *
     * @param index index of the element to return
     * @return object at the specified index
     * @throws ArrayIndexOutOfBoundsException if the index is out of range
     *            ({@code index < 0 || index >= size()})
     * @since 1.2
     */
    public synchronized E get(int index) {
	if (index >= elementCount)
	    throw new ArrayIndexOutOfBoundsException(index);

	return (E)elementData[index];
    }

/**
     * Appends the specified element to the end of this Vector.
     *
     * @param e element to be appended to this Vector
     * @return {@code true} (as specified by {@link Collection#add})
     * @since 1.2
     */
    public synchronized boolean add(E e) {
	modCount++;
	ensureCapacityHelper(elementCount + 1);
	elementData[elementCount++] = e;
        return true;
    }

/**
     * 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 #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 = Arrays.copyOf(elementData, newCapacity);
	}
    }