Java源碼閱讀-Vector

Vector的實現和ArrayList十分類似，不同的是Vector是線程安全的，很多方法都用synchronized修飾。

還有一個不同點是Vector每次擴容都是增加1倍，而ArrayList則是增加50%。

/**
     * 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) { // add方法，是同步的
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
    }

/**
     * 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.
     *
     * @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index >= size()})
     * @param index the index of the element to be removed
     * @return element that was removed
     * @since 1.2
     */
    public synchronized E remove(int index) { // remove方法，也是同步的
        modCount++;
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);
        E 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;
    }