Vector源码阅读(JDK 8)

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Vector的内部实现和ArrayList形式上一致，因此其实现原理可以参考ArrayList。

下面说说Vector和ArrayList的不同之处：

1.属性增加了capacityIncrement:

   /**     * 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;

用于指定每次数组进行扩容的量，如果不指定或者指定为0，则每次按自身长度翻倍(2介绍)

2.扩容：

private void grow(int minCapacity) {     // overflow-conscious code     int oldCapacity = elementData.length;/** * 这段方法是和ArrayList不同的一个地方 * ArrayList是扩容至size / 2 * Vectors是扩容capacityIncrement或者翻倍 * 如果在构造函数中指定了capacityIncrement，则扩容capacityIncrement * 否则按原有的长度翻倍 */        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?                                         capacityIncrement : oldCapacity);          if (newCapacity - minCapacity < 0)            newCapacity = minCapacity;        if (newCapacity - MAX_ARRAY_SIZE > 0)            newCapacity = hugeCapacity(minCapacity);        elementData = Arrays.copyOf(elementData, newCapacity);    }

3.构造方法：

    /**     * 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     * @throws IllegalArgumentException if the specified initial capacity     *         is negative     * ~和ArrayList的一个构造函数相似，初始化了elementData的长度，不同的地方是增加了capacityIncrement     * 计算每次翻倍的量     */    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     * @throws IllegalArgumentException if the specified initial capacity     *         is negative * 和ArrayList的一个构造函数相似     */    public Vector(int initialCapacity) {        this(initialCapacity, 0);    }    /**     * Constructs an empty vector so that its internal data array     * has size {@code 10} 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<? extends E> c) {        elementData = c.toArray();        elementCount = elementData.length;        // c.toArray might (incorrectly) not return Object[] (see 6260652)        if (elementData.getClass() != Object[].class)            elementData = Arrays.copyOf(elementData, elementCount, Object[].class);    }

4.Vector方法都有synchronized修饰，因此是线程安全方法

~~~意义：
1.Vector是线程安全的，这是和ArrayList一个很大的区别。

2.Vector的扩容算法和ArrayList不一致，因此可以考虑好程序逻辑的前提下，适当地指定每次扩容的量和初始化数组的长度

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