java1.7集合源码阅读: Vector

 Vector是List接口的另一实现，有非常长的历史了，从jdk1.0开始就有Vector了，先于ArrayList出现，与ArrayList的最大区别是：Vector 是线程安全的，简单浏览一下Vector:

类定义：

public class Vector<E>
    extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable

Vector支持快速随机访问，和arrayList一样。

Vector 初始容量为10，支持自定义每次扩容长度，如果不自定义扩容长度，那么默认扩容后的长度是原来的2倍。

 /**
     * 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
     */
    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
     */
    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);
    }

Vector最大的特点是Vector内部基本上都使用了synchronized进行同步或者调用使用了 synchronized同步关键字的方法：

   /**
     * Returns {@code true} if this vector contains the specified element.
     * More formally, returns {@code true} if and only if this vector
     * contains at least one element {@code e} such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o element whose presence in this vector is to be tested
     * @return {@code true} if this vector contains the specified element
     */
    public boolean contains(Object o) {
        return indexOf(o, 0) >= 0;
    }

    /**
     * Returns the index of the first occurrence of the specified element
     * in this vector, or -1 if this vector does not contain the element.
     * More formally, returns the lowest index {@code i} such that
     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
     * or -1 if there is no such index.
     *
     * @param o element to search for
     * @return the index of the first occurrence of the specified element in
     *         this vector, or -1 if this vector does not contain the element
     */
    public int indexOf(Object o) {
        return indexOf(o, 0);
    }

    /**
     * Returns the index of the first occurrence of the specified element in
     * this vector, searching forwards from {@code index}, or returns -1 if
     * the element is not found.
     * More formally, returns the lowest index {@code i} such that
     * <tt>(i&nbsp;&gt;=&nbsp;index&nbsp;&amp;&amp;&nbsp;(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i))))</tt>,
     * or -1 if there is no such index.
     *
     * @param o element to search for
     * @param index index to start searching from
     * @return the index of the first occurrence of the element in
     *         this vector at position {@code index} or later in the vector;
     *         {@code -1} if the element is not found.
     * @throws IndexOutOfBoundsException if the specified index is negative
     * @see     Object#equals(Object)
     */
    public synchronized int indexOf(Object o, int index) {
        if (o == null) {
            for (int i = index ; i < elementCount ; i++)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = index ; i < elementCount ; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

    /**
     * Returns the index of the last occurrence of the specified element
     * in this vector, or -1 if this vector does not contain the element.
     * More formally, returns the highest index {@code i} such that
     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
     * or -1 if there is no such index.
     *
     * @param o element to search for
     * @return the index of the last occurrence of the specified element in
     *         this vector, or -1 if this vector does not contain the element
     */
    public synchronized int lastIndexOf(Object o) {
        return lastIndexOf(o, elementCount-1);
    }

    /**
     * Returns the index of the last occurrence of the specified element in
     * this vector, searching backwards from {@code index}, or returns -1 if
     * the element is not found.
     * More formally, returns the highest index {@code i} such that
     * <tt>(i&nbsp;&lt;=&nbsp;index&nbsp;&amp;&amp;&nbsp;(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i))))</tt>,
     * or -1 if there is no such index.
     *
     * @param o element to search for
     * @param index index to start searching backwards from
     * @return the index of the last occurrence of the element at position
     *         less than or equal to {@code index} in this vector;
     *         -1 if the element is not found.
     * @throws IndexOutOfBoundsException if the specified index is greater
     *         than or equal to the current size of this vector
     */
    public synchronized int lastIndexOf(Object o, int index) {
        if (index >= elementCount)
            throw new IndexOutOfBoundsException(index + " >= "+ elementCount);

        if (o == null) {
            for (int i = index; i >= 0; i--)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = index; i >= 0; i--)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

Vector 的实现实际上跟ArrayList差别不大，ArrayList可参考 java1.7集合源码阅读：ArrayList 。