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 。