ArrayList和Vector区别

  /**
     * Constructs an empty list with an initial capacity of ten.
     * 构造一个默认初始容量为10的list 
     */
    public ArrayList() {
        super();
        this.elementData = EMPTY_ELEMENTDATA;
    }

    /**
     * 构造一个指定默认长度的list initialCapacity 不能小于0;
     * Constructs an empty list with the specified initial capacity.
     *
     * @param  initialCapacity  the initial capacity of the list
     * @throws IllegalArgumentException if the specified initial capacity
     *         is negative
     */
    public ArrayList(int initialCapacity) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        this.elementData = new Object[initialCapacity];
    }




 /**  构造一个包含collection 元素的list
     * Constructs a list 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 list
     * @throws NullPointerException if the specified collection is null
     */
    public ArrayList(Collection<? extends E> c) {
      ...
    }

//构造一个指定默认长度的list
  public Vector(int initialCapacity) {
        this(initialCapacity, 0);
    }
 //构造一个默认初始容量为10的list 
  public Vector() {
        this(10);
    }
  //构造一个包含collection 元素的list
  public Vector(Collection<? extends E> c) {
        ...
    }
//区别在于可以设置capacityIncrement
 public Vector(int initialCapacity, int capacityIncrement) {
        super();
       ...
    }

    public boolean add(E e) {  
        ensureCapacityInternal(size + 1);  // Increments modCount!!  
        elementData[size++] = e;  
        return true;  
    }  

    private void ensureCapacityInternal(int minCapacity) {  
        modCount++;  
        // overflow-conscious code  

        //如果添加一个元素之后，新容器的大小大于容器的容量，那么就无法存值了，需要扩充空间  
        if (minCapacity - elementData.length > 0)  

            grow(minCapacity);  
    }  

    private void grow(int minCapacity) {  
        // overflow-conscious code  
        int oldCapacity = elementData.length;  
        int newCapacity = oldCapacity + (oldCapacity >> 1); //扩充的空间增加原来的50%（即是原来的1.5倍）  
        if (newCapacity - minCapacity < 0) //如果容器扩容之后还是不够，那么干脆直接将minCapacity设为容器的大小  
            newCapacity = minCapacity;  
        if (newCapacity - MAX_ARRAY_SIZE > 0) //如果扩充的容器太大了的话，那么就执行hugeCapacity  
            newCapacity = hugeCapacity(minCapacity);  
        // minCapacity is usually close to size, so this is a win:  
        elementData = Arrays.copyOf(elementData, newCapacity);  
    } 

     public synchronized boolean add(E e) {  
         modCount++;  
         ensureCapacityHelper(elementCount + 1);  
         elementData[elementCount++] = e;  
         return true;  
     }  

     private void ensureCapacityHelper(int minCapacity) {  
         // overflow-conscious code  
         if (minCapacity - elementData.length > 0)  
             grow(minCapacity);  
     }  

     private void grow(int minCapacity) {  
         // overflow-conscious code  
         int oldCapacity = elementData.length;  
         int newCapacity = oldCapacity + ((capacityIncrement > 0) ?  
                                          capacityIncrement : oldCapacity);  

         /** 

         这个扩容需要做个判断：如果容量增量初始化的不是0，即使用的public Vector(int initialCapacity,int capacityIncrement) 

         构造方法进行的初始化，那么扩容的容量是(oldCapacity+capacityIncrement)，就是原来的容量加上容量增量的值； 

         如果没有设置容量增量，那么扩容后的容量就是(oldCapacity+oldCapacity)，就是原来容量的二倍。 

         **/  

         if (newCapacity - minCapacity < 0)  
             newCapacity = minCapacity;  
         if (newCapacity - MAX_ARRAY_SIZE > 0)  
             newCapacity = hugeCapacity(minCapacity);  
         elementData = Arrays.copyOf(elementData, newCapacity);  
     }