创建一个ArrayList的3个构造方法

/**     * Constructs an empty list with an initial capacity of ten.     */	 //方法一 有指定大小，默认size为10    public ArrayList() {        this(10);    }	/**     * 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     */	 // 方法二 指定size的大小    public ArrayList(int initialCapacity) {        super();        if (initialCapacity < 0)            throw new IllegalArgumentException("Illegal Capacity: "+                                               initialCapacity);        this.elementData = new Object[initialCapacity];    }		// 方法3，直接传入一个Collection的集合	/**     * 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
     c) {        elementData = c.toArray();        size = elementData.length;        // c.toArray might (incorrectly) not return Object[] (see 6260652)        if (elementData.getClass() != Object[].class)            elementData = Arrays.copyOf(elementData, size, Object[].class);    }

实用中几乎都是List list = new ArrayList（）这样了吧。