##   ArrayList 

**ArrayList**

```java
   /**
     * 
     */
    private static final int DEFAULT_CAPACITY = 10;
    

    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

    /**
     *10()
     */
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }
    
    /**
     * 
     */
    public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {//0
            //initialCapacity
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {//0
            //
            this.elementData = EMPTY_ELEMENTDATA;
        } else {//0
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }


   /**
    *collection
    *nullthrows NullPointerException 
    */
     public ArrayList(Collection