public class ArrayList {

    public int index = 0;

    Object[] objects = new Object[2];

    public void add(Object o) {

        //当index超出最初定义数组的长度时，自动扩容

        if(index == objects.length){

            System.out.println("extend................");

            Object[] newObjects = new Object[objects.length * 2];

            for (int i = 0; i < index; i++) newObjects[i] = objects[i];

            objects = newObjects;

        }

        objects[index] = o;

        index++;

    }

    public int size(){ return index; }

    public int get(int i) {return (int)objects[i]; }

    public static void main(String[] args) {

        ArrayList a = new ArrayList();

        a.add(23);

        a.add(67);

        a.add(98);

        a.add(989);

        a.add(9897);

        for (int i = 0; i < a.size(); i++)

            System.out.println(a.get(i));

//        for (Integer abc : a) {

//            System.out.println(abc);

//        }

    }

}