ArrayList a = new ArrayList();
        // 往ArrayList中添加元素
        a.add("a");
        a.add("b");
        a.add("c");
        a.add("d");
        System.out.println(a);
        // 获得Iterator对象
        Iterator it = a.iterator();
        it.next();
        it.remove();
        System.out.println(a);
        it.next();
        it.remove();
        System.out.println(a);