JAVA入门学习 —集合的增删改查

 @Test
    public void test02() {
        List<Object> of = new ArrayList<>(List.of(1, 2, 3, 4, 5, 6));
        //输出集合 --> [1, 2, 3, 4, 5, 6]
        System.out.println(of);
        //给原集合增加一个元素7 --> [1, 2, 3, 4, 5, 6, 7]
        of.add(7);
        System.out.println(of);
        //将该集合下标为2的元素修改为30 --> [1, 2, 30, 4, 5, 6, 7]
        of.set(2, 30);
        System.out.println(of);
        //删除该集合下标为1的元素 --> [1, 30, 4, 5, 6, 7]
        of.remove(1);
        System.out.println(of);
        //增加该集合下标为3的元素为20 --> [1, 30, 4, 20, 5, 6, 7]
        of.add(3, 20);
        System.out.println(of);
        //查询该集合下标为2的元素的值为 --> 4
        System.out.println(of.get(2));
    }