Double a = 3.14;
        System.out.println(Math.round(a));  // 3
        System.out.println(Math.ceil(a));  // 4.0
        System.out.println(Math.floor(a));  //  3.0

        Double b = 3.84;
        System.out.println(Math.round(b)); // 4
        System.out.println(Math.ceil(b));// 4.0
        System.out.println(Math.floor(b));// 3.0

Math.round 四舍五入
Math.ceil 向上取整
Math.floor 向下取整