a=3.45
b=5.21

a=Math.ceil(a)
b=Math.floor(b)

转化后得a=4 b=5

public class CeilAndFloor {
public static void main(String[] args) {
/*
这两个宝贝函数的主要任务是截掉小数以后的位数.
区别是: floor总是把数字变得越来越小，而ceil总是把数字变大。
其实名字可以理解floor是地板，ceil是天花板。
*/


System.out.println("==============Math.floor()==============");
System.out.println("Math.floor(99.1) = " + Math.floor(99.1));
System.out.println("Math.floor(-99.1) = " + Math.floor(-99.1));
System.out.println("Math.floor(99.9) = " + Math.floor(99.9));
System.out.println("Math.floor(-99.9) = " + Math.floor(-99.9));

System.out.println("\n\n==============Math.ceil()==============");
System.out.println("Math.ceil(99.1) = " + Math.ceil(99.1));
System.out.println("Math.ceil(-99.1) = " + Math.ceil(-99.1));
System.out.println("Math.ceil(99.9) = " + Math.ceil(99.9));
System.out.println("Math.ceil(-99.9) = " + Math.ceil(-99.9));

}
}

结果
==============Math.floor()==============
Math.floor(99.1) = 99.0
Math.floor(-99.1) = -100.0
Math.floor(99.9) = 99.0
Math.floor(-99.9) = -100.0


==============Math.ceil()==============
Math.ceil(99.1) = 100.0
Math.ceil(-99.1) = -99.0
Math.ceil(99.9) = 100.0
Math.ceil(-99.9) = -99.0