java Math类

package cn.sasa.demo3;

import java.text.DecimalFormat;

public class MathDemo {
    public static void main(String[] args) {
        //返回平方根
        double sqrtNum = Math.sqrt(4);
        System.out.println(sqrtNum);
        
        //向下取整
        double floorNum = Math.floor(1.8);
        System.out.println(floorNum);
        
        //向上取整
        double ceilNum = Math.ceil(1.1);
        System.out.println(ceilNum);
        
        //四舍五入
        double roundNum = Math.round(4.5);
        System.out.println(roundNum);
        
        //绝对值
        double absNum = Math.abs(-7);
        System.out.println(absNum);
        
        //a的b次方
        double powNum = Math.pow(2, 3);
        System.out.println(powNum);
        
        //保留2位小数
        double d1 = 3.141592653;
//        DecimalFormat dformat = new DecimalFormat("#.##");
//        double dfNum = Double.parseDouble(dformat.format(d1));
        double dfNum = Double.parseDouble(String.format("%.2f", d1));
        System.out.println(dfNum);
        
    }
}