Math

   		//Math.abs(double num);获取绝对值
        System.out.println(Math.abs(-2.6));//2.6
        
        //Math.ceil(double num);向上取整
        System.out.println(Math.ceil(2.1));//3.0
        
        //Math.floor(double num);向下取整
        System.out.println(Math.floor(2.9));//2.0
        
        //Math.round(double num);四舍五入
        System.out.println(Math.round(2.6));//3