常用类总结2 - 指南

1. Math类

方法名	说明
public static int abs(int a)	获取参数a的绝对值：
public static double ceil(double a)	向上取整
public static double floor(double a)	向下取整
public static double pow(double a, double b)	获取a的b次幂
public static long round(double a)	四舍五入取整

        System.out.println("向上取整："+Math.ceil(13.4));   //14.0
        System.out.println("向上取整："+Math.ceil(-11.8));  //-11.0
        System.out.println("向下取整："+Math.floor(15.9));  //15.0
        System.out.println("向下取整："+Math.floor(-12.6)); //-13.0
        System.out.println("2的8次幂：" + Math.pow(2, 8));//256.0
        System.out.println("四舍五入 = "+Math.round(12.1)); //12
        System.out.println("四舍五入 = "+Math.round(12.8)); //13
        System.out.println(Math.random());   //[0.0 , 1.0)
        System.out.println((int)(Math.random()*10+1));  //[1,11)

2. System类

常用API方法：
public static native long currentTimeMillis();
public static native void arraycopy(Object src,  int  srcPos, Object dest, int destPos, int length);
public static void exit(int status)
public static void setOut(Prin