1. Math類

方法名

説明

public static int abs(int a)

獲取參數a的絕對值：

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)

獲取a的b次冪

public static long round(double a)

四捨五入取整 

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次冪：" + Math.pow(2, 8));//256.0
        System.out.println("四捨五入 = "+Math.round(12.1)); //12
        System.out.println("四捨五入 = "+Math.round(12.8)); //13
        System.out.println(Math.random());   //[0.0 , 1.0)
        System.out.println((int)(Math.random()*10+1));  //[1,11)

常用類總結2 - 指南_Math

2. System類

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