//public static int abs ( int a)取绝对值
//public static double ceil ( double a)向上取整
//public static double floor ( double a)向下取整
//public static int max ( int a, int b)获取最大值
//public static int min ( int a, int b)获取最小值
//public static double pow ( double a, double b)获取a的b次幂
//public static double random () 获取随机数 返回带正号的 double 值,该值大于等于 0.0 且小于 1.0。
//public static int round ( float a)四舍五入
//public static double sqrt ( double a)获取正平方根
//public BigDecimal add (BigDecimal augend)//加
//public BigDecimal subtract (BigDecimal subtrahend)//减
//public BigDecimal multiply (BigDecimal multiplicand)//乘
//public BigDecimal divide (BigDecimal divisor)//除法
//public BigDecimal divide (BigDecimal divisor,int scale, int roundingMode)//scale 小数点后面保留几位