Math class is mathematically related tools, which provide a lot of static methods, to complete the operation related to mathematical operations.
1.public static double abs (double num): to obtain absolute values. There are many overloaded.
2.public static double ceil (double num): rounding up.
3.public static double floor (double num): rounded down.
4.public static long round (double num): rounding.
Representative Math.PI approximate constant pi (double).