Math

The java.lang.Math is a final class and thus no class can extend this class. The constructor of the Math class is private and thus you cannot create an instance of the Math class.
＜Sample＞
double random_number = Math.random() * 10;
System.out.println(random_number);
System.out.println("abs = " + Math.abs(random_number));
System.out.println("ceil = " + Math.ceil(random_number));
System.out.println("floor = " + Math.floor(random_number));
System.out.println("round = " + Math.round(random_number));

A result varies every time.