Math.random () and random.nextint () differences

Package cn.wangbingan.vip;import java.util.random;/** * math.random () and random.nextint () differences  *  *  @author  ak *  */public class randomtest {public  static void main (String[] args)  {// TODO Auto-generated method  stub//  Random Number Object Random random = new random ();//  start time long starttime1 =  system.nanotime ();//  generate random number Long a = random.nextint (10000);//  end time long  Endtime1 = system.nanotime ();//  time consuming long time1 = endtime1 - starttime1 ; System.out.println ("Generate random Number:"  + a +  "=>random Time:"  + time1);//  start time long  starttime2 = system.nanotime ();//  generate random number int b =  (int)   (Math.random ()  * 10000);//  End Time Long endtime2 = system.nanotime ();//  time consuming long time2  = endtime2 - starttime2; System.out.println ("Generate random Number:"  + b +  "=>math Time:"  + time2);}}

Output Result:

Generate random Number: 9441=>random time: 11000

Generate random Number: 7109=>math time: 43000

The former generates a random number that is more efficient than the latter, which is about 50% to 80% of the time, possibly higher.

This is caused by the following reasons:

Math.random () is an internal method of random.nextdouble (). (So I'm sure Dad's more efficient than his son.)

Random.nextdouble () uses Random.next () two times, with a uniform distribution range of 0 to 1-(2 ^-53).

Random.nextint (n) uses Random.next () no more than two times, and returns a distribution with a range of 0 to N-1

Math.random () and random.nextint () differences