How to Generate Random Numbers in Java

In this tutorial, we will learn how to generate random number in Java-

• Using Java Random Class
• Using Java Math.Random

Let's look at how to generate 10 random numbers in Java -

Example: Using Java Random Class

First, we will see the implementation using java.util.Random - Assume we need to generate 10 digit random number in Java between 0 to 100.

import java.util.Random;
public class RandomNumbers{
        public static void main(String[] args) {
        	Random objGenerator = new Random();
            for (int iCount = 0; iCount< 10; iCount++){
              int randomNumber = objGenerator.nextInt(100);
              System.out.println("Random No : " + randomNumber); 
             }
     }
}

Output:

Random No : 17
Random No : 57
Random No : 73
Random No : 48
Random No : 68
Random No : 86
Random No : 34
Random No : 97
Random No : 73            
Random No : 18   

An object of Random class is initialized as objGenerator. The random number generator in Java class has a method as nextInt. This will provide a random number based on the argument specified as the upper limit, whereas it takes lower limit is 0.Thus, we get 10 random numbers displayed.

Example: Using Java Math.Random

Now, if we want 10 random numbers generated java but in the range of 0.0 to 1.0, then we should make use of random number generator Java class called math.random() .

You can use the following loop to generate them-

public class DemoRandom{
  public static void main(String[] args) {
    for(int xCount = 0; xCount< 10; xCount++){
      System.out.println(Math.random());
    }
  }
}

Output:

0.46518450373334297
0.14859851177803485
0.5628391820492477
0.6323378498048606
0.1740198445692248
0.9140544122258946
0.9167350036262347
0.49251219841030147
0.7426056725722353 

Now, you know how those strange numbers are generated!!!

Summary:

Random number can be generated using two ways. You can use Random Java class (in package java.util) or Using Math.random Java class (however this will generate double in the range of 0.0 to 1.0 and not integers).