How to generate random numbers in Java

In this tutorial, we are going to see how to generate a random number using Java’s Random class and the Math.Random method.

Generate a random number using Java

Java provides interesting ways to generate random numbers, not only for scientific calculations but also for other applications, such as creating a unique session ID on a web server, cryptography, security, math, etc.

There are two ways to do this:

  • Use of the Random class (in the java.util package).
  • Using the Math.Random java class (however, this will generate a double between 0.0 and 1.0).

Example: using the Random class

Suppose we need to generate 10 random numbers between 0 and 100.

import java.util.Random;

public class RandomNbr{
    public static void main(String[] args) {
         Random obj = new Random();
         for (int i = 0; i < 10; i++){
             int nbr = obj.nextInt(100);
             System.out.println("Random number : " + nbr); 

An object of the Random class is initialized as “obj”. The Random class has the “nextInt” method. This will provide a random number based on the argument specified as the upper limit, while the lower limit is set to 0. This will result in 10 random numbers displayed.

Example: using Math.Random

The Math class contains several methods for performing various numerical operations, such as calculating the exponential, logarithms, etc. One of these methods is random(). This method returns a double value greater than or equal to 0.0 and less than 1.0. The returned values are chosen in a pseudo-random manner. This method can only generate random numbers of type Doubles. The following program explains how to use this method:

public class RandomNbr{
     public static void main(String[] args) {
          for(int i = 0; i < 10; i++){



The java.util.Random class implements what is generally called a linear congruence generator (GCL). It is designed to be fast but does not meet the requirements of real-time use. For example, use in scientific calculations, cryptography, etc.

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