The java.lang.Math.random() method returns random number between 0.0 and 1.0 including 0.0 but not including 1.0. By multiplying Math.random() result with a number, for example 10 will give us a range of random number between 0.0 and 10.0.

To get a random number between two numbers (n and m) we can use the formula of: n + (Math.random() * (m - n)). Where n is the lowest number (inclusive) and m is the highest number (exclusive).

package org.kodejava.lang;

public class RandomNumberExample {
    public static void main(String[] args) {
        // The Math.random() returns a random number between 0.0 and 1.0 
        // including 0.0 but not including 1.0.
        double number = Math.random();
        System.out.println("Generated number: " + number);

        // By multiplying Math.random() result with a number will give
        // us a range of random number between, for instance 0.0 to 10.0 as
        // shown in the example below.
        number = Math.random() * 10;
        System.out.println("Generated number: " + number);

        // To get a random number between n and m we can use the formula:
        // n + (Math.random() * (m - n)). The example below creates random
        // number between 100.0 and 200.0.
        int n = 100;
        int m = 200;
        number = n + (Math.random() * (m - n));
        System.out.println("Generated number: " + number);

        // Creates an integer random number
        int random = 100 + (int) (Math.random() * 100);
        System.out.println("Generated number: " + random);
    }
}

Here is an example result of our program.

Generated number: 0.024974902600698234
Generated number: 2.271051510086771
Generated number: 147.542543014888
Generated number: 112