Java - Math.random() method example

The Math.random() function returns floating-point, pseudo-random number between range [0,1), 0 (inclusive) and 1 (exclusive). Based on this function we are able to get a random number in range as we can see in the below examples.

Simple usage example:

public class MathExample {

    static double randomDouble(double min,double max) {
        return min + Math.floor((max - min) * Math.random());
    }

    static double randomFloat(float min, float max) {
        return min + (max - min) * Math.random();
    }

    public static void main(String[] args) {
        System.out.println( Math.random() ); // 0.9100486004606172
        System.out.println( Math.random() ); // 0.8630710741089413
        System.out.println( Math.random() ); // 0.8052253695967542

        System.out.println( randomDouble( 10, 20) ); // 12.0
        System.out.println( randomDouble(-10, 10) ); // -4.1

        System.out.println( randomFloat( 10, 20) ); // 14.514897223860018
        System.out.println( randomFloat(-10, 10) ); // -6.645075993092653
    }
}

1. Documentation

package java.lang;

public final class Math {

    public static double random() { ... }

}

2. Custom random method examples

2.1. Random double in range example

This example shows how to random numbers.

public class MathExample {

    static double randomizeDouble(double min, double max) {
        return min + (max - min) * Math.random();
    }

    public static void main(String[] args) {
        System.out.println(  randomizeDouble(-100.0, -10.0)); // -19.47848124694505
        System.out.println(  randomizeDouble( -8.0, 50.0  )); // 9.235851074094608
        System.out.println(  randomizeDouble(100.1, 1000.0)); // 292.6323795235495
    }
}

2.2 With nextDouble() method

import java.util.Random;

public class MathExample {

    static double randomizeDouble(double min, double max) {
        Random rand = new Random();

        return rand.nextDouble() * (max - min) + min;
    }

    public static void main(String[] args) {
        System.out.println(  randomizeDouble(-100.0, -10.0)); // -26.680584788543626
        System.out.println(  randomizeDouble( -8.0, 50.0  )); // 28.283331926707007
        System.out.println(  randomizeDouble(100.1, 1000.0)); // 464.69065618362106
    }
}

References

1. Random number generation - Wikipedia
2. Pseudorandom number generator - Wikipedia
3. List of random number generators - Wikipedia