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Java - Math.random() method example

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Created by:

daniell

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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:

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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

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Syntax	xxxxxxxxxx 1 package java.lang; 2 3 public final class Math { 4 5 public static double random() { ... } 6 7 } Note: Classes in the `java.lang` package are imported automatically, so it is not necessary to do it manually - we use just `Math.random()` call.
Parameters	This method does not take any arguments.
Result	double number value (primitive value).
Description	`random` is a static method that returns random float number from the range `<0, 1)` - inclusive 0 and exclusive 1.

2. Custom random method examples

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2.1. Random double in range example

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This example shows how to random numbers.

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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

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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
    }
}