How to Generate Random Integers (and Doubles) Within a Specific Range in Java?

Math.random() Manipulation: Generating Random Integers Within a Specified Range

The Java function Math.random() generates random numbers within the range [0, 1). However, there are situations where you may need to obtain random integers within a specific range. This article demonstrates how to achieve this using Math.random().

Intention to Generate a Random Integer Between Three and Five

While the statement "(int) Math.random() * 5 3" does not correctly generate random integers within the range [3, 5], it can be corrected using a custom method:

int randomWithRange(int min, int max) {
    int range = (max - min) + 1;
    return (int) (Math.random() * range) + min;
}

This method calculates the range of possible values, multiplies it by Math.random(), and adds the minimum value to ensure inclusivity.

Output Example

System.out.println(randomWithRange(3, 5));
// Output: 3

Idiot-Proofing for Incorrect Ordering

To prevent errors if min is greater than max, an updated method is:

int randomWithRange(int min, int max) {
    int range = Math.abs(max - min) + 1;
    return (int) (Math.random() * range) + (min <= max ? min : max);
}

Extensions for Double Random Number Generation

A similar method can be used to generate random double-precision numbers:

double randomWithRange(double min, double max) {
    double range = (max - min);
    return (Math.random() * range) + min;
}

Using this method:

System.out.println(randomWithRange(3.0, 5.0));

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