Generating Random Numbers

This lesson covers generating random numbers in Java using the Random class, so you can build logic with a random element, like a dice roll or rock-paper-scissors. It's for anyone searching "Java Random usage."

The Random class generates random numbers. Use it to build something like a dice-rolling or lottery program. The result changes every time you run it.

The example generates a dice roll from 1 to 6 with rnd.nextInt(6) + 1. Since nextInt(6) returns a number from 0 to 5, notice the + 1 adjusting it into the 1-to-6 range.

A common early mistake is misjudging nextInt()'s range. Not knowing that nextInt(n) returns a value from 0 up to (but not including) n can leave you confused when you don't get the range you expected.

In real projects, you can also specify a fixed seed value when you want the same sequence of random numbers to be reproducible — useful in a testing scenario.

📖 Reference code

import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random rnd = new Random();
        int dice = rnd.nextInt(6) + 1;
        System.out.println("Dice roll: " + dice);

        String[] choices = {"Rock", "Scissors", "Paper"};
        System.out.println("Rock-paper-scissors: " + choices[rnd.nextInt(choices.length)]);
    }
}

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🧪 This site can't compile or run Java directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).