java.util.Random

By / 26 May 2025 / 2 minutes of reading

The Random class is part of the java.util package and is used to generate pseudo-random numbers of different types: int, long, float, double, boolean, and Gaussian values.

  • Based on a 48-bit seed using a linear congruential formula.
  • Thread-safe only if externally synchronized.
  • Can generate both bounded and unbounded values.

Commonly Used Methods

Simple Program: Lottery Generator

import java.util.Random;

public class SimpleRandomDemo {
    public static void main(String[] args) {
        Random random = new Random();
        System.out.println("Your lucky lottery numbers are:");

        for (int i = 0; i < 5; i++) {
            int number = random.nextInt(100); // 0 to 99
            System.out.println("Number " + (i + 1) + ": " + number);
        }
    }
}

Problem Statement(Non-repeating Random Question Generator):

LotusJavaPrince is designing a quiz app that generates random question indices for each user. He wants to ensure that no question is repeated during a session. Use java.util.Random to generate non-repeating random indices from a list of questions.

import java.util.Random;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class QuizApp {
    public static void main(String[] args) {
        // Sample questions
        String[] questions = {
            "What is Java?",
            "Explain polymorphism.",
            "What is inheritance?",
            "Define encapsulation.",
            "What is abstraction?",
            "What are exceptions in Java?",
            "Difference between ArrayList and LinkedList?",
            "Explain JVM, JRE, and JDK.",
            "What is a constructor?",
            "What is an interface?"
        };

        // Shuffle indices for random order without repetition
        List<Integer> indices = new ArrayList<>();
        for (int i = 0; i < questions.length; i++) {
            indices.add(i);
        }

        // LotusJavaPrince wants randomness
        Collections.shuffle(indices, new Random());

        // Mahesh ensures no repetition
        System.out.println("Randomized Question Set for the Session:");
        for (int index : indices) {
            System.out.println("- " + questions[index]);
        }
    }
}

java.util.Random is ideal for basic random number generation.

  • Use nextInt(bound) for bounded numbers and nextGaussian() for statistical simulations.
  • For non-repeating sequences, combine Random with structures like List and Collections.shuffle().
  • For cryptographic security, use java.security.SecureRandom instead.

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