How to Generate Random Integers in Java

Generating random numbers using Java is one of the most common question beginners tend to fall upon. However, the task is not at all difficult. Let us look at the three common approaches which are being followed in order to generate a Random Integer.

java.util.Random
Math.random
java.util.concurrent.ThreadLocalRandom

java.util.Random

In order to generate random integers using this class, we need to create an instance of the class first and then invoke methods such as nextInt(), nextDouble(), etc.
We can generate random numbers of type integers, float, double, long, Boolean using this class. Let us look at an example to know how that works.

// A Java program to demonstrate random number generation // using java.util.Random; import java.util.Random; public class RandomIntegers { public static void main(String args[]) { // create instance of Random class Random rand = new Random(); // Generate random integers int rand_int1 = rand.nextInt(); // Print random integers System.out.println("Random Integers: " + rand_int1); } }

Output

Let us look at the output of the above example code.

Random Integer using Random Class — Fig.1- Generating Random Number using *java.util.Random*

Math.random()

The math class contains numerous methods for performing various numeric operations such as calculating exponential values, logarithms, etc. One of these methods is random(), which returns a double value in the range of 0.0 to 1.0. But this method can generate random values of type double only.
Let us look at an example to demonstrate how Math.random() is used to generate random value.

// Java program to demonstrate working of // Math.random() to generate random numbers public class RandomIntegers { public static void main(String args[]) { // Generating random doubles System.out.println("Random doubles: " + Math.random()); } }

Output

Let us look at the output of the above example code.

Random Integer using Random Method — Fig.2- Generating Random Number using *Math.random*

java.util.concurrent.ThreadLocalRandom

This class was introduced way back in Java 1.7 version to generate random numbers of type integer, double, Boolean, etc. Let us look at an example code to generate random numbers of type integers, double and Boolean.

// Java program to demonstrate working of ThreadLocalRandom // to generate random numbers. import java.util.concurrent.ThreadLocalRandom; public class RandomIntegers { public static void main(String args[]) { // Generate random integers int rand_int1 = ThreadLocalRandom.current().nextInt(); // Print random integers System.out.println("Random Integers: " + rand_int1); // Generate Random doubles double rand_dub1 = ThreadLocalRandom.current().nextDouble(); // Print random doubles System.out.println("Random Doubles: " + rand_dub1); // Generate random booleans boolean rand_bool1 = ThreadLocalRandom.current().nextBoolean(); // Print random Booleans System.out.println("Random Booleans: " + rand_bool1); } }

Output

Let us look at the output of the above example code.

Random Integer using ThreadLocalRandom Class — Fig.3- Generating Random Number using *java.util.concurrent.ThreadLocalRandom*

Generate Random Number within a Range

In a scenario where the random number being generated is restricted to a certain range we use the following technique.

//Generating Random number //within a given range import java.util.Random; public class RandomIntegers { public static void main(String args[]) { Random rand = new Random(); // Obtain a number between [0 - 49]. int n = rand.nextInt(50); System.out.println("Random Number: " + n); } }

Output

Let us look at the output of the above example code.

Random Integer within-a Range — Fig.4- Generating Random Number within a Range

Here, the number generated will always be in between 0 - 49. Basically, we just need to pass the upper limit of the range as the parameter and it will generate a random number between 0 to upper limit – 1.

Summary

Having discussed so many methods and different scenarios of random number generation, now you can manipulate and generate a random number as per your requirement.

How to Generate Random Integers in Java

java.util.Random

Output

Math.random()

Output

java.util.concurrent.ThreadLocalRandom

Output

Generate Random Number within a Range

Output

Summary

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Author : Satyam Kumar -

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