# Java Random Number Generator — How to Generate Integers With Math Random

Computer-generated random numbers are divided into two categories: true random numbers and pseudo-random numbers.

True random numbers are generated based on external factors. For example, generating randomness using surrounding noises.

But generating such true random number is a time-consuming task. Therefore, we can utilize pseudo-random numbers which are generated using an algorithm and a seed value.

These pseudo-random numbers are sufficient for most purposes. For example, you can use them in cryptography, in building games such as dice or cards, and in generating OTP (one-time-password) numbers.

In this article, we will learn how to generate pseudo-random numbers using `Math.random()` in Java.

# 1. Use Math.random() to Generate Integers

`Math.random()` returns a double type pseudo-random number, greater than or equal to zero and less than one.

Let’s try it out with some code:

`public static void main(String[] args) {  double randomNumber = Math.random();  System.out.println(randomNumber);}// output #1 = 0.5600740702032417// output #2 = 0.04906751303932033`

`randomNumber` will give us a different random number for each execution.

Let’s say we want to generate random numbers within a specified range, for example, zero to four.

`// generate random numbers between 0 to 4public static void main(String[] args) {  // Math.random() generates random number from 0.0 to 0.999  // Hence, Math.random()*5 will be from 0.0 to 4.999  double doubleRandomNumber = Math.random() * 5;  System.out.println("doubleRandomNumber = " + doubleRandomNumber);  // cast the double to whole number  int randomNumber = (int)doubleRandomNumber;  System.out.println("randomNumber = " + randomNumber);}/* Output #1doubleRandomNumber = 2.431392914284627randomNumber = 2*/`

When we cast a double to int, the int value keeps only whole number part.

For example, in the above code, `doubleRandomNumber` is `2.431392914284627` . `doubleRandomNumber`'s whole number part is `2` and fractional part (numbers after the…