Java Random Number Generator — How to Generate Integers With Math Random
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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 4
public 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 #1
doubleRandomNumber = 2.431392914284627
randomNumber = 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…