Random Numbers

If you are a software developer, you may have come across the requirement of generating random numbers in your application. While developing any kind of applications, you often need to generate random numbers. In Java, it is easy to generate random numbers using some in-built methods and classes. In this article, we will see three different ways to generate random numbers in java. Let’s start with the definition of random numbers.

What Is Random Number?

“Randomness” is something which is totally unpredictable and unbiased. Random number is a number picked randomly from the given set of numbers. There will be no relation or dependency between the two successively picked numbers.

Random Number Generator :

An ideal Random Number Generator is the one which generates a series of numbers in the given range where,

Each possible number have equal probability of picking up.
There will be no relation or dependency between the previously generated number and the present one.
How To Generate Random Numbers In Java?

Java provides two ways to generate random numbers. One is using java.util.Random class and another one is using Math.random() method. There is one more method introduced in JAVA 7. It is using ThreadLocalRandom class. We will discuss all three methods in this article.

Generating Random Numbers Using java.util.Random Class :

Using java.util.Random class, you can generate random integers, doubles, floats, longs and booleans. Below is the program which generates random integers, doubles and booleans using java.util.Random class.

Output :

Random Integers : 238886529

Random Integers : 1463682739

Random Integers : -1247541726

Random Integers : 34314299

Random Integers : 1658793122

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Random Doubles : 0.7443798462870127

Random Doubles : 0.8382139571324086

Random Doubles : 0.9680505961503302

Random Doubles : 0.5623901155047567

Random Doubles : 0.37285000690287773

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Random booleans : false

Random booleans : true

Random booleans : false

Random booleans : false

Random booleans : false

Note : Integers generated are in the range of -231 and 231-1. Generated doubles are in the range from 0.0 to 1.0.

Generating Random Numbers Using Math.random() :

Output :

Random Doubles : 0.7783847001873636

Random Doubles : 0.3895881606319488

Random Doubles : 0.4798586710671108

Random Doubles : 0.6203717760219122

Random Doubles : 0.7460629328768049

Generating Random Numbers Using ThreadLocalRandom Class :

java.util.concurrent.ThreadLocalRandom class is introduced in Java 7. Below program shows how to generate random integers, doubles and booleans using ThreadLocalRandom class.

Output :

Random Integers : -1626309835

Random Integers : 332111237

Random Integers : -1585909207

Random Integers : 1070972416

Random Integers : -1874591696

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Random Doubles : 0.7840295282815645

Random Doubles : 0.36849802111866514

Random Doubles : 0.6551894273753474

Random Doubles : 0.5993075213578543

Random Doubles : 0.7289343843664791

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Random booleans : true

Random booleans : false

Random booleans : false

Random booleans : true

Random booleans : true

Generating Random Numbers In The Given Range :

Below is the java program which generates random integers in the range from 0 to 50 using all three methods – Random class, Math.random() and ThreadLocalRandom class.

Output : 

Random integers between 0 and 50 using Random class : 16 12 30 26 17 

Random integers between 0 and 50 using Math.random() : 12 43 42 32 45 

Random integers between 0 and 50 using ThreadLocalRandom 12 40 16 17 3