Jakarta Commons Cookbook

8.4. Generating Random Variables

Problem

J2SE 1.4 includes a java.lang.Math class that provides a mechanism to get a random double value between 0.0 and 1.0, but you need to create random boolean values, or random int variables between zero and a specified number.

Solution

Generate random variables with Commons Lang RandomUtils, which provides a mechanism to generate random int, long, float, double, and boolean variables. The following code generates a random integer between zero and the value specified in the parameter to nextInt( ) :

import org.apache.commons.lang.math.RandomUtils;

// Create a random integer between 0 and 30
int maxVal = 30;
int randomInt = RandomUtils.nextInt( maxVal );

Or, if your application needs a random boolean variable, create one with a call to the static method nextBoolean( ):

import org.apache.commons.lang.math.RandomUtils;
 
boolean randomBool = RandomUtils.nextBoolean( );

Discussion

A frequent argument for not using a utility like RandomUtils is that the same task can be achieved with only one line of code. For example, if you need to retrieve a random integer between 0 and 32, you could write the following code:

int randomInt = (int) Math.floor( (Math.random( ) * (double) maxVal) );

While this statement may seem straightforward, it does contain a conceptual complexity not present in RandomUtils.nextInt(maxVal). RandomUtils.nextInt(maxVal) is a simple statement: “I need a random integer between 0 and maxVal“; the statement without RandomUtils is ...