Probability in Java

Question

I was curious to know, how do I implement probability in Java? For example, if the chances of a variable showing is 1/25, then how would I implement that? Or any other probability? Please point me in the general direction.

Answer 1

You'd use Random to generate a random number, then test it against a literal to match the probability you're trying to achieve.

So given:

boolean val = new Random().nextInt(25)==0; 

val will have a 1/25 probability of being true (since nextInt() has an even probability of returning any number starting at 0 and up to, but not including, 25.)

You would of course have to import java.util.Random; as well.

As pointed out below, if you're getting more than one random number it'd be more efficient to reuse the Random object rather than recreating it all the time:

Random rand = new Random(); boolean val = rand.nextInt(25)==0; 

..

boolean val2 = rand.nextInt(25)==0; 

Answer 2

Generally you use a random number generator. Most of those return a number in the interval [0,1] so you would then check whether that number is <= 0.04 or not.

if( new Random().nextDouble() <= 0.04 ) {  //you might want to cache the Random instance    //we hit the 1/25 ( 4% ) case. } 

Or

if( Math.random() <= 0.04 ) {   //we hit the 1/25 ( 4% ) case. } 

Note that there are multiple random number generators that have different properties, but for simple applications the Random class should be sufficient.