Java: do something x percent of the time

Question

I need a few lines of Java code that run a command x percent of the time at random.

psuedocode:

boolean x = true 10% of cases.

if(x){
  System.out.println("you got lucky");
}

Answer 1

You just need something like this:

Random rand = new Random();  if (rand.nextInt(10) == 0) {     System.out.println("you got lucky"); } 

Here's a full example that measures it:

import java.util.Random;  public class Rand10 {     public static void main(String[] args) {         Random rand = new Random();         int lucky = 0;         for (int i = 0; i < 1000000; i++) {             if (rand.nextInt(10) == 0) {                 lucky++;             }         }         System.out.println(lucky); // you'll get a number close to 100000     } } 

If you want something like 34% you could use rand.nextInt(100) < 34.

Answer 2

If by time you mean times that the code is being executed, so that you want something, inside a code block, that is executed 10% of the times the whole block is executed you can just do something like:

Random r = new Random();

...
void yourFunction()
{
  float chance = r.nextFloat();

  if (chance <= 0.10f)
    doSomethingLucky();
}

Of course 0.10f stands for 10% but you can adjust it. Like every PRNG algorithm this works by average usage. You won't get near to 10% unless yourFunction() is called a reasonable amount of times.

Answer 3

To take your code as a base, you could simply do it like that:

if(Math.random() < 0.1){
  System.out.println("you got lucky");
}

FYI Math.random() uses a static instance of Random