Random number with Probabilities

Question

I am wondering what would be the best way (e.g. in Java) to generate random numbers within a particular range where each number has a certain probability to occur or not?

Answer 1

You already wrote the implementation in your question. ;)

final int ran = myRandom.nextInt(100);
if (ran > 50) { return 3; }
else if (ran > 20) { return 2; } 
else { return 1; }

You can speed this up for more complex implementations by per-calculating the result on a switch table like this:

t[0] = 1; t[1] = 1; // ... one for each possible result
return t[ran];

But this should only be used if this is a performance bottleneck and called several hundred times per second.