2D random walk, Java

Question

I'm writing a two-dimensional random walk that takes command line arguments. It's supposed to estimate how long it takes the random walker to hit the boundary of a 2N-by-2N square centered at the starting point.

What I got so far is:

public class RandomWalk 
{
    public static void main(String[] args) 
    {
        int N = Integer.parseInt(args[0]);
        int reps = Integer.parseInt(args[1]);
        int x = 0;       
        int y = 0;       
        double r;
        int steps = 0;

        while (x*x + y*y <= N*N) {
            steps++;
            r = Math.random();

            if      (r <= 0.25) x++;
            else if (r <= 0.50) x--;
            else if (r <= 0.75) y++;
            else if (r <= 1.00) y--;
        }

        System.out.println(steps);
   }

}

Just want to check if you guys think im doing it wrong.

Answer 1

Your program terminates only when the random walk reaches a treshold. Not the boundary of the area.

while (x*x + y*y <= N*N) {

An example: N = 100, x = 90, y = 90 ==> 90*90 + 90*90 = 16 200 > 10 000.

Switch it to:

while (x > -N && x < N && y > -N && y < N) {

This will be better. And your reps variable is newer used. Not even once, beside the setting it's value.What should be the purpose ot that?