RosettaCodeData/Task/Knuths-algorithm-S/Java/knuths-algorithm-s-1.java

import java.util.*;

class SOfN<T> {
    private static final Random rand = new Random();

    private List<T> sample;
    private int i = 0;
    private int n;

    public SOfN(int _n) {
        n = _n;
        sample = new ArrayList<T>(n);
    }

    public List<T> process(T item) {
        if (++i <= n) {
            sample.add(item);
        } else if (rand.nextInt(i) < n) {
            sample.set(rand.nextInt(n), item);
        }
        return sample;
    }
}

public class AlgorithmS {
    public static void main(String[] args) {
        int[] bin = new int[10];
        for (int trial = 0; trial < 100000; trial++) {
            SOfN<Integer> s_of_n = new SOfN<Integer>(3);
            for (int i = 0; i < 9; i++) s_of_n.process(i);
            for (int s : s_of_n.process(9)) bin[s]++;
        }
        System.out.println(Arrays.toString(bin));
    }
}