Method main

collections/Statistics.java:9–19

(String[] args)

public class Statistics {
  public static void main(String[] args) {
    Random rand = new Random(47);
    Map<Integer, Integer> m = new HashMap<>();
    for(int i = 0; i < 10000; i++) {
      // Produce a number between 0 and 20:
      int r = rand.nextInt(20);
      Integer freq = m.get(r);               // [1]
      m.put(r, freq == null ? 1 : freq + 1);
    }
    System.out.println(m);
  }
}
/* Output:
{0=481, 1=502, 2=489, 3=508, 4=481, 5=503, 6=519,