Simple demonstration of HashMap

[Java Tip]

import java.util.HashMap;
import java.util.Map;
import java.util.Random;

class Counter {
  int i = 1;

  public String toString() {
    return Integer.toString(i);
  }
}

public class Statistics {
  private static Random rand = new Random();

  public static void main(String[] args) {
    Map hm = new HashMap();
    for (int i = 0; i < 10000; i++) {
      // Produce a number between 0 and 20:
      Integer r = new Integer(rand.nextInt(20));
      if (hm.containsKey(r))
        ((Counter) hm.get(r)).i++;
      else
        hm.put(r, new Counter());
    }
    System.out.println(hm);
  }
}