Java tutorial
import java.util.HashMap; import java.util.Map; class Counter { int i = 1; public String toString() { return Integer.toString(i); } } public class Main { public static void main(String[] args) { Map hm = new HashMap(); for (int i = 0; i < 10; i++) { Integer r = new Integer(20); if (hm.containsKey(r)) ((Counter) hm.get(r)).i++; else hm.put(r, new Counter()); } System.out.println(hm); } }