1. import java.util.*;2. class KeyMaster {3. public int i;4. public KeyMaster(int i) { this.i = i; }5. public boolean equals(Object o) { return i == ((KeyMaster)o).i; }6. public int hashCode() { return i; }7. }8. public class MapIt {9. public static void main(String[] args) {10. Set < KeyMaster > set = new HashSet < KeyMaster > ();11. KeyMaster k1 = new KeyMaster(1);12. KeyMaster k2 = new KeyMaster(2);13. set.add(k1); set.add(k1);14. set.add(k2); set.add(k2);15. System.out.print(set.size() + “:”);16. k2.i = 1;17. System.out.print(set.size() + “:”);18. set.remove(k1);19. System.out.print(set.size() + “:”);20. set.remove(k2);21. System.out.print(set.size());22. }23. }