import java.util.*;

public class TopMap<K, V> extends TreeMap<Integer, V> {

   private final int maxElems;
   public TopMap(int maxNumberElements) {
      super(Collections.reverseOrder());
      maxElems = maxNumberElements;
      }
   @Override
   public V put(Integer key, V value) {
      //while (containsKey(key)) key = key + 1;  //optional hack
      if (size() < maxElems || key > lastKey())
         super.put(key, value);
      if (size() > maxElems)
         remove(lastKey());
      return value;
      }

   public static void main(String[] args) {
      TreeMap<Integer, String> islands = new TopMap<Integer, String>(3);
      islands.put( 507000, "Baffin");
      islands.put( 726000, "Borneo");
      islands.put(2131000, "Greenland");
      islands.put( 578000, "Madagascar");
      islands.put( 800000, "New Guinea");
      System.out.println("Three Largest Islands:");
      for (Map.Entry<Integer, String> island : islands.entrySet())
         System.out.println(island.getKey() + " sq km - " + island.getValue());
      }

   }