import java.util.*;

public class TopMultiMap<K, V> extends TreeMap<Integer, V> {
   private final int maxElems;
   private int minKey = Integer.MIN_VALUE + 1;
   private static Comparator<Integer> topComp = new Comparator<Integer>() {
      public int compare(Integer a, Integer b) { return a < b ? 1 : -1; } };
   public TopMultiMap(int maxNumberElements) {
      super(topComp);
      maxElems = maxNumberElements;
      }
   @Override
   public V put(Integer key, V value) {
      if (key >= minKey) {
         super.put(key, value);
         int elemNum = 0;
         if (size() >= maxElems)
            for (Map.Entry<Integer, V> entry : super.entrySet())
               if (elemNum++ < maxElems) minKey = entry.getKey();
         }
      return value;
      }
   @Override
   public Set<Map.Entry<Integer, V>> entrySet() {
      return headMap(minKey - 1).entrySet();
      }

   public static void main(String[] args) {
      TreeMap<Integer, String> islands = new TopMultiMap<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());
      }

   }