TreeMap floorKey() method in java

import java.util.TreeMap;
public class TreeMapFloorkeyExample
{
   public static void main(String[] args)
   {
      TreeMap<Integer, String> tm = new TreeMap<Integer, String>();
      tm.put(60, "apple");
      tm.put(10, "banana");
      tm.put(50, "cherry");
      tm.put(30, "fig");
      tm.put(80, "grape");
      tm.put(90, "kiwifruit");
      // printing values of TreeMap
      System.out.println("TreeMap: " + tm);
      try
      {
         // passing null as parameter to floorKey() method
         System.out.println(tm.floorKey(null));
      }
      catch(Exception ex)
      {
         System.out.println("Exception: " + ex);
      }
   }
}