example code TreeMap comparator

package myutil;

import java.util.Comparator;
import java.util.TreeMap;
    class Mycompare implements Comparator
    {
        public int compare(Object o1,Object o2)
        {
            Integer i1=(Integer)o1;
            Integer i2=(Integer)o2;
            return -i1.compareTo(i2);
        }
    }

public class TreeMapCom {
    public static void main(String[] args) 
    {
        TreeMap map=new TreeMap(new Mycompare());
    map.put(new Integer(100),"orange");
    map.put(new Integer(300),"apple");
    map.put(new Integer(200),"grapes");
    map.put(new Integer(400),"grapes");
    System.out.println("The TreeeMap Is "+map);
//    Try to place the null you will get NullPointerException
    //map.put(null,"javasun");
      }
}

output:
The TreeeMap Is {400=grapes, 300=apple, 200=grapes, 100=orange}