Java Storing Id and File Name in Map

import java.io.*;
import java.util.*;
class OnlyExt implements FilenameFilter{
  String ext;
  public OnlyExt(String ext){
  this.ext="." + ext;
  }
  public boolean accept(File dir,String name){
  return name.endsWith(ext);
  }
}
class MapExample
{
    public static void main(String[] args) 
    {
        FilenameFilter ff = new OnlyExt("txt");
        File folder = new File("c:/");
        File[] files = folder.listFiles(ff);
        Map<Integer,String> map=new HashMap<Integer,String>();
        for(int i=0;i<files.length;i++){
        int j=i+1;
        map.put(j,files[i].getName());
        }
        Set set = map.entrySet();
        Iterator i = set.iterator();

        while(i.hasNext()){
        Map.Entry me = (Map.Entry)i.next();
        System.out.println(me.getKey() + " \t:\t " + me.getValue());
    }
    }
}

hey many thanks.....