Java read text files and store the value in a 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)throws Exception{
        FilenameFilter ff = new OnlyExt("txt");
        File folder = new File("c:/");
        File[] files = folder.listFiles(ff);
        Map<String,String> map=new LinkedHashMap<String,String>();
        for(int i=0;i<files.length;i++){
        FileReader fr = new FileReader(files[i].getPath());
            BufferedReader reader = new BufferedReader(fr);
            String st = "",str=" ";
            while((st = reader.readLine()) != null) {
        str+=st;
        }
        map.put(files[i].getName(),str);
        }
        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());
    }
  }
}

thanks for the answer... i am having 10 records in each file and i have 4 files. all 10 records from file 1 are inserted at first index. it behaves similarly for all. can you suggest me another option?