Transfer Lowercase Letters Not Convert

I am trying to sort out all lower case letters out of my text file into a new file. I am not very good with char values. My text file that is being read says

AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz.

I just need it to write out all the lower case. The code below is what I have to read and write the file.

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintStream;
import java.util.Scanner;
public class Lower {
Scanner in=new Scanner(System.in);
FileWriter filw;
String fr;

[Code] .....