You can write the playlist into a file but if you want to read the file after, you should use the playlist as an object and serialize it. The writing procedure should look something like this:
FileOutputStream f = new FileOutputStream("tmp");
ObjectOutput s = new ObjectOutputStream(f);
s.writeObject("Today");
s.writeObject(new Date());
s.flush();
And the reading procedure should look something like this:
FileInputStream in = new FileInputStream("tmp");
ObjectInputStream s = new ObjectInputStream(in);
String today = (String)s.readObject();
Date date = (Date)s.readObject();