// A filter reads a source file of text, and filters and translates its 
// contents according to the specification given in the Jabtalk project handout.


interface Filter {

    // string of legal characters after the filtration process
    public static final String Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ ,.\n";



    // The filter must have a constructor as follows:
    //
    // Open the file with name `source' and prepare to begin reading and
    // filtering its contents.
    // Precondition: `source' is the name of a text file that does exist.
    // public Filter(String source);



    // Return true iff there is at least one more filtered char to come from 
    // my source file.
    public boolean hasMore();



    // Return the next filtered character from my source file.
    // Precondition: hasMore() is true.
    public char nextChar();

}