Usin Comprable Interface to compare strings

This is my goal.

I have 2 class’s
Person (authors)
Book (can have single or many authors. authors are stored in an Array of Person objects)

What i want to do is run the comparable interface to find out which book comes first based on the first author.

I have overwritten the method and it works with number data such as year, pages but I can not seem to get it to work with strings.

Anyone have any ideas?