That's really going to depend on what you mean by "Create a class in empty method().java"
All we get from that is that you are probably using the Java language (but that could be Javascript - some do confuse the two), that you want to create a class, and that you have an empty method.
So I'm going to have to guess that you are talking about
Java - Inner classes[
^]
If you aren't, then you really need to start by reading this:
Asking questions is a skill[
^] and think about what you need to know and what you need to tell us in order to get help.