[morsch]

Well, obviously, by using them in the language without requiring them on the filesystem? I think you should be able to cat together all the .java files in your project and it should still compile. I guess you could easily do it using a very simple preprocessor.

[felipemnoa]

If you do that you will no longer be able to tell the overall structure of your project at a single glance without using an IDE like Eclipse. Adding and removing packages becomes harder without the IDE. What are the upsides? You've increased the complexity for no good reason.

[morsch]

Easier rapid prototyping and exploratory programming. Edit all the classes of your small/exploratory project in a single file. If the project expands, it should be an automated refactoring to move classes to their own files.

I do this all the time using static inner classes.