Java - how much logic to put in the main class?

Question

How much logic do you normally put in the main class? Should logic in the main class be at minimum, only instantiating other, specialized classes, and running all the tasks from

Answer 1

Should logic in the main class be at minimum, only instantiating other, specialized classes, and running all the tasks from there?

Yes. main method and its surrounding class should ideally be used only as an entry point to start the program. The mere existence of the surrounding class is just an artifact of the way Java programs are composed (everything must be inside some class), and there's no reason why it should contain other stuff in addition to the main method (but there definitely are reasons why it shouldn't).

When you get the interesting classes (those that form the actual program) separated, you open doors for all kinds of flexibility. Perhaps some of those classes could be used in some other projects. Perhaps some day you'll want to replace some of them with better implementations. Maybe you'll find a better order to instantiate all those classes - so just swap a few lines. Or how about executing lengthy startup loadings and instantiations in parallel threads? Just wrap some of them to suitable Executors. Good luck trying this with a 1000+ line main class.

This kind of flexibility matters for everything except maybe for 100-line elementary examples, prototypes and such. But given that even small tools tend to grow, why not do it correctly right from the beginning?