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Not quite what I was saying but still somewhat correct.
Not everything is an Object in java, there are primitive data types like int, float, double, boolean, etc, and there are static methods which...

But how would the user do that? Do you want to have a GUI, do it via command line, read a text-document? Any part of a program which relies on interaction is more complicated by default.

What *is* a "decision tree'? You have to define the things you want to work with. How does the user interact with it, and how is anything altered? What kind of object is altered? How do you connect...

What exactly do you mean? What kind of code were you looking at?
Code usually does quite a lot, of course, what you define as "doing something" is the more important question.