Why Can You Instantiate a Class within its Definition?

Question

A coworker (who is very new to Java) stopped in today and asked what seemed like a very simple question. Unfortunately, I did an absolutely horrible job of trying to explain

Answer 1

The same reason you can call a method on line 42 that isn't defined until line 78? Java isn't a scripting language, so things don't have to be declared before they are used (this is even true of some scripting languages, actually). Class definitions are considered as a whole at compile time.

You can even instantiate an object of a class in its own constructor:

public class Test {
    Test a;

    Test() {
        a = new Test();
    }

    public static void main(String[] args) {
        System.out.println(new Test());
    }
}

This produces... wait for it... a java.lang.StackOverflowError.