On the other hand, a couple of IDEs have a concept of a "main class"
(Eclipse is one of them), and that concept basically refers to which class's
main method the IDE should run when you tell it to run the application. Note
that every "run configuration" (that's the term Eclipse uses) has exactly
one main class, but a given project may have multiple main classes (which
implies multiple "run configurations" can be associated with a single
project).

   So as Lew said, if it's your application, then you, as the designer,
just choose a class to be your main class. If you're inheriting code from
someone else, then you just gotta search for static void methods called
"main" which take an array of String as an argument (different IDEs have
different ways of searching through the code base). If you gotta do this
programmatically, then you iterate through all the candidate classes, using
reflection to check for the existence of such a method.

   - Oliver

thanks LEW