Error handling

Hi folks,
im currently writing a game, and as the project gets bigger im slowly noticing that good error handling will be essential in the long run.
I read through Javatutorials etc about error handling but i don’t really understand parts of it.
When a nullpointerexception happens why does the methode not need a throws nullpointerexception?
How can it be that the errormessage with a nullpointerexception looks different in a jme3 game if it is integrated in a Swing interface than if it is not?
How can i open the same Window it displays the exceptions in from a try-catch block?
Thanks for any help

A lot of this is basic java stuff (i.e. a NPE is a runtime exception so hence does not need to be declared as thrown)…