any subclass of an abstract class must either implement all of the abstract methods in the superclass or be iteself declared abstract why?
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Basically, an abstract class is a sort of template. In it, it says "any class that uses me will have the following functions, variables, etc.". Everything accessing a subclass of this will therefore assume, that these functions, variables, etc. exist - which will only be the case, if you implemented them.
Of course, you can have another abstract class, that has all stuff that that other one had plus something more - that would be ok without having to implement the functions, because it's still just a "template".
There is also something called an "Interface" , which solves similar problems. To read up on both Interfaces and abstract classes, I'd recommend this article.
Greetings,
Nepomuk
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