Question

So abstract classes can be extended, but so can any class right? So why are some specific classes abstract and others not?

Furthermore, I have tried to figure out but I always get rather confused but what is the actual difference between an interface and an abstract class?

Thanks to anyone who can clear this up for me!

Answer 1

An interface can only describe method signatures, eg

public void add(int a, int b);

And a class that implements it, must define the method.

An abstract class can only be inherited, but it can still define a method:

public void add(int a, int b) {
    return a+b;
}

And any classes that implement it can use that method. Abstract classes can also implement final methods, so they can never be re implemented by a class that extends it.