Can I assume that the class doesn't care how many times a method signature is duplicated in multiple interfaces?
The class just has to make sure that it implements the method regardless of how many times the method signature is listed in different interfaces?
Likewise does the same apply when a subclass extends a parent class that has a method that is also mentioned in an interface...
In fact, does MyClass2 have to have an implementation of the doSomething(); method at all, as a doSomething(); method is inherited from MyClass1?
I've tried coding up little examples and things would appear to work as I expected.
In the 2nd piece of code, you don't have to implement a method signature mentioned in an interface, if the method has been implemented by the parent class.
Is that it? Or is there anything more to be aware of?
No, you've got it right. Of course, the point where you need to be careful is where there are two identical methods which are intended to have different meaning! At that point you need to change your design - though I don't think I've ever actually hit that problem in real code.