Question

I have some doubts while comparing C++ and Java multiple inheritance.

1. Even Java uses multiple, multi-level inheritance through interfaces – but why doesnt it use anything like a virtual base class as in C++ ? Is it because the members of a java interface are being ensured one copy in memory (they are public static final), and the methods are only declared and not defined ?

2. Apart from saving memory, is there any other use of virtual classes in C++ ? Are there any caveats if I forget to use this feature in my multiple inheritance programs ?

3. This one is a bit philosophical – but why didnt the C++ developers made it a default to make every base class, virtual ? What was the need of providing flexibility ?

Examples will be appreciated. Thanks !!

Answer 1

1) Java interfaces dont have attributes. One reason for virtual base classes in c++ is to prevent duplicate attributes and all the difficulties associated with that.

2) There is at least a slight performance penalty for using virtual base classes in c++. Also, the constructors become so complicated, that it is advised that virtual base classes only have no-argument constructors.

3) Exactly because of the c++ philosphy: One should not require a penalty for something which one may not need.