Object Oriented skills

The object oriented paradigm is now present in almost every programming language. With bad or good support, most of them cover at least the basic principles. It is true that knowing a few programming skills can help you program in any language but the flavours of OO can be quite different from language to language and a programmer needs to understand at least the basic concepts of each to write decent code.

1. The object A must read a value in object B but that value is protected, what would you do?
2. On a generic algorithm, I need to define series of prerequisites to be followed for any class that might be used by it, what would you do?
3. Tell me the differences between classes and structures.
4. In the first question, suppose the object A belongs to the only class that should actually read that value, what would you do in that case?

1. In C++ you can have multiple inheritance but in Java 1.4 you can't. What would you use to mimic this behaviour? What are the pro and cons?
2. In Perl, object orienting is mimicked by using native hashes as attributes and function pointers, what's the problem with this?