Database Abstraction and OOP

Question 1

What are some benefits of abstractions?

Answer 1

• Easier to think about
• Prevent access to things you shouldn’t see
• plug compatibility (replacement of pieces often without recompilation)
• Division of laber in software projects

Question 2

What are the three key factors in OOP?

Answer 2

• Encapsulation (data hiding)
• Inheritance
• Dynamic method binding

Question 3

Can you tell at compilation time what will be printed on the last line of the code below?

Answer 3

No. It depends if runtime uses static or dynamic binding.

Question 4

Can x access field b?

x.b

Answer 4

No. Only the child (subclass) knows that the record goes farther the parent does.

Question 5

What are dynamically bound methods called in C++?

Answer 5

Virtual

Question 6

In C++, how are default methods bounded?

Answer 6

Statically

Question 7

In Java, how are default methods bounded?

Answer 7

Dynamically (virtual)

Question 8

(T/F) Non-virtual functions (static) require no space at run time. Explain.

Answer 8

True

The compiler just calls the appropriate version, based on the static type of the variable.

Question 9

(T/F) Virtual functions are passed an extra, hidden, paramter.

Answer 9

True

Question 10

Virtual functions in C++ have a dispatch table (vtable) for the class.

(T/F) Subclasses create their own vtables.

Answer 10

True

Question 11

What happens if the order of the vtable methods get reordered?

Answer 11

All clients will have to recompile.

Question 12

In Java, reordering the vtable and loosing linkage is resolved how?

Answer 12

Java uses symbolic links which are resolved after compile time to find the offset into the method table.

Question 13

Give an example of repeated inheritance.

Answer 13

• Shared inheritance
• Replicated inheritance

Question 14

What is a mix-in inheritance?

Answer 14

Single inheritance from on “real” base class, plus multiple inheritance from abstract classes (interfaces in Java).

Question 15

Does a constructor allocate space?

Answer 15

No. It initializes the object.

Question 16

(T/F) In C++, when an object of a derived class is created, the constructors for any base class will be executed before the constructor for the derived class.

Answer 16

True

Question 17

(T/F) In C++ finalization, destructors for superclasses are called first followed by the destructor for the subclass.

Answer 17

False

Question 18

Genericity VS Inheritance

Describe Genericity.

Answer 18

Parametric polymorphism:

• Type is explicitly parameterized
• Single copy of source code allows generation of versions that allow multiple types

Think of lists. (See horizontal relationship)

Question 19

Genericity VS Inheritance

Describe Inheritance.

Answer 19

Subtype polymorphism:

• Can use an instance of a subclass wherever a class is expected.

See vertical relationship.