Chapter 12

Question 1

Which languages are considered pure OOP languages?

Answer 1

Smalltalk + Ruby

Question 2

What must any OOP language support?

Answer 2

ADTs
Inheritance
Polymorphism

Question 3

What is good about inheritance?

Answer 3

Increases productivity from reuse

Question 4

Problem with basic ADTs?

Answer 4

Difficult to reuse without some changes

Question 5

What are some OO concepts?

Answer 5

ADTs aka classes
Class instances aka objects
Class inheritance aka subclass/ derived class + superclass . parent class
Subprograms defining operations on objects aka methods aka member functions

Call to methods aka messages
Collection of object methods aka message interface
2 part messages aka method name + destination object (myObject.print(12))
Access control in inheritance
Overriding methods

Question 6

What are the 2 kinds of variables in a class?

Answer 6

Class variable ( one per class )
Instance variables ( one per object )
Same with methods

Question 7

Disadvantage of inheritance?

Answer 7

Complicate maintenance, interdependencies among classes

Question 8

What type of binding is a polymorphic reference?

Answer 8

Dynamic Binding

Question 9

What is a abstract method?

Answer 9

Only define protocol, no definition

Question 10

What is a abstract class?

Answer 10

Include at least one abstract method
Cannot be instantiated

Question 11

What are some design issues for OOP languages?

Answer 11

Single vs multiple inheritance
Dynamic vs static binding
Nested classes
Are subclasses subtypes?

Question 12

What is good and bad when everything is an object?

Answer 12

Good: Elegance + pure uniformity
bad: simple operations are slow

Question 13

What is good and bad about adding objects to a complete typing system?

Answer 13

Good: simple operations are fast
Bad: Results in confusing type system

Question 14

Good and Bad about using imperative typing system for primitives and making everything else objects? (Java)

Answer 14

Good: Simple operations are fast, but typing system remains relatively small
Bad: 2 type systems have to mix

Question 15

When is a derived class a subtype?

Answer 15

If is has a “is-a” relationship with the parent class

Question 16

Good and Bad of Multiple inheritance?

Answer 16

Good: convenient + valuable
Bad: Complexity, name collisions. potential inefficiency

Question 17

What is the problem with diamond inheritance?

Answer 17

It always produces a type problem

Question 18

Should every binding of a message to a method be dynamic?

Answer 18

Only dynamic binding is inefficient
No dynamic binding = no advantages

Question 19

What is a problem with nested classes?

Answer 19

Deciding visibility of members

Question 20

When do you use nested classes?

Answer 20

When a new class is only needed by one class

Question 21

What are the 2 object initialization types?

Answer 21

Explicit and implicit( only if there exists a default constructor in the language )

This can also lead to explicit + implicit initialization of subclass objects

Question 22

Does Smalltalk have any characteristics of imperative languages?

Answer 22

No. Its a pure OOP language

Question 23

How are objects accessed in Smalltalk?

Answer 23

Typeless reference variables

Question 24

Is Smalltalk deallocation implicit or explicit?

Answer 24

implicit
Uses a garbage collector which can be slow

Question 25

Do Smalltalk bind messages to methods statically or dynamically?

Answer 25

Dynamically

Question 26

How does dynamic message binding impact Smalltalk language evaluation?

Answer 26

Decreases readability but increases writability and reliability

Question 27

How does the lack of multiple inheritance affect the language evaluation criteria?

Answer 27

Decreased writability and readability, increases reliability (no diamond problem)

Question 28

What is one of the most widely used OOP languages?

Answer 28

C++

Question 29

How is C++ better than Smalltalk?

Answer 29

Faster execution

Question 30

2 types of inheritance access controls in C++?

Answer 30

Public derivation Private derivation

Question 31

When does a designer decide what type of message binding he will use?

Answer 31

At class design time

Question 32

Which is faster? Dynamic message binding or static message binding?

Answer 32

Static

Question 33

How do you "signal" dynamic binding in C++?

Answer 33

virtual

Question 34

Which draw will be called if objects are allocated from the stack? (static) Circle circ; // Allocates a Circle object from the stack Rectangle rect; // Allocates a Rectangle object from the stack rect = circ; // Copies data member values from circ object rect.draw();

Answer 34

The draw from rectangle

Question 35

Does Java support single or multiple inheritance?

Answer 35

Only single

Question 36

Does Java use dynamic or static message binding?

Answer 36

Only dynamic

Question 37

What is the advantage of using "new" when overriding a methods definition in C#?

Answer 37

No accidental method hiding

Question 38

What does "override" keyword do to readability writability and reliability?

Answer 38

Reliability + Readability = increased Writability = no significant impact

Question 39

What are the implications of all data being private in Ruby classes, in terms of the language evaluation criteria?

Answer 39

Decreased writability, increased reliability