Theory of Programming Languages Chapter 12

What are the three defining characteristics of object-oriented programming?

Supports user-defined abstract data types, allows inheritance, and provides polymorphism based on dynamic method binding

What two concerns of procedure-oriented ADTs are addressed by inheritance?

Difficulty of reuse and lack of hierarchy

What is a class?

Object-oriented abstract data type

What is an object?

An instance of a class

What is a derived (child) class or subclass?

A class that inherits from another class

What is a parent (super) class?

The class that is inherited from

What is a method (member function)?

A subprogram that defines operations on objects

What is a message in OOP?

A call to a method

What is a message interface?

The collection of visible methods of an object

What is an API?

A collection of interfaces for multiple classes

What is method overriding?

A child class modifying an inherited method

What is a class variable?

One variable per class

What is an instance variable?

One variable per object

What is a class method?

A method that accepts messages sent to the class

What is an instance method?

A method that accepts messages sent to objects

What is single inheritance?

A class may inherit from only one superclass

What is multiple inheritance?

A class may inherit from more than one superclass

What are the two parts of a message?

Method name and destination object

What aspect of information hiding can complicate inheritance?

Access controls that hide entities from subclasses

What is a disadvantage of inheritance for software reuse?

Interdependence among classes that complicates maintenance

What is a polymorphic variable?

A variable that can refer to objects of its class or any of its subclasses

What distinguishes an abstract method from an ordinary method?

It has no body and is declared but not defined

What is an abstract class?

A class containing at least one abstract method

What is a concrete class?

A class containing only concrete methods

Why can an abstract class not be instantiated?

It provides only a partial implementation of a class

What is the primary disadvantage of Ruby being purely object-oriented?

Slow operations on simple objects

Which language has the more complete typing system, Java or C++?

C++

What does it mean for a subclass to be a subtype?

The subclass can be used wherever its parent type is expected

Where is a protected member visible?

Within the class, its subclasses, and related scopes depending on language

What are the access control levels in C++?

private, public, protected

What are the access control levels in Ruby?

public, protected, private

What are the access control levels in Java?

public, protected, package-private, private

Are subclasses always subtypes in C++?

Yes, with public derivation

Are subclasses always subtypes in Ruby?

No

Are subclasses always subtypes in Java?

Yes

Which provides broader access in Java: protected or package-private?

protected

What is the key difference between a public method in a package-private class and a package-private method in a public class?

Public methods in package-private classes can be accessed indirectly via public subclasses; package-private methods in public classes cannot be accessed outside the package

What is the primary advantage of multiple inheritance?

Writability

What is the primary disadvantage of multiple inheritance?

Cost

How does C++ support multiple inheritance?

Direct multiple inheritance

How does Ruby support multiple inheritance?

Mixins

How does Java support multiple inheritance?

Interfaces

What Ruby construct defines mixin methods?

module

How are Java interfaces treated similarly to Java classes?

Both can be used as variable types, parameter types, and generic type parameters

How are Java interfaces treated differently from Java classes?

A class may implement multiple interfaces but inherit from only one class

What is an advantage of supporting both static and dynamic method binding?

More efficient execution

Does C++ support static binding of method calls?

Yes

Does Ruby support static binding of method calls?

No

Does Java support static binding of method calls?

Yes

What is the default method binding in C++?

Static

What is the default method binding in Ruby?

Dynamic

What is the default method binding in Java?

Dynamic

What is a virtual function in C++?

A method that can be overridden to support polymorphism

What is a pure virtual function in C++?

A virtual function with no definition

What is an abstract class in C++?

A class containing at least one pure virtual function

What happens in Ruby if a method is not found in a class?

The method is searched for in the inheritance chain

Name one Java keyword that forces static binding.

final

Name another Java keyword that forces static binding.

static

Name a third Java keyword that forces static binding.

private

What is a nested class?

A class hidden from some other classes

In Java, where is a nested class visible?

In scopes determined by its access modifier

Does declaring a C++ variable of class type create an object?

Yes

Does declaring a C++ variable of pointer-to-class type create an object?

No

Does every class have a parent class in C++?

No

Does every class have a parent class in Ruby?

Yes

Does every class have a parent class in Java?

Yes

Can a default constructor be called implicitly in C++?

Yes

Can a default constructor be called implicitly in Ruby?

Yes

Can a default constructor be called implicitly in Java?

Yes

How is a parent constructor called explicitly in C++?

By adding the parent constructor call to the class declaration

How is a parent constructor called explicitly in Ruby?

By calling super

How is a parent constructor called explicitly in Java?

By calling super

What is the name of the constructor method in Ruby?

initialize

What two kinds of data are in a C++ Class Instance Record (CIR)?

Instance variables and a pointer to a vtable

What information does a C++ vtable contain?

Pointers to dynamically bound methods

What is the purpose of vtables?

Store method information once per class and share it among all objects

When might a CIR contain multiple vtable pointers?

When a class uses multiple inheritance

Are instance variables stored statically or dynamically in C++?

Dynamic

Are instance variables stored statically or dynamically in Ruby?

Dynamic

Are instance variables stored statically or dynamically in Java?

Static