Classes and Abstraction in Object-Oriented Design

Object Oriented Design (OOD)

A problem solving methodology

Objects

Components of a solution

Class

A collection of a fixed number of components

Member

Component of a class

Class Definition

Defines a data type; no memory is allocated

Class member

Can be a variable or a function

Variable member of a class

It's declared like any variable; you cannot initialize a variable when you declare it

Function member of a class

Function prototype is listed; function members can (directly) access any member of the class

Private member

Member cannot be accessed outside of class

Public member

Member that can be accessed outside of class

Protected member

Member that can be accessed by derived classes

Unified Modeling Language

Used to graphically describe a class and its members

Class variable

Called a class object or class instance

Member access operator

The dot (.) is used to access class members

Automatic object

Created when the declaration is reached and destroyed when the surrounding block is exited

Static object

Created when the declaration is reached and destroyed when the program terminates

Passing by value

Contents of data members of the actual parameter are copied into the corresponding data members of the formal parameter

Passing by reference

The formal parameter receives only the address of the actual parameter

Const in formal parameter

Used to prevent changes to the actual parameter when passing by reference

Accessor Function

Member Function that only accesses the value(s) of member variable(s)

Mutator Function

Member Function that modifies the value(s) of member variable(s)

Constant Function

Member Function that cannot modify member variables

Instance Variables

Each object has its own copy of the member variables (hr, min, sec)

Scope resolution operator

Used to access identifiers local to the class

Client of a class

A program that uses/manipulates objects of a class

Public member

Member can be accessed outside of class

Protected member

Member can be accessed by derived classes

Member access operator

The dot (.) is used to access members of a class

Constant Function

Member Function that cannot modify member variables; use const in function heading

Order of Members

C++ has no fixed order in which to declare private and public functions.

Default Member Access

By default, all members of a class are private.

Public Member Access

Use the member access specifier public to make a member available for public access.

Constructors

Use constructors to guarantee that member variables of a class are initialized.

Types of Constructors

Two Types of Constructors: a) Default Constructor (no parameters), b) Parameterized Constructor (with parameters).

Constructor Naming

Name of Constructor = Name of the Class.

Constructor Type

A constructor has no type.

Multiple Constructors

A class can have more than one constructor; each must have a different formal parameter list.

Constructor Execution

Constructors execute automatically when a class object enters its scope.

Constructor Invocation

A constructor is automatically executed when a class variable is declared.

Specific Constructor Invocation

Because a class may have more than one constructor, you can invoke a specific constructor.

Default Constructor Invocation Syntax

To invoke the default constructor: className classObjectName.

Parameterized Constructor Invocation Syntax

Syntax: className classObjectName (argument1, argument2, ...).

Argument Matching

Number and type of arguments should match the formal parameters of one of the constructors.

Type Conversion

Otherwise, C++ uses type conversion and looks for the best match; any ambiguity causes a compile-time error.

Default Parameters in Constructors

Constructor can have default parameters; rules for declaring formal parameters are the same as for declaring default parameters in a function.

Default Constructor Definition

A constructor with no parameters or with all default parameters.

Default Constructor Provision

If a class has no constructor(s), C++ provides the default constructor; however, the object declared is still uninitialized.

Absence of Default Constructor

If a class includes constructors(s) with parameter(s), but not the default constructor, C++ does not provide the default constructor.

Array of Class Objects

If you declare an array of class objects, the class should have the default constructor.

Destructor

Functions without any type.

Destructor Naming

Name of a destructor is the character "~" followed by the class name (ex: ~clockType).

Single Destructor

A class can only have one destructor; the destructor has no parameters.

Destructor Execution

Destructor automatically executes when class object goes out of scope.

Abstraction

Separating design details from usage; separating the logical properties from the implementation details.

Abstract Data Type (ADT)

Data type that separates the logical properties from the implementation details.

Struct vs Class

By default, members of a struct are public; private specifier can be used in a struct to make a member private.

Members of Class

By default, members of a class are private.

Capabilities of Classes and Structs

Classes and structs have the same capabilities.

Expanded Struct Definition

In C++, the definition of a struct was expanded to include member functions, constructors, and destructors.

Using Struct

If all member variables of a class are public and there are no member functions, use a struct.

Information Hiding

Hiding the details of the operations on the data.

Interface

Contains the specification details.

Implementation File

Contains the implementation details (file extension is .cpp).

Function Prototypes in Header

In header file, include function prototypes and comments that briefly describe the functions.

Precondition

A statement specifying the condition(s) that must be true before the function is called.

Postcondition

A statement specifying what is true after the function call is completed.

Static Members

Use the keyword static to declare a function or variable of a class static.

Accessing Static Members

A public static function or member of a class can be accessed using the class name and the scope resolution operator.

Static Member Variables

Static member variables of a class exist even if no object of that class type exists.

Non-static Member Variables

Multiple objects of a class each have their own copy of non-static member variables.

Shared Static Members

All objects of a class share any static member of the class.

Class Summary

Class: collection of a fixed number of components.

Class Members

Members: components of a class; accessed by name; 3 Categories: public, private, protected.

Class Variables

Class variables are called class objects or simply objects.

Built-in Operations on Classes

The only built-in operations on classes are assignment and member selection.

Instance Variables

Instance variables: non-static data members.