1

Introduction to Classes and Objects

Chapter 3

Introduction to Classes and Objects

Chapter 3

2

Class vs Object

Blueprint House

Class Object

3

Class Definition/InterfaceGradeBook.h

Function prototypes

Forgetting ; is a syntax error

4

Class Implementation FileGradeBook.cpp

Define class member functions in separate

source-code file

Including the header file causes the class definitions

to be copied into the file

5

Constructor and Default Constructor

• C++ requires a constructor call for each object created– No return type, not even void– Compiler provides default constructor when a

constructor is not explicitly provided

• Default constructor– Constructor with no parameters– Two ways to provide default constructor

• The compiler implicitly creates a default constructor in a class without a constructor (may contain garbage value for its data members)

• The programmer explicitly defines a constructor that takes no arguments

6

Data Member and Member Function

• Data members– Variables declared inside a class definition but outside the

class’s member function body– Represents the attributes of the class– Each object has its own copy of data members

• Member functions– Get functions (accessors) to access private data members– Set functions (mutators) to change the values of private data

members– All objects of the same class share one copy of each member

function

7

Scope Resolution Operator

• Scope resolution operator (::) is used to define the member functions outside the class

• A token to allow access to static members of a class

• Scope resolution operator is preceded by a class name

Example: void GradeBook::setCourseName(string name) {…}string GradeBook:getCourseName() {…}

8

Dot Member Selection Operator

• Dot operator (.) is used to access a member of an object

• Preceded by an object name

• ExamplegradeBook1.setCourseName(“COMP1520: C++”);

gradeBook1.displayMessage();

9

Main Program (Client Code)Testing Class GradeBook

10

Class Diagram for GradeBook Class

Minus indicates a private member

Plus indicates public members

Name of the class in boldface

Class attributes

Class operations

11

Separating Interface from Implementation

• Interfaces– Define and standardize the ways in which things interact with each other– Describes what services class’s client can use and how to request those services– Not how the class carries out the services– Consists only a class’s public members

• Why separate interface from the implementation– Ensures programmers do not write client code that depends on the class’s

implementation details– Client codes are less likely to break if the implementation changes– The class is reusable– The clients of the class know what member functions the class provides, how to

call them and what return types to expect– The clients do not know how the class's member functions are implemented

• How– Defining a class’s interface with function prototypes

• Function prototypes describes the class's public interface without revealing the class's member function implementations

– Defining member functions in a separate source-code file

12

How Header Files Are Located

• When the preprocessor encounters a header file name in quotes (e.g., "GradeBook.h"), the preprocessor

– Attempts to locate the header file in the same directory as the file in which the #include directive appears.

– If failed, searches for it in the same location(s) as the C++ Standard Library header files.

• When the preprocessor encounters a header file name in angle brackets (e.g., <iostream>), it

– assumes that the header is part of the C++ Standard Library

13

The Compilation and Linking Process

14

Unified Modeling Language (UML)

• General-purpose modeling language

• Create abstract model of a system using graphical notation

• Used to specify, visualize, construct, and document software-intensive systems

• Allow software developers to concentrate more on design and architecture

15

UML Diagrams

16

Software Engineering Case Study: ATM Class Diagram

• Determine the classes used in the system– ATM– Screen– Keypad– Cash dispenser– Deposit slot– Account– Bank database– Balance inquiry– Withdrawal– Deposit

17

Representing a class in the UML using a class diagram

Name of the class

Class’s attributes

Class’s operations

Compartments can be suppressed to create more readable diagrams.

18

Association between Classes

Solid line represents association between classes

Multiplicity value

One object of class ATM executes zero or one objects of class Withdrawal.

19

Multiplicity Types

Symbol Meaning

0 None

1 One

m An integer value

0..1 Zero or one

m, n m or n

m..n At least m, but not more than n

* Any nonnegative integer (zero or more)

0..* Zero or more (identical to *)

1..* One or more

20

Composition Relationship

Composition relationship or “has-a”

relationship

1. The diamond can be placed on only one end of the association line.2. The whole is responsible for creating and destructing its parts.3. A part may belong to only one whole at a time.

An ATM has a screen, a keypad, a cash dispenser and a deposit slot.

21

Class Diagram for the ATM System Model

22

Class Diagram Showing Composition Relationship of a Class Car