Ch 7-1. Object-Oriented Programming and Classes

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Ch 7-1. Object-Oriented

Programming and Classes

2014-1 Programming Language

May 10, 2014

Prof. Young-Tak Kim

Advanced Networking Technology Lab. (YU-ANTL) Dept. of Information & Comm. Eng, Graduate School,

Yeungnam University, KOREA

(Tel : +82-53-810-2497; Fax : +82-53-810-4742

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Outline

Classes

z Object-Oriented Programming Concept

z Defining, member functions

z Public and private members

z Accessor and mutator functions

z Structures vs. classes

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Advanced Networking Tech. Lab.

Yeungnam University (YU-ANTL) ch 7-1 - 3 Programming LanguageProf. Young-Tak Kim

Major Considerations in

Large-scale Software System Developments

Procedure of Design, Development and Maintenance

of Large-Scale Software

z Requirements analysis

z Software design

z Unit testing

z Component testing

z System testing

z Maintenance

Major Considerations

z Clear unit/component/sub-system interface

z Stability of unit/component/sub-system

z Easy modification/update of unit/component/sub-system without

great impact on other parts

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Object-Oriented Programming (OOP)

Object-Oriented Programming Object-oriented

programming (

OOP

) (

객체 지향형 프로그래밍

)

z an approach to designing

modular

,

reusable

software systems

z a

programming paradigm

that represents the concept of "

objects

"

that have

data fields

(attributes that describe the object) and

associated procedures known as

methods

z Objects, which are usually

instances

of

classes

, are used to interact

with one another to design applications and computer programs

Goals of object-oriented programming :

z

Increased understanding: rather than talking about database

tables and programming subroutines, the developer talks about

things the user is familiar with: objects from their application domain

z

Ease of maintenance

and

adoption of new technologies by

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Classes

Similar to structures

z Not only, just member data

z But also, adds member functions

Integral to object-oriented programming

z Focus on objects

Object: Contains data and operations

Class: mold (주형 형틀, 거푸집) to instantiate an object

In C++,

variables

of

class type

are

objects

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Class Definitions

Defined similar to structures

Example:

class DayOfYear

// name of new class type

{

public:

// access specifier

void output();

// member function

int month;

// data member

int day;

// data member

};

Notice only member function’s prototype

z Function’s implementation is elsewhere

(7)

Declaring Objects

Declared same as all variables

z Predefined types, structure types

Example:

DayOfYear today, birthday

;

Declares two objects of class type DayOfYear

Objects include:

z Data (attribute)

Members: month, day

z Operations (member functions)

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Class Member Access

Members accessed same as structures

Example:

today.month

today.day

z And to access member function:

(9)

Class Member Functions

Must define or "implement" class member

functions

Like other function definitions

z Can be after main() definition

z Must specify class:

void DayOfYear::output()

{

…

}

::

is

scope resolution operator

Instructs compiler "what class" member is from

Item before :: called type qualifier

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Class Member Functions Definition

Notice output() member function’s

definition (in next example)

Refers to member data of class

z No qualifiers

Function used for all objects of the class

z Will refer to "that object’s" data when invoked

z Example:

today.output();

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Complete Class Example:

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Display 6.3 Class With a Member Function (3 of 4)

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Dot

(.) operator and

Scope Resolution (::)

Operator

Used to specify "of what thing" they are

members

Dot operator (.) :

z Specifies member of particular object

Scope resolution operator (::)

z Specifies what class the function definition comes from

class DayOfYear {

public: // access specifier

void output(); // member function

int month; // data member

int day; // data member

}; DayOfYear::output() { } DayOfYear today; today.year = 2014; today.month = 5;

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A Class’s Place

Class is full-fledged type!

z Just like data types int, double, etc.

Can have variables of a class type

z We simply call them "objects"

Can have parameters of a class type

z Pass-by-value

z Pass-by-reference

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Encapsulation

Any data type includes

z Data (range of data)

z Operations (that can be performed on data)

Example:

int

data type has:

Data: +-32,767

Operations: +,-,*,/,%, logical, etc.

Same with classes

z But WE specify data, and the operations to

be allowed on our data!

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Abstract Data Type (ADT)

"Abstract"

z Programmers don’t know details

Abbreviated "ADT"

z Collection of data values together with set

of basic operations defined for the values

ADT’s often "language-independent"

z We implement ADT’s in C++ with classes

C++ class "defines" the ADT

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More on Encapsulation

Encapsulation

z Means "bringing together as one"

Declare a class Æ get an object

Object is "encapsulation" of

z Data values (attributes)

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Principles of OOP

Encapsulation

z Bring together data and operations,

but keep "details" hidden

Information Hiding

z Details of its implementations and its operations work

not known to "user" of class

Data Abstraction

z Details of how data is manipulated within

ADT/class not known to user

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Encapsulation in Object

Encapsulation and protection of private data

Object

PrivateData Members Private Member Functions - house keeping

Public Member Functions

- get() // read with validity check - set() // write with validity check Friend Functions

- cin >> // standard input - cout << // standard output

interface to outside

outside

program

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Public and Private Members

Data in class almost always designated

private in definition!

z Upholds principles of OOP

z Hide data from user

z Allow manipulation only via operations

Which are member functions

Public items (usually member functions)

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Public and Private Example

Modify previous example:

class DayOfYear

{

public:

void input();

void output();

private:

int month;

int day;

};

Data now private

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Public and Private Example 2

Given previous example

Declare object:

DayOfYear today;

Object

today

can ONLY access

public members

z cin >> today.month;

// NOT ALLOWED!

z cout << today.day;

// NOT ALLOWED!

z Must instead call public operations:

today.input();

today.output();

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Public and Private Style

Typically place public first

z Allows easy viewing of portions that can be

USED by programmers using the class

z Private data is "hidden", so irrelevant to users

Can mix and match public and private

Outside of class definition,

cannot change (or even access) private

data

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Accessor and Mutator Functions

Object needs to "do something" with its

data

Accessor

member functions

z Allow object to read data

z Also called "get member functions"

z Simple retrieval of member data

Mutator

member functions

z Allow object to change data

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// Display 6.4 Class with Private Members

#include <iostream> #include <cstdlib> using namespace std; class DayOfYear { public: void input( ); void output( );

void set(int newMonth, int newDay);

//Precondition: newMonth and newDay form a possible date. void set(int newMonth);

//Precondition: 1 <= newMonth <= 12

//Postcondition: The date is set to the first day of the given month. int getMonthNumber( ); //Returns 1 for January, 2 for February, etc. int getDay( );

private:

int month; int day;

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int main( )

{

DayOfYear today, bachBirthday; cout << "Enter today's date:₩n"; today.input( );

cout << "Today's date is "; today.output( );

cout << endl;

bachBirthday.set(3, 21);

cout << "J. S. Bach's birthday is "; bachBirthday.output( );

cout << endl;

if ( today.getMonthNumber( ) == bachBirthday.getMonthNumber( ) && today.getDay( ) == bachBirthday.getDay( ) )

cout << "Happy Birthday Johann Sebastian!₩n"; else

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Yeungnam University (YU-ANTL) ch 7-1 - 29 Programming LanguageProf. Young-Tak Kim //Uses iostream and cstdlib:

void DayOfYear::set(int newMonth, int newDay)

{

if ((newMonth >= 1) && (newMonth <= 12)) month = newMonth;

else {

cout << "Illegal month value! Program aborted.₩n"; exit(1);

}

if ((newDay >= 1) && (newDay <= 31)) day = newDay;

else {

cout << "Illegal day value! Program aborted.₩n"; exit(1);

} }

//Uses iostream and cstdlib:

void DayOfYear::set(int newMonth)

{

if ((newMonth >= 1) && (newMonth <= 12)) month = newMonth;

else {

cout << "Illegal month value! Program aborted.₩n"; exit(1);

}

day = 1; }

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int DayOfYear::getMonthNumber( ) { return month; } int DayOfYear::getDay( ) { return day; }

//Uses iostream and cstdlib: void DayOfYear::input( ) {

cout << "Enter the month as a number: "; cin >> month;

cout << "Enter the day of the month: "; cin >> day;

if ((month < 1) || (month > 12) || (day < 1) || (day > 31)) {

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void DayOfYear::output( )

{

switch (month) {

case 1: cout << "January "; break; case 2: cout << "February "; break; case 3: cout << "March "; break; case 4: cout << "April "; break; case 5: cout << "May "; break; case 6: cout << "June "; break; case 7: cout << "July "; break; case 8: cout << "August "; break; case 9: cout << "September "; break; case 10: cout << "October "; break; case 11: cout << "November "; break; case 12: cout << "December "; break; default:

cout << "Error in DayOfYear::output. Contact software vendor."; } // end switch

cout << day; }

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Separation of

Interface

and

Implementation

User of class need not see details of how

class is implemented

z Principle of OOP Æ encapsulation

User only needs "rules"

z Called "

interface

" for the class

In C++ Æ public member functions and

associated comments

Implementation

of class is

hidden

z Member function definitions elsewhere

z User need not see them

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Structures vs. Classes

Structures

z Typically all members public

z No member functions

Classes

z Typically all data members private

z Interface member functions public

Technically, same

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Thinking Objects

Focus for programming changes

z Before Æ algorithms center stage

z Object-Oriented Programming (OOP) Æ data is focus

Algorithms still exist

z They simply focus on their data

z Are "made" to "fit" the data

Designing software solution

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Summary 7-1-1

Structure

is collection of different types

Class

used to combine data and functions

into single unit ->

object

Member variables and member functions

z Can be public Æ accessed outside class

z Can be private Æ accessed only in a member

function’s definition

Class and structure types can be formal

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Summary 7-1-2

C++ class definition

z Should separate two key parts

Interface: what user needs

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Homework 7-1

7-1.1 Structure of planets in the solar system.

Each planet has following information:

Name : a character string of less than 10 characters

Relative-Mass : double type value of mass relative to Earth

Distance from sun : double type value of mean distance from sun in [10

6

Km]

1) Design a structure for a planet with the information of planets.

struct Planet

{

char name[10];

double relativeMass;

double distance;

};

(38)

2) Using the structure designed above, make an array Planet

solar_planet[9], and initialize the array from an input file

“solar_planet.dat” which contains following data :

Name of Planet Relative Mass Distance from Sun

Mercury 0.0558 57.9 Venus 0.815 108 Earth 1.0 150 Mars 0.107 228 Jupiter 318 778 Saturn 95.1 1430 Uranus 14.5 2870 Neptune 17.2 4500 Pluto 0.11 5900

3) Using the solar_planet[ ] array, make a sorted list of solar planets in

non-decreasing order of relative mass. Output the result to

“sortedSolarPlanet.dat” in the same format of input file.

4) Using the solar_planet[ ] array, make a sorted list of solar planets in

non-decreasing order of distance from Sun. Output the result to

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7-1.2 Write a header file “

Class_Planet.h

” with a “

class Planet

” with

following members:

(1) Private Data members:

. name: a character string of less than 10 characters

. relativeMass: double type value of mass relative to Earth

. distance: double type value of mean distance from sun in [106 _Km]

(2) Public methods:

. constructor: constructs the object instance of Planet with given arguments . destructor: destructs the object instance of Planet

. print(): printout the name, relative mass and distance of the planet object . setName(): set name that truncate the name if the length is longer than 10

characters

. setRelMass(): set relative mass when the passed value is greater than 0 and less than 100; otherwise the value is set to 0

. setDist(): set distance when the passed value is greater than 0 and less than 10,000.

. getName(): returns the name of the planet . getRelMass(): returns the relative distance . getDistance(): returns the distance

(40)

7-1.3 Write a header file “

SolarSystem

.h” that includes

“

Class_Planet

.h” and contains a “

class SolarSystem

” with

following members:

(1) Private Data members:

. planets: array of planet object instances

(2) Public methods:

. constructor: constructs the object instance of SolarSystem

. destructor: destructs the object instance of SolarSystem

. addPlanet: create a new planet with given parameters for the planet

. deletePlanet: delete a planet with the given planet name

. sortPlanetsByName(): sort the planets in the solar system in the

non-decreasing order of name

. sortByRelMass(): sort the planets in the solar system in the

non-decreasing order of relative mass

. sortByDistance():sort the planets in the solar system in the

non-decreasing order of distance

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7-1.4 Write a “

solarSystem.cpp

” that includes the header file

“

Class_Planet.h

” and “

solarSystem.h

”.

(1) This program reads in “solarSystem.dat” file to create & initialize the

solar system.

(2) It prints out the sorted list of planets in the solar system:

i) in non-decreasing order of name,

ii) in non-decreasing order of relative mass,

iii) in non-decreasing order of distance.

(3) Contents of “solarSystem.dat” file

Name of Planet Relative Mass

Distance from Sun

Mercury

0.0558

57.9

Venus

0.815

108

Earth

1.0

150

Mars

0.107

228

Jupiter

318

778

Saturn

95.1

1430

Uranus

14.5

2870

Neptune

17.2

4500

Pluto

0.11

5900

Ch 7-1. Object-Oriented Programming and Classes