41173772 Object Oriented Programming With C

Chapter 4

Object Oriented Programming with C#

• A Class is a customer user-defined type that is composed of data and functions that act on this data.

Employee

attributes:

string fullName

int empID

float currPay

Methods

Employee()

Employee(string fullName, int empID, float currPay)

void GiveBonus(float amout)

Void DisplayStats();

Method Overloading• When a class has a set of identically named members that differ by the

number or type of parameters, the member in question is said to be overloaded.Eg:

class Triangle{

public void Draw( int x, int y, int height, int width);public void Draw( float x, float y, float height, float

width);public void Draw(Point upperLeft, Point bottomRight);public Draw (Rect r);

}• When a class member is overloaded, the return type alone is not unique

enough.public float GetX();public int GetX();

Self Reference

• “this” keyword• This keyword is used whenever the reference is to be made to the

current object.• Static member functions of a type cannot use “this” keyword.

public Employee(string FullName, int empID, float currPay){

this.fullName = FullName;this.empID = empID;this.currPay = currPay;this.empSSN = ssn;

}

public Employee(string fullName) : this(fullName, 3333, 0.0F) { }

Default public Interface

• Set of public members that are directly accessible from an object variable. – Method visibility – units that model the behavior of the

class.– Properties visibility – Accessor and mutator functions– Field Data visibility - Data

– Type visibility – which parts of the system can create type themselves. If not specified, it is assumed to be internal.

public class HelloClass

{…

}– This would mean that all .Net assemblies can use this

class.– Any .NET type can be defined to have public or

internal visibility.

using System;namespace Hellotypes{

internal struct x{

private int myX;public int GetMyX() { return myX;}public x(int x) {myX = x;}

}internal enum Letters{a=0, b=1, c=2}

public class HelloClass{

public static int Main(string[] args){

X theX = new X(26);Console.WriteLine(“{0}\n{1}”, theX.GetMyX(), Letters.b.toString());return 0;

}}

Pillars of OOP

• Encapsulation: how well does this language hide the object’s internal implementation?

• Inheritance: How does the language promote code reuse?– (Classical) Is-a – Eg: Hexagon-shape-object

– has-a relationship –Eg: car-radio

• Polymorphism: How does this language let you treat related objects in a similar way?– Classical – Base class defines a set of members that can be overridden

by subclass. Eg; Draw

– Ad-hoc – Late binding

Encapsulation

• Black box programming• An object’s internal data should not be directly

accessible from an object instance.– public– private– protected– protected internal

• Define the data fields as private– Define a pair of accessor and mutator methods– Define a named property

using system;public class Department{

private string departname;// Accessor.public string GetDepartname(){

return departname;}// Mutator.public void SetDepartname( string a){

departname=a;}public static int Main(string[] args){

Department d = new Department(); d.SetDepartname("ELECTRONICS"); Console.WriteLine("The Department is :"+d.GetDepartname()); return 0;

}}

public string Name

{

get { return fullName; }

set { fullName = value;}

}

// Property for the empID.

public int EmpID

{

get {return empID;}

set

{

empID = value;

}

}

// Property for the currPay.

public float Pay

{

get {return currPay;}

set {currPay = value;}

}

class TimePeriod{ private double seconds;

public double Hours { get { return seconds / 3600; } set { seconds = value * 3600; } }}class Program{ static void Main() { TimePeriod t = new TimePeriod();

// Assigning the Hours property causes the 'set' accessor to be called. t.Hours = 24;

// Evaluating the Hours property causes the 'get' accessor to be called. System.Console.WriteLine("Time in hours: " + t.Hours); }}

• Write a C# class Student with the following attributes– usn (string)– attendance (int)– internalMarks (float)

• Create mutators and accessors to access usn and attendance.

• Create a property to access internalMarks. • The attendance and internalMarks returned should be in

percentage. (assume total no of classes = 60 and Max internal = 25)

• Write a main function that to demonstrate the usage.

C# Inheritance Support

using System;

public class Employee

{

// protected data for kids.

protected string fullName;

protected int empID;

private float currPay;

}

namespace Employees{

public class Manager : Employee{

private ulong numberOfOptions;public ulong NumbOpts {

get {return numberOfOptions;}set { numberOfOptions = value;}

}}public class SalesPerson : Employee{

protected int numberOfSales;public int NumbSales {

get {return numberOfSales;}set { numberOfSales = value;}

}}

}

public static int Main(string[] args)

{

SalesPerson stan = new SalesPerson();

stan.EmpID = 100;

stan.setFullName("Stan the Man");

stan.NumbSales = 42;

stan.currPay; //Error

return 0;

}

public class Radio

{

public void TurnOn(bool on)

{

if(on)

Console.WriteLine("Jamming...");

else

Console.WriteLine("Quiet time...");

}

}

public class Car {

private int currSpeed;private int maxSpeed;private string petName;bool carIsDead;public Car() {

maxSpeed = 100;carIsDead = false;

}public Car(string name, int max, int curr) {

currSpeed = curr;maxSpeed = max;petName = name;carIsDead = false;

}// A car has-a radio.private Radio theMusicBox = new Radio();

public void CrankTunes(bool state){

// Tell the radio play (or not).// Delegate request to inner object.theMusicBox.TurnOn(state);

}public void SpeedUp(int delta){

// If the car is dead, just say so...if(carIsDead){

Console.WriteLine("{0} is out of order....", petName );}else // Not dead, speed up. {

currSpeed += delta;if(currSpeed >= maxSpeed) {

Console.WriteLine("Sorry, {0} has overheated...", petName );carIsDead = true;

}else

Console.WriteLine("=> CurrSpeed = {0}", currSpeed); } }

public class CarApp{

public static int Main(string[] args){

// Make a car.Car c1;c1 = new Car("SlugBug", 100, 10);

// Jam some tunes.Console.WriteLine("***** Turing on radio for SlugBug *****");c1.CrankTunes(true);

// Speed up.Console.WriteLine("\n***** Speeding up *****");for(int i = 0; i < 10; i++)

c1.SpeedUp(20);

// Shut down.Console.WriteLine("\n***** Turing off radio for SlugBug *****");c1.CrankTunes(false);return 0;

} }

• Create a namespace college

• Base class: Person – Attributes: name, address, Phone

• Derived class: Student– Attributes: usn, branch, subjectsTaken

• Derived class: Teacher– Attributes: subjectTaught,

• Helper class: Subject– Attributes: SubjectName, MaxAtt, MaxIM

• Create a Main function to – create an instance of a student, initialize it to your details. – create an instance of a teacher, initialize it to a teacher’s details.– Display all the details.

using System;namespace College{ public class Person { protected string name; protected string address; protected string phone; public Person(string newName, string newAddress, string newPhone) { this.name = newName; this.address = newAddress; this.phone = newPhone; } public string getName() { return name; } public string getAddress() { return address; } public string getPhone() { return phone; } }

class Subject { private string subjectName; private int MaxAtt; private int MaxIM; public Subject(string newSubjectName, int newMaxAtt, int newMaxIM) { this.subjectName = newSubjectName; this.MaxAtt = newMaxAtt; this.MaxIM = newMaxIM; } public string getsubjectName() { return subjectName; } public int getMaxAtt() { return MaxAtt; } public int getMaxIM() { return MaxIM; } }

class Student : Person { private string usn; private string branch; private Subject subjectsTaken;

public Student(string newName, string newAddress, string newPhone, string newUsn, string newBranch, Subject mySubject): base(newName, newAddress, newPhone)

{ this.usn = newUsn; this.branch = newBranch; this.subjectsTaken = mySubject;

}

public string getUsn() { return usn; } public string getBranch() { return branch; } public Subject getSubjectTaken() { return subjectsTaken; } }

class Teacher : Person { private Subject SubjectTaught; public Teacher(string newName, string newAddress, string newPhone, Subject

mySubject) : base(newName, newAddress, newPhone) { this.SubjectTaught = mySubject; } public Subject getSubjectTaught() { return SubjectTaught; } }

class StudentApp { public static void Main() { Subject cSharp = new Subject("C#", 64, 25); Student stud1 = new Student("Sujatha", "Anandnagar", "9885655627", "1AT02CS007", "CSE",

cSharp); Teacher t1 = new Teacher("Seema", "Hebbal", "080-765676", cSharp);

Console.WriteLine("Student Name:" + stud1.getName()); Console.WriteLine("Student Address:"+stud1.getAddress()); Console.WriteLine("Student Phone:" + stud1.getPhone()); Console.WriteLine("Student USN:" + stud1.getUsn()); Console.WriteLine("Student branch:" + stud1.getBranch()); Console.WriteLine("Student Subject Taken:" + stud1.getSubjectTaken().getsubjectName());

Console.WriteLine("Teacher Name:" + t1.getName()); Console.WriteLine("Teacher Address:" + t1.getAddress()); Console.WriteLine("Teacher Phone:" + t1.getPhone()); Console.WriteLine("Teacher Subject Taught:" + t1.getSubjectTaught().getsubjectName()); Console.Read(); } }}

Output

Student Name:Sujatha

Student Address:Anandnagar

Student Phone:9885655627

Student USN:1AT02CS007

Student branch:CSE

Student Subject Taken:C#

Teacher Name:Seema

Teacher Address:Hebbal

Teacher Phone:080-765676

Teacher Subject Taught:C#

A C# property actually maps to a get_/set_ pair. (The reverse is not true)Eg:

public class Employee{

private string empSSN;public string SSN

{get { return empSSN;}set{ empSSN = value;}

}

//ERRORpublic string get_SSN()

{ return empSSN;}

public string set_SSN(string val){empsSN = val;}

}

Read-Only and Write-Only properties

• To configure a read-only property, simply build a property without a corresponding set block.

• If you wish to have write-only property, omit the get block.

public class Employee{

private string empSSN;public Employee(string FullName, int empID, float currPay, string ssn){

this.fullName = FullName;this.empID = empID;this.currPay = currPay;this.empSSN = ssn;

}public string SSN { get { return empSSN;}}

}

Static properties

public class Employee{

private static string companyName;

public static string Company{

get { return companyName;}set { companyName = value;}

}

//Usage: Employee.Company = “Infosys Inc”;Console.WriteLine(“The folks work at {0}”, Employee.Company);

Static Constructor

• Static constructors can be used to assign values to static data• This assignment always happens by default.

public class Employee{

private static string companyName;static Employee(){

companyName = “Infosys Inc”;}

}//UsageConsole.WriteLine (“These folks work at {0}”, Employee.Company);

Read-Only fields (Psudo encapsulation)

public class Employee{

public readonly string SSNField;public Employee(string FullName, int empID, float currPay, string ssn){

this.fullName = FullName;this.empID = empID;this.currPay = currPay;this.empSSN = ssn;this.SSNField = ssn;

}}

//ErrorEmployee brenner = new Employee();brenner.SSNField = “666-66-666”;

Preventing Inheritance

public sealed class PTSalesPerson : SalesPerson

{

Public PTSalesPerson(string fullName, int empID, float currPay, string ssn, int numberOfSales)

{

//Logic

}

}

//Error

Public class ReallyPTSalesPerson: PTSalesPerson

Containment and Delegation (has-a) relationship

• Eg: Car, radio

Nested Type Definitions public class Car{

private class Radio{

public void TurnOn(bool on){

if (on) Console.WriteLine(“Jamming…”);

elseConsole.WriteLine(“Quiet Time…”);

}}private Radio theMusicBox = new Radio();

}

• Nested type could be public or private (Not true for other types)• Car$Radio

C# Polymorphic supportpublic class Employee

{

protected string fullName;

protected int empID;

protected float currPay;

protected string empSSN;

public Employee(string FullName, int empID, float currPay, string ssn)

{

this.fullName = FullName;

this.empID = empID;

this.currPay = currPay;

this.empSSN = ssn;

}

public void GiveBonus(float amount)

{

currPay + = amount;

}

}

public class SalesPerson : Employee{

protected int numberOfSales;

public SalesPerson(string FullName, int empID, float currPay, string ssn, int numbOfSales)

: base(FullName, empID, currPay, ssn){

numberOfSales = numbOfSales;}

}

public class Manager : Employee{

private ulong numberOfOptions;

public Manager(string FullName, int empID,

float currPay, string ssn, ulong numbOfOpts)

: base(FullName, empID, currPay, ssn)

{

// This point of data belongs with us!

numberOfOptions = numbOfOpts;

}

}

Manager Chucky = new Manager(“Chucky”, 92, 10000, “333-33-3333”, 9000);

Chucky.GiveBonus();

SalesPerson fran= new Manager(“Fran”, 93, 3000, “999-99-9999”, 31);

Chucky.GiveBonus();

public class Employee

{

protected string fullName;

protected int empID;

protected float currPay;

protected string empSSN;

public Employee(string FullName, int empID, float currPay, string ssn)

{

this.fullName = FullName;

this.empID = empID;

this.currPay = currPay;

this.empSSN = ssn;

}

public virtual void GiveBonus(float amount)

{

currPay + = amount;

}

}

public class SalesPerson : Employee{

protected int numberOfSales;

public SalesPerson(string FullName, int empID, float currPay, string ssn, int numbOfSales)

: base(FullName, empID, currPay, ssn){

numberOfSales = numbOfSales;}public override void GiveBonus(float amount){

int salesBonus = 0;

if(numberOfSales >= 0 && numberOfSales <= 100) salesBonus = 10;

else if(numberOfSales >= 101 && numberOfSales <= 200)salesBonus = 15;

elsesalesBonus = 20; // Anything greater than

200.

base.GiveBonus(amount * salesBonus);}

}

public class Manager : Employee

{

private ulong numberOfOptions;

public Manager(string FullName, int empID,

float currPay, string ssn, ulong numbOfOpts)

: base(FullName, empID, currPay, ssn)

{

// This point of data belongs with us!

numberOfOptions = numbOfOpts;

}

public override void GiveBonus(float amount)

{

// Increase salary.

base.GiveBonus(amount);

// And give some new stock options...

Random r = new Random();

numberOfOptions += (ulong)r.Next(500);

}

}

Manager Chucky = new Manager(“Chucky”, 92, 10000, “333-33-3333”, 9000);

Chucky.GiveBonus(300);

SalesPerson fran= new Manager(“Fran”, 93, 3000, “999-99-9999”, 31);

Chucky.GiveBonus(200);

abstract Classes and abstract methods• You can directly create instances of Employee• This is rather odd.• Better design would be to prevent the ability to directly

create a new Employee instance. • Once a class is abstract, it may contain any number of

abstract methods• Abstract methods can be used when a method is to be

defined that does not supply a default implementation.

abstract public class Employee{

//Logic}

Object

Shape

Hexagon

Circle

Void Draw()

Draw()

Draw()

namespace Shapes{

public abstract class Shape{

protected string petName;

// Constructors.public Shape(){petName = "NoName";}public Shape(string s){

this.petName = s;}

public virtual void Draw(){

Console.WriteLine(“Shape.Draw”);}

public string PetName{

get {return this.petName;}set {this.petName = value;}

}}

public class Circle : Shape

{

public Circle(){}

// Call base class constructor.

public Circle(string name): base(name){}

// Circle does not override draw

}

public class Hexagon : Shape{

public Hexagon(){}public Hexagon(string name): base(name){}

public override void Draw(){Console.WriteLine("Drawing " + PetName + " the

Hexagon");}

}

public class ShapesApp{ public static int Main(string[] args) {

// The C# base class pointer trick.Shape[] s = {new Hexagon(), new Circle(), new Hexagon("Mick"),

new Circle("Beth"), new Hexagon("Linda")};

for(int i = 0; i < s.Length; i++){

s[i].Draw();}

}}

namespace Shapes{

public abstract class Shape{

protected string petName;

// Constructors.public Shape(){petName = "NoName";}public Shape(string s){

this.petName = s;}

public abstract void Draw();

public string PetName{

get {return this.petName;}set {this.petName = value;}

}}

public class Circle : Shape

{

public Circle(){}

// Call base class constructor.

public Circle(string name): base(name){}

public override void Draw()

{

Console.WriteLine("Drawing " + PetName + " the Circle");

}

}

public class Hexagon : Shape{

public Hexagon(){}public Hexagon(string name): base(name){}

public override void Draw(){Console.WriteLine("Drawing " + PetName + " the

Hexagon");}

}

public class ShapesApp{ public static int Main(string[] args) {

// The C# base class pointer trick.Shape[] s = {new Hexagon(), new Circle(), new Hexagon("Mick"),

new Circle("Beth"), new Hexagon("Linda")};

for(int i = 0; i < s.Length; i++){

s[i].Draw();}

}}

Versioning• C# allows derived classes to contain methods with the same name as base

class methods.

• The base class method must be defined virtual.

• If the method in the derived class is not preceded by new or override keywords, the compiler will issue a warning and the method will behave as if the new keyword were present.

• If the method in the derived class is preceded with the new keyword, the method is defined as being independent of the method in the base class.

• If the method in the derived class is preceded with the override keyword, objects of the derived class will call that method rather than the base class method.

• The base class method can be called from within the derived class using the base keyword.

• The override, virtual, and new keywords can also be applied to properties, indexers, and events.

public class MyBase { public virtual string Meth1() { return "MyBase-Meth1"; } public virtual string Meth2() { return "MyBase-Meth2"; } public virtual string Meth3() { return "MyBase-Meth3"; }}

Versioning

class MyDerived : MyBase { // Overrides the virtual method Meth1 using the override keyword: public override string Meth1() { return "MyDerived-Meth1"; }

// Explicitly hide the virtual method Meth2 using the new keyword public new string Meth2() { return "MyDerived-Meth2"; }

// Because no keyword is specified in the following declaration // a warning will be issued to alert the programmer that // the method hides the inherited member MyBase.Meth3(): public string Meth3() { return "MyDerived-Meth3"; }

public static void Main() { MyDerived mD = new MyDerived(); MyBase mB = (MyBase) mD;

System.Console.WriteLine(mB.Meth1()); System.Console.WriteLine(mB.Meth2()); System.Console.WriteLine(mB.Meth3());}

Output

MyDerived-Meth1 MyBase-Meth2 MyBase-Meth3

Casting between Types

• Implicit cast operations

• //Manager “is-a” object• Object frank = new Manager(“Frank”, 9, 40000, “111-11-1111”, 5);

• //Manager “is-a” Employee• Employee moonunit= new Manager(“MoonUnit”, 9, 40000, “111-15-1111”,

5);

• //PTSalesPerson is a SalesPerson• SalesPerson jill = new PTSalesPerson(“Jill”, 834, 4000, “145-11-1111”, 5);

• First law of Casting: • When two classes are related by a “is-a” relationship, it is always safe

to reference a derived class using a base class reference.

public class TheMachine(){

Public static void FireThisPerson(Employee e){

//Remove from database//Get key and pencil sharpener from fired Employee

}}

Employee moonunit= new Manager(“MoonUnit”, 9, 40000, “111-15-1111”, 5);TheMachine.FireThisPerson(moonunit);

SalesPerson jill = new PTSalesPerson(“Jill”, 834, 4000, “145-11-1111”, 5);TheMachine.FireThisPerson(jill)

Object frank = new Manager(“Frank”, 9, 40000, “111-11-1111”, 5);TheMachine.FireThisPerson(frank); //Error

You cannot treat a base type reference as a derived type without first performing an explicit cast !

TheMachine.FireThisPerson((Employee)frank);

Determining the Type of Employee

public class TheMachine{

public static void FireThisPerson(Employee e){

if (e is SalesPerson){Console.WriteLine(“Lost a salesperson names {0}”, e.getfullName());Console.WriteLine(“{0} made {1} sales…”, e.GetFullName,

((SalesPerson)e).NumbSales);}

if (e is Manager){Console.WriteLine(“Lost a Manager names {0}”, e.getfullName());Console.WriteLine(“{0} had {1} stock options…”, e.GetFullName,

((Manager)e).NumbOpts);}

}}

public class TheMachine{

public static void FireThisPerson(Employee e){

SalesPerson p = e as SalesPerson;if (p != null){Console.WriteLine(“Lost a salesperson names {0}”, p.getfullName());Console.WriteLine(“{0} made {1} sales…”, p.getFullName(),

p.NumbSales);}else{

Manager m = e as Manager;if (m != null){

Console.WriteLine(“Lost a Manager names {0}”, m.getfullName());

Console.WriteLine(“{0} had {1} stock options…”, m.getFullName(), m.NumbOpts);

} } } }

Numerical casts

• int x = 30000;• byte b = (byte) x; //Loss of information, so cast explicitly

• byte b = 30;• int x = b; //No loss

1. The present population of two countries, namely My Country and Your Country are 817 million and 1.088 billion respectively. Their rates of population growth are 2.1% and 1.3% respectively. Write a C# program that determines the number of years until the population of My Country exceeds that of your country.

2. Enter two non-zero numbers. Write a program in C# to display the highest common factor and lowest common multiple.

3. Write a program to display the Fibonacci series up to N in C#.

4. Design a C# program to define a structure:

Student<USN, Name, Marks, Branch> Here, Branch is of type enum, with members <CSE, ISE, ELNS, EE, IT>.

Add Appropriate constructor and also a method to hike the marks by 10% to only CSE students. Show creation of some student objects and the way to call these methods.

1. When a class has a set of identically named members that differ by the return types, the method is said to be overloaded (True/False)

2. ________ keyword is used for self-reference in C#

3. All static members of a class can refer to themselves using the this keyword.

4. Point out the error in this code, if any.class Employee

{

int empID;

public Employee(int empID) { this.empID = empID;}

public Employee():this(007){}

}

5. What is a the default Public Interface of a Type?

6. A Type can have the visibility ___________ or _________

7. _____________ pillar of OOP lets you extend the behavior of a class.

8. What is Classical inheritance?

9. What is Classical Polymorphism?

10. Give one keyword in C# that enforces Encapsulation.

11. What are accessor and mutator functions?

12. Write a Property to provide readonly access this Datafield.

private int empID;

13. The Properties map to _____ and __________ methods.

14. A static constructor can be used to ___________________

15. How can read-only Fields be declared?

16. Multiple inheritance is supported by C# (True/False)

17. _________ keyword can be used to Prevent Inheritance.

18. __________ relationship is also known as Containment/Delegation model.

19. Nested Types can have visibility _________

20. A base class can enforce Polymorphism using the ________ keyword.

21. What are abstract classes?

22. ________ keyword is prefixed to a method is it needs to break its relationship with the base class.

23. _________ operators are used to determine the “type of” an object.

24. Numerical casts from smaller numerical type to higher numerical type should be explicit. (true/False)