Cukurova University Electrical-Electronics 9/19/2019 Eng ... · 9/1/2019 · A class is like a template, or cookie cutter You use the class’s constructor to make objects An Abstract

Cukurova University Electrical-Electronics Eng. Dept.

9/19/2019

EEES-403 Programming Languages (2019) 1

Basic Object-Oriented Concepts in C Sharp

Basic Object-Oriented Concepts◦ Class

◦ Inheritance

◦ Polymorphism

◦ Constructor

◦ Destructors

Early high-level languages are typically called procedural languages.

Procedural languages are characterized by sequential sets of linear commands. The focus of such languages is on structure.

Examples include C, Fortran, HTML, VBScript

Most object-oriented languages are high-level languages.

The focus of OOP languages is not on structure, but on modeling data.

Programmers code using “blueprints” of data models called classes.

Examples of OOP languages include C++, Visual Basic.NET and Java.

int main(){int x,y,z;int a,b,c;

a=f1(x);b=f2(y);c=f3(z);…

}

int f1(){}

int f2()

{}

int f3(){}

Class A{Int x;Int f1();}

Class B{Int y;Int f2()}

Class C{Int z;Int f3();}

int main(){A a;B b;C c;

a.f1();b.f2();c.f3();…

}

procedural programming:

a sequence of ‘procedures’


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Object – Unique programming entity that has methods, has attributes and can react to events.

Method – Things which an object can do; the “verbs” of objects. In code, usually can be identified by an “action” word -- Hide, Show

Attribute – Things which describe an object; the “adjectives” of objects. In code, usually can be identified by a “descriptive” word –Enabled, BackColor

Events – Forces external to an object to which that object can react. In code, usually attached to an event procedure

Class – Provides a way to create new objects based on a “meta-definition” of an object (Example: The automobile class)

Constructors – Special methods used to create new instances of a class (Example: A Honda Civic is an instance of the automobile class.)

Incorporation into a class of data & operations in one package

Data can only be accessed through that package

“Information Hiding”

Allows programmers to create new classes based on an existing class

Methods and attributes from the parent class are inherited by the newly-created class

New methods and attributes can be created in the new class, but don’t affect the parent class’s definition

Creating methods which describe the way to do some general function (Example: The “drive” method in the automobile class)

Polymorphic methods can adapt to specific types of objects.


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A class is a data type that allows programmers

to create objects. A class provides a definition for an object, describing an object’s attributes (data) and methods (operations).

An object is an instance of a class. With one class, you can have as many objects as required.

This is analogous to a variable and a data type, the class is the data type and the object is the variable.

In old style programming, you had:◦ data, which was completely passive

◦ functions, which could manipulate any data

An object contains both data and methods that manipulate that data◦ An object is active, not passive; it does things

◦ An object is responsible for its own data

But: it can expose that data to other objects

An object contains both data and methods that manipulate that data◦ The data represent the state of the object

◦ Data can also describe the relationships between this object and other objects

Example: A Student might have◦ A grade (the internal state of the grade)

◦ An owner (some object representing a person)

You could (in a game, for example) create an object representing a rabbit

It would have data:◦ How hungry it is

◦ How frightened it is

◦ Where it is

And methods:◦ eat, hide, run, dig

Every object belongs to (is an instance of) a class

An object may have fields, or variables◦ The class describes those fields

An object may have methods◦ The class describes those methods

A class is like a template, or cookie cutter◦ You use the class’s constructor to make objects

An Abstract Data Type (ADT) bundles together:◦ some data, representing an object or "thing"

◦ the operations on that data

The operations defined by the ADT are the onlyoperations permitted on its data

Example: a Student, with operations grade, takingclasses, GPA, etc.

Classes enforce this bundling together◦ If all data values are private, a class can also enforce

the rule that its defined operations are the only ones permitted on the data


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class Temperature {

public:

double degree;

char scale;

};

a new (user-defined) type, a composite type: Temperature!

Two member variables: degree and scale

structure Temperature {

double degree;

char scale;

};

class Person {// Fields

{ private int Age; //Can get but not change

private string Name; // Cannot get or set// Methods

public void GetValues( int myAge, string myName)

{ Age = myAge; Name = myName; }public int DateOfBirth() { return 2019 - Age; } // getter

}

class Employee {// Fields

private String name; //Can get but not change

private double salary; // Cannot get or set// Constructor

Employee(String n, double s)

{name = n;

salary = s;

}// Methods

void pay () {

Console.WriteLine("Pay to the order of " + name + " $" + salary);}

public String getName() { return name; } // getter

}

class Person

{ private int Age;

private string Name;

public void GetValues( int myAge, string myName)

{ Age = myAge; Name = myName; }

public int DateOfBirth() { return 2019 - Age; }

}

.......

Person student; // declares student

student = new Person (); // allocates space

Person student = new Person(); // does both

But the student is still "blank" (null)

student.GetValues(20, "Ayse"); // Send a message

int year = student.DateOfBirth(); // sends a message

int Age; does two things:◦ It declares that Age is an integer variable◦ It allocates space to hold a value for Age

◦ For a primitive, this is all that is needed

Person student; also does two things◦ It declares that student is type Person◦ It allocates space to hold a reference to an Person

◦ For an object, this is not all that is needed

student = new Person ( );◦ This allocate space to hold a value for the Person◦ Until you do this, the Employee is null

temp1.degree=54.0;

temp1.scale=‘F’;

temp2.degree=104.5;

temp2.scale=‘C’;

Temperature temp1, temp2;

The modifier ‘public’ means that the member variables can be accessed from the objects


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instance = object

field = instance variable

method = function

sending a message to an object = calling a function

These are all approximately true

Classes are arranged in a treelike structure called a hierarchy

The class at the root is named Object

Every class, except Object, has a superclass

A class may have several ancestors, up to Object

When you define a class, you specify its superclass◦ If you don’t specify a superclass, Object is assumed

Every class may have one or more subclasses

A FileDialog is a Dialog is a Window is a Container

Container

Panel ScrollPane Window

Dialog Frame

FileDialog

Inheritance allows a software developer to derive a new class from an existing one.

The existing class is called the parent, super, or base class.

The derived class is called a child or subclass.

The child inherits characteristics of the parent.◦ Methods and data defined for the parent class.

The child has special rights to the parents methods and data.

The child has its own unique behaviors and data.

Inheritance relationships are often shown graphically in a classdiagram, with the arrow pointing to the parent class.

Inheritance should create an is-a relationship, meaning the child is amore specific version of the parent.

Animal

Bird

Base c lass Derived c lasses

Student GraduateStudent

UndergraduateStudent

Shape Circle

Triangle

Rectangle

Loan CarLoan

HomeImprovementLoan MortgageLoan

Employee FacultyMember StaffMember

Account CheckingAccount

SavingsAccount


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Define a new class DerivedClass which extends BaseClass

class BaseClass

{

// class contents

}

class DerivedClass : BaseClass

{

// class contents

}

class CurrentAccount : BankAccount{

private int overdraftFacility;

public CurrentAccount(int n, string name, int b, int ov) : base(n, name, b) {

overdraftFacility = ov; }

public override void withdraw(int amount) {

if (base.Balance - amount > -overdraftFacility)base.Balance -= amount;

}}

class DepositAccount : BankAccount{

private float interestRate;

public DepositAccount(int n, string name, int b, float rate) : base( n, name,b) { interestRate = rate; }

float calcInterest() {

float interest = base.Balance * interestRate;base.Balance += (int)(interest);return interest;

} }

accountNumberaccountHolderbalance

deposit()withdraw()

overdraftFacility

withdraw()

interestRate

calcInterest()


deposit()withdraw()

CurrentAccount DepositAccount

Polymorphism is the key concept in object oriented programming

Polymorphism literally means many forms

Essentially we are able to get many different types of object behaviour from a single reference type◦ This enables us to write easily extensible applications

For example in a computer game that simulates the movement of animals we can send ‘move’ commands to different types of animal

We send the commands via an animal reference which is the base class for the different animal types

◦ But each type behaves differently once it receives the command

◦ Such an approach leads to a readily extendable application

animal Move

Application


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Polymorphism is implemented through references to objects

We can assign base class object references to any derived class object

BankAccount acc1 = new CurrentAccount(12345, "John Smith", 1000, 500);

BankAccount acc2 = new DepositAccount(54321, "Bill Jones", 2000, 5.0);

acc1

CurrentAccount

500

withdraw()

12345John Smith1000

deposit()withdraw()

acc2

DepositAccount

5.0

calcInterest()

54321Bill Jones2000

deposit()withdraw()

We can see that in the case of the reference to a CurrentAccountObject object, method withdraw() is overidden in the derived class

The question is, which one is called at runtime?

public class BankAccountTest{

static void Main(string[] args){

BankAccount acc1 = new CurrentAccount(12345, "John Smith“,1000, 500);

acc1.withdraw(250); // Which withdraw()?}

}


deposit()withdraw()

overdraftFacility

withdraw()

acc1

CurrentAccount

Which one

is called?

Instance constructors are special methods that are called when a class or struct is instantiated

Performs custom initialization Can be overloaded

If a class doesn’t define any constructors, an implicit parameterless constructor is created

Cannot create a parameterless constructor for a struct◦ All fields initialized to zero/null


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class addition{

int a, b;public addition() //default contructor{

a = 100;b = 175;

}

public static void Main(){

addition obj = new addition(); //an object is created , constructor is called

Console.WriteLine(obj.a);Console.WriteLine(obj.b);Console.Read();

}}

One constructor can call another with a constructor initializer

Use the this keyword. The called constructor will execute before the body of the current constructor.

class employee

{private string name;

private int age;public employee(employeeemp) // declaring Copy constructor.

{name = emp.name;

age = emp.age;}

public employee(stringname, int age) // Instance constructor.{

this.name = name;this.age = age;

}public string Details // Get deatils of employee

{return " The age of " + name +" is "+ age.ToString();

}}

45

A destructor is a method that is called before an instance is garbage collected

Used to clean up any resources held by the instance, do bookkeeping, etc.

Only classes, not structs can have destructors

class Program{

~Program() // destructor define {

// clean up statement}

}

C# destructors are non-deterministic

They are not guaranteed to be called at a specific time

They are guaranteed to be called before shutdown

You can not directly call the destructor

Slows down the garbage collection if you define one, so don’t unless you have to.


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Cukurova University Electrical-Electronics 9/19/2019 Eng ... · 9/1/2019 · A class is like a template, or cookie cutter You use the class’s constructor to make objects An Abstract