OOPS
Concepts
Class:
It
is a collection of objects.
Object:
It
is a real time entity.
An
object can be considered a "thing" that can perform a set of related
activities. The set of activities that the object performs defines the
object's behavior. For example, the hand can grip something or a
Student (object) can give the name or address. In pure
OOP terms an object is an instance of a
class
The
above template describe about object Student
Class
is composed of three things name, attributes, and
operations
public
class student
{
}
student
objstudent=new student ();
According
to the above sample we can say that Student object, named objstudent,
has created out of the student class.
In
real world you will often find many individual objects all of the same kind. As
an example, there may be thousands of other bicycles in existence, all of the
same make and model. Each bicycle has built from the same blueprint. In
object-oriented terms, we say that the bicycle is an instance of the class of
objects known as bicycles. In the software world, though you may not have
realized it, you have already used classes. For example, the Textbox
control, you always used, is made out of the Textbox class,
which defines its appearance and capabilities. Each time you drag a
Textbox control, you are actually creating a new instance of the
Textbox class.
Encapsulation:
Encapsulation
is a process of binding the data members and member functions into a single
unit.
Example
for encapsulation is class. A class can contain data structures and
methods.
Consider
the following class
public
class Aperture
{
public
Aperture ()
{
}
protected
double height;
protected
double width;
protected
double thickness;
public
double get volume()
{
Double
volume=height * width * thickness;
if
(volume<0)
return
0;
return
volume;
}
}
In this example we encapsulate some data such as height, width, thickness and method Get Volume. Other methods or objects can interact with this object through methods that have public access modifier
Abstraction:
Abstraction
is a process of hiding the implementation details and displaying the essential
features.
Example1:
A Laptop consists of many things such as processor, motherboard, RAM, keyboard,
LCD screen, wireless antenna, web camera, usb ports, battery, speakers etc. To
use it, you don't need to know how internally LCD screens, keyboard, web camera,
battery, wireless antenna, speaker’s works. You just need to know how to
operate the laptop by switching it on. Think about if you would have to call to
the engineer who knows all internal details of the laptop before operating it.
This would have highly expensive as well as not easy to use everywhere by
everyone.
So
here the Laptop is an object that is designed to hide its
complexity.
How
to abstract: - By using Access Specifiers
.Net
has five access Specifiers
Public
-- Accessible outside the class through object
reference.
Private
-- Accessible inside the class only through member
functions.
Protected
-- Just like private but Accessible in derived classes also through
member
functions.
Internal
--
Visible inside the assembly. Accessible through objects.
Protected
Internal
-- Visible inside the assembly through objects and in derived classes outside
the assembly through member functions.
Let’s
try to understand by a practical example:-
public
class Class1
{
int i;
//No Access specifier means
private
public int
j; //
Public
protected int
k; //Protected
data
internal int
m; // Internal means visible
inside assembly
protected internal int
n; //inside assembly as well as to
derived classes outside assembly
static int
x; // This is also
private
public static
int y; //Static means shared across
objects
[DllImport("MyDll.dll")]
public static
extern int
MyFoo(); //extern means declared in this
assembly defined in some other assembly
public void
myFoo2()
{
//Within a class if you create an object of same
class then you can access all data members through object reference even private
data too
Class1 obj = new Class1();
obj.i =10; //Error can’t access private data
through object.But here it is accessible.:)
obj.j =10;
obj.k=10;
obj.m=10;
obj.n=10;
// obj.s =10; //Errror Static data can be
accessed by class names only
Class1.x = 10;
// obj.y = 10; //Errror Static data can be accessed
by class names only
Class1.y = 10;
}
}
Now
lets try to copy the same code inside Main
method and try to
compile
[STAThread]
static void
Main()
{
//Access specifiers comes into picture only when you
create object of class outside the class
Class1 obj = new
Class1();
// obj.i =10; //Error can’t access private data
through object.
obj.j =10;
// obj.k=10; //Error can’t access protected
data through object.
obj.m=10;
obj.n=10;
// obj.s =10; //Errror Static data can be
accessed by class names only
Class1.x = 10; //Error can’t access private data
outside class
// obj.y = 10; //Errror Static data can be accessed
by class names only
Class1.y = 10;
}
What
if Main is
inside another assembly
[STAThread]
static void
Main()
{
//Access specifiers comes into picture only when you
create object of class outside the class
Class1 obj = new
Class1();
// obj.i =10; //Error can’t access private data
through object.
obj.j =10;
// obj.k=10; //Error can’t access protected
data through object.
// obj.m=10; // Error can’t access internal data
outside assembly
// obj.n=10; // Error can’t access internal data
outside assembly
// obj.s =10; //Errror Static data can be
accessed by class names only
Class1.x = 10; //Error can’t access private data
outside class
// obj.y = 10; //Errror Static data can be accessed
by class names only
Class1.y = 10;
}
In
object-oriented software, complexity is managed by using abstraction.
Abstraction
is a process that involves identifying the critical behavior of an object and
eliminating irrelevant and complex details.
Inheritance:
Inheritance
is a process of deriving the new class from already existing
class
C#
is a complete object oriented programming language. Inheritance is one of the
primary concepts of object-oriented programming. It allows you to reuse existing
code. Through effective use of inheritance, you can save lot of time in your
programming and also reduce errors, which in turn will increase the quality of
work and productivity. A simple example to understand inheritance in C#.
Using
System;
Public
class BaseClass
{
Public BaseClass ()
{
Console.WriteLine ("Base Class Constructor executed");
}
Public void
Write ()
{
Console.WriteLine ("Write method in Base Class
executed");
}
}
Public
class ChildClass: BaseClass
{
Public ChildClass ()
{
Console.WriteLine("Child Class Constructor executed");
}
Public static void Main
()
{
ChildClass CC = new ChildClass
();
CC.Write ();
}
}
In
the Main () method in ChildClass we create an instance of childclass. Then we
call the write () method. If you observe the ChildClass does not have a write()
method in it. This write () method has been inherited from the parent BaseClass.
The
output of the above program is
Output:
Output:
Base Class Constructor executed
Child Class Constructor executed
Write method in Base Class executed
Child Class Constructor executed
Write method in Base Class executed
this
output proves that when we create an instance of a child class, the base class
constructor will automatically be called before the child class constructor. So
in general Base classes are automatically instantiated before derived classes.
In
C# the syntax for specifying BaseClass and ChildClass relationship is shown
below. The base class is specified by adding a colon, ":", after the derived
class identifier and then specifying the base class
name.
Syntax:
class ChildClassName: BaseClass
{
//Body
}
{
//Body
}
C#
supports single class inheritance only. What this means is, your class can
inherit from only one base class at a time. In the code snippet below, class C
is trying to inherit from Class A and B at the same time. This is not allowed in
C#. This will lead to a compile time
error:
Class 'C' cannot have multiple base classes: 'A' and 'B'.
public
class A
{
}
public
class B
{
}
public
class C :
A, B
{
}
In
C# Multi-Level inheritance is possible. Code snippet below demonstrates
mlti-level inheritance. Class B is derived from Class A. Class C is derived from
Class B. So class C, will have access to all members present in both Class A and
Class B. As a result of multi-level inheritance Class has access to
A_Method(),B_Method() and C_Method().
Note: Classes can inherit from multiple interfaces at the same time. Interview Question: How can you implement multiple inheritance in C#? Ans : Using Interfaces. We will talk about interfaces in our later article.
Note: Classes can inherit from multiple interfaces at the same time. Interview Question: How can you implement multiple inheritance in C#? Ans : Using Interfaces. We will talk about interfaces in our later article.
Using
System;
Public
class A
{
Public void
A_Method ()
{
Console.WriteLine ("Class A Method Called");
}
}
Public
class B:
A
{
Public void
B_Method ()
{
Console.WriteLine ("Class A Method Called");
}
}
Public
class C:
B
{
Public void
C_Method ()
{
Console.WriteLine ("Class A Method Called");
}
Public static void Main
()
{
C C1 = new C
();
C1.A_Method ();
C1.B_Method ();
C1.C_Method ();
}
}
When
you derive a class from a base class, the derived class will inherit all members
of the base class except constructors. In the code snippet below class B will
inherit both M1 and M2 from Class A, but you cannot access M2 because of the
private access modifier. Class members declared with a private access modifier
can be accessed only with in the class. We will talk about access modifiers in
our later article. Common
Interview Question:
Are private class members inherited to the derived
class?
Ans:
Yes, the private members are also inherited in the derived class but we will not
be able to access them. Trying to access a private base class member in the
derived class will report a compile time error.
Using
System;
Public
class A
{
Public
void M1 ()
{
}
Private
void M2 ()
{
}
}
Public
class B:
A
{
Public
static void
Main ()
{
B
B1 = new B
();
B1.M1
();
//Error,
Cannot access private member M2
//B1.M2
();
}
}
Method
Hiding and Inheritance We will look at an example of how to hide a method
in C#. The Parent class has a write () method which is available to the child
class. In the child class I have created a new write () method. So, now if I
create an instance of child class and call the write () method, the child class
write () method will be called. The child class is hiding the base class write
() method. This is called method hiding.
If we want to call the parent class write () method, we would have to type cast the child object to Parent type and then call the write () method as shown in the code snippet below.
If we want to call the parent class write () method, we would have to type cast the child object to Parent type and then call the write () method as shown in the code snippet below.
Using
System;
Public
class Parent
{
Public void
Write ()
{
Console.WriteLine ("Parent Class write method");
}
}
Public
class Child: Parent
{
Public new
void Write ()
{
Console.WriteLine ("Child Class write method");
}
Public static void Main
()
{
Child C1 = new Child
();
C1.Write ();
//Type caste C1 to be of type Parent and call
Write () method
((Parent) C1).Write ();
}
}
Polymorphism:
When
a message can be processed in different ways is called polymorphism.
Polymorphism means many forms.
Polymorphism
is one of the fundamental concepts of OOP.
Polymorphism
provides following features:
- It allows you to invoke methods of derived class through base class reference during runtime.
- It has the ability for classes to provide different implementations of methods that are called through the same name.
Polymorphism
is of two types:
- Compile time polymorphism/Overloading
- Runtime polymorphism/Overriding
Compile
Time Polymorphism
Compile
time polymorphism is method and operators overloading. It is also called early
binding.
In
method overloading method performs the different task at the different input
parameters.
Runtime
Time Polymorphism
Runtime
time polymorphism is done using inheritance and virtual functions. Method
overriding is called runtime polymorphism. It is also called late binding.
When
overriding a method, you change the behavior of the method for the
derived class. Overloading a method simply involves having another
method with the same prototype.
Caution:
Don't
confused method overloading with method overriding, they are different,
unrelated concepts. But they sound similar.
Method
overloading has nothing to do with inheritance or virtual methods.
Following
are examples of methods having different overloads:
void
area(int side);
void
area(int l, int b);
void
area(float radius);
Practical
example of Method Overloading (Compile Time Polymorphism)
using
System;
namespace
method_overloading
{
class Program
{
public class
Print
{
public void
display(string name)
{
Console.WriteLine ("Your name is : " + name);
}
public void
display(int age, float marks)
{
Console.WriteLine ("Your age is : " + age);
Console.WriteLine ("Your marks are :" + marks);
}
}
static void
Main(string[] args)
{
Print obj = new Print ();
obj.display ("George");
obj.display (34, 76.50f);
Console.ReadLine ();
}
}
}
Note:
In
the code if you observe display method is called two times. Display method will
work according to the number of parameters and type of parameters.
When
and why to use method overloading
Use
method overloading in situation where you want a class to be able to do
something, but there is more than one possibility for what information is
supplied to the method that carries out the task.
You
should consider overloading a method when you for some reason need a couple of
methods that take different parameters, but conceptually do the same thing.
Method
overloading showing many forms.
using
System;
namespace
method_overloading_polymorphism
{
Class Program
{
Public class
Shape
{
Public void
Area (float r)
{
float a = (float)3.14 * r;
// here we have used function overload with 1
parameter.
Console.WriteLine ("Area of a circle: {0}",a);
}
Public void
Area(float l, float b)
{
float x = (float)l* b;
// here we have used function overload with 2
parameters.
Console.WriteLine ("Area of a rectangle: {0}",x);
}
public void
Area(float a, float b, float c)
{
float s = (float)(a*b*c)/2;
// here we have used function overload with 3
parameters.
Console.WriteLine ("Area of a circle: {0}", s);
}
}
Static void
Main (string[] args)
{
Shape ob = new Shape ();
ob.Area(2.0f);
ob.Area(20.0f,30.0f);
ob.Area(2.0f,3.0f,4.0f);
Console.ReadLine ();
}
}
}
Things
to keep in mind while method overloading
If
you use overload for method, there are couple of restrictions that the compiler
imposes.
The
rule is that overloads must be different in their signature, which means the
name and the number and type of parameters.
There
is no limit to how many overload of a method you can have. You simply declare
them in a class, just as if they were different methods that happened to have
the same name.
Method
Overriding:
Base class method has to be marked with virtual keyword and we can override it in derived class using override keyword.
Derived class method will completely overrides base class method i.e. when we refer base class object created by casting derived class object a method in derived class will be called.
Example:
// Base classpublic class BaseClass
{
public virtual void Method1()
{
Console.Write("Base Class Method");
}
}
// Derived class
public class DerivedClass : BaseClass
{
public override void Method1()
{
Console.Write("Derived Class Method");
}
}
// Using base and derived class
public class Sample
{
public void TestMethod()
{
// calling the overriden method
DerivedClass objDC = new DerivedClass();
objDC.Method1();
// calling the baesd class method
BaseClass objBC = (BaseClass)objDC;
objDC.Method1();
}
}
Output
---------------------
Derived Class Method
Derived Class Method
Constructors
and Destructors:
Classes
have complicated internal structures, including data and functions, object
initialization and cleanup for classes is much more complicated than it is for
simple data structures. Constructors and destructors are special member
functions of classes that are used to construct and destroy class objects.
Construction may involve memory allocation and initialization for objects.
Destruction may involve cleanup and deallocation of memory for
objects.
- Constructors and destructors do not have return types nor can they return values.
- References and pointers cannot be used on constructors and destructors because their addresses cannot be taken.
- Constructors cannot be declared with the keyword virtual.
- Constructors and destructors cannot be declared const, or volatile.
- Unions cannot contain class objects that have constructors or destructors.
Constructors and
destructors obey the same access rules as member functions. For example, if you
declare a constructor with protected access, only derived classes and friends
can use it to create class objects.
The compiler
automatically calls constructors when defining class objects and calls
destructors when class objects go out of scope. A constructor does not allocate
memory for the class object it’s this pointer refers to,
but may allocate storage for more objects than its class object refers to. If
memory allocation is required for objects, constructors can explicitly call the
new operator. During cleanup, a destructor may release
objects allocated by the corresponding constructor. To release objects, use the
delete operator.
class C
Example of Destructor
{
private int
x;
private int
y;
public C (int
i, int j)
{
x = i;
y = j;
}
public void
display ()
{
Console.WriteLine(x + "i+" + y);
}
}Example of Destructor
class
D
{
public D ()
{
// constructor
}
~D ()
{
// Destructor
}
}
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