Types of Classes in C# Concrete Class Abstract Class Partial Class Sealed Class Static Class Nested Class

1. TYPES OF CLASSES
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2. Definition:
 A class is a construct that enables you to create your own custom types by
grouping together variables of other types, methods and events.
 A class is like a blueprint. It defines the data and behavior of a type.
 When you define a class, you define a blueprint for a data type. This doesn't
actually define any data, but it does define what the class name means, that is,
what an object of the class will consist of and what operations can be
performed on such an object. Objects are instances of a class. The methods and
variables that constitute a class are called members of the class.
Declaration :
Classes are declared by using the class keyword, as shown in the following
example:
<access_specifier> class <class_name>
{
//Fields, properties, methods and events go here...
}
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3. Types of Classes
 Concrete Class
 Abstract Class
 Partial Class
 Sealed Class
 Static Class
 Nested Class
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4. Abstract Class
 An Abstract Class means that, no object of this class can be instantiated, but can
make derivation of this. It can serve the purpose of base class only as no object of
this class can be created.
Abstract Class is denoted by the keyword abstract.
 Use abstract when all sub-classes have to implement the method/property.
 Declaration of abstract class is :: abstract class absClass { }
 An abstract class can contain either abstract methods or non abstract methods.
Abstract members do not have any implementation in the abstract class, but the
same has to be provided in its derived class. Eg. of abstract methord —
abstract class absClass
{ public abstract void abstractMethod(); }
 Eg. of abstract class only with non abstract members.
abstract class absClass
{ public void NonAbstractMethod()
{ Console.WriteLine("NonAbstract Method"); } }
 An abstract class can be derived from another abstract class. In that case, in the
derived class, it is optional to implement the abstract method(s) of the base class.
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5. Example:
// Base abstract class
abstract class baseClass
{
public abstract int addNumbers (int a, int b);
public abstract int multiplyNumbers(int a, int b);
}
// Derived abstract class
abstract class derivedClass:baseClass
{
// implementing addNumbers…
public override int addnumbers (int a, int b)
{
return a+b;
}
}
// Derived class from 2nd class (derivedClass)
class anyClass: derivedClass
{
// implementing multiplyNumbers of baseClass…
public override int multiplyNumbers(int a, int b)
{
return a*b;
}
}
In the above example, we only implemented addNumbers in the derived abstract class (derivedClass). The
abstract method multiplyNumbers is implemented in the anyClass, which is in turn derived
from derivedClass.
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6. Partial Class
 This special type of class introduced with .Net Framework 2.0
 Partial Class allows its members – method, properties, and events
– to be divided into multiple source files.
 At compile time these files get combined into a single class.
 Partial Class is denoted by the keyword partial.
Do's and don'ts about partial class:-
• All the parts of a partial class must be prefixed with the keyword partial.
• Accessibility, signature etc. must be same in all parts of the partial class.
• You cannot seal one part of the partial class. In that case entire class in
sealed.
• If you define any part of the partial class abstract, entire class will
become abstract.
• Inheritance cannot be applied to a part of partial class. If you do so, it
applies to entire class.
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7. Example:
 public partial class myPartialClass
{
public void firstMethod()
{
// code…
}
}
public partial class myPartialClass
{
public void secondMethod()
{
// code…
}
}
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8. Sealed Class
 A sealed class is a class which cannot be inherited.
 A sealed class cannot be a base class.
 The modifier abstract cannot be applied to a sealed
class.
 To access the members of a sealed class, you must
create objects of that class.
 Sealed Class is denoted by the keyword sealed.
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9. Example:
sealed class mySealedClass
{
int a;
int b;
}
Class mainClass
{
public static void Main()
{
mySealedClass obj = new mySealedClass();
obj.a = 5;
obj.b = 7;
Console.WriteLine("a = {0}, b = {1}", obj.a,
obj.b);
}
}
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10. Static Class
A Static Class is one which cannot be instantiated. The keyword new cannot be
used with static classes as members of such class can be called directly by using
the class name itself.
It is a form of information hiding. You can use regular classes and
static classes in the same way, but the static modifier imposes an extra
restriction. The constructor is eliminated.
Static classes are loaded automatically by the .NET Framework
CLR when that program or namespace containing the class is
loaded.
Following are the main characteristics of a static class:-
•A Static Class can only have static members.
•A Static Class cannot be instantiated.
•A Static Class is sealed, so cannot be inherited.
•A Static Class cannot have a constructor (except static constructor).
Static Class is denoted by the keyword static.
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11. Example
 public static class Settings
{ static int i;
public static string GetName()
{ return "MyName"; }
}
class Program { static void Main(string[] args)
{ string str=Settings.GetName();
Console.Write(str);
Console.Read();
} }
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12. Nested Class
 Nested classes are classes within classes.
Eg--
class OurOuterClass
{
public static void Main()
{
System.Console.WriteLine("OurOuterClass");
}
class OurNestedClass { }
}
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13. Thank You
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