OOPs Difference FAQs-3

1.Difference between Abstraction and Encapsulation

S.No	Abstraction	Encapsulation
1	Abstraction solves the problem in the design level.	Encapsulation solves the problem in the implementation level.
2	Abstraction is used for hiding the unwanted data and giving relevant data.	Encapsulation means hiding the code and data into a single unit to protect the data from outside world.
3	Abstraction allows us to focus on what the object does instead of how it does it	Encapsulation means hiding the internal details or mechanism of how an object does something.
4	Abstraction- Outer layout, used in terms of design. For Example:- Outer Look of a Mobile Phone, like it has a display screen and keypad buttons to dial a number.	Encapsulation- Inner layout, used in terms of implementation. For Example:- Inner Implementation detail of a Mobile Phone, how keypad button and Display Screen are connected with each other using circuits

2.Difference between Composition and Aggregation

S.No	Composition	Aggregation
1	Defines a strongly-coupled relationship between two entities, where the one entity is part of another, and both need each other for their existence.	Defines a weakly-coupled relationship between two entities, where one entity could be part of another, but either can exist without the other, independantly.
2	e.g. Human body and the Heart.	e.g.School and teacher.
3	Composition implies real ownership of its components	Aggregation does not necessarily own any of its aggregates.
4	Composition has a stronger bond of its components.	Aggregation has weaker or looser bonds with its aggregates.
5	Composition has components that exist at the inner level.	Aggregation has aggregates that live at the outer level.

3.Difference between Private Class and Sealed Class

S.No	Private Class	Sealed Class
1	A Private class can only be accessed by the class it is defined and contain within - it is completely inaccessible to outside classes.	A Sealed class can be accessed by any class.Private Constructor of a Private Class = Sealed Class.
2	In private Class,we can create a constructor and therefore we can create an instance of that class.	In Sealed class we can not create a constructor of that class, so no instance of that class is possible.
3	The main use of Private class is to create a user-defined type, which we want to be accessible to that class only.	The sealed classes are mainly used to prevent inheritance features of object oriented programming.

Note: Private class(i.e private constructor) is also used to implement singleton classes(pattern). Singleton means "A single-instance object, and it simplify complex code. Singletons have a static property that we must access to get the object reference."

Example for Private Class:

public class A
  {
  private class B
     {
     }
  B b = new B();
  }
public class C
  {
  A.B b = new A.B(); // ERROR
  }

Example for Sealed Class:

public sealed class A
   {
   }
public class B : A //ERROR
   {
   }

4.Difference between Static Class and Sealed Class

S.No	Static Class	Sealed Class
1	We can neither create their instances, nor inherit them	We can create their instances, but cannot inherit them
2	They can have static members only.	They can contain static as well as nonstatic members.
3	Static classes are used when a class provides functionality that is not specific to any unique instance.	The sealed classes are mainly used to prevent inheritance features of object oriented programming.

Example for Static Class:

static class Program 
{ 

} 

Example for Sealed Class:

sealed class demo 
{ 

} 

class abc:demo 
{ 
--Wrong 
} 

5.Difference between Virtual method and Abstract method

S.No	Virtual method	Abstract method
1	Overriding : Virtual method may or may not override by inherited class. i.e.,Virtual method provide the derived class with the option of overriding it. Virtual = = Overridable	Overriding : An abstract method should be overriden by inherited class. i.e.,Abstract method forces the derived class to override it. abstract == MustOverride
2	Implementation: Virtual method has an implementation.	Implementation: Abstract method does not provide an implementation.
3	Necessity to Implement: Virtual methods allow subclasses to provide their own implementation of that method using the override keyword	Necessity to Implement: Abstract methods in a class contain no method body, and are implicitly virtual
4	Scope : Virtual methods scope to members only.	Scope : Abstract method's scope to members and classes
5	Instancing : Virtual methods - Not applicable, as we can't create instance for members, it is possible only with classes.	Instancing : Abstract method - directly NO, but other way,Yes.We can create an instance of a class that derives from an abstract class. And we can declare a type Abstract class and instantiate that as a derived class.

Example:

public abstract class Test

{

    public abstract void A();    // Abstract method

    public virtual void B()

    {  

        Console.WriteLine("Test.B"); } // Virtual Method

    }

        public class InheritedTest : Test

        {

            public override void A() 

            {

              Console.WriteLine("InheritedTest.A"); 

            }

            //Method B implementation is optional

            public override void B() 

            {

              Console.WriteLine("InheritedTest.B"); 

            }

        }

6.Difference between Class and Static Class

S.No	Class	Static Class
1	Class has Instance Members	Static class does not have Instance Members
2	In Class, Constructor has Access Specifier.	In Static Class, Constructor does not have Access Specifier.
3	In Class Constructor, initiation is done every time when an object is created for the class	In Static Class ,Constructor will be called only one time
4	In Class, Class members can be accessed through class object.	In Static Class, members can be accessed through its Class name only

7.Difference between Method Overloading and Method overriding in C#

S.No	Method Overloading	Method Overriding
1	Method Overloading is passing same message for different functionality	Method Overriding is redifining parent class function to the child class
2	Method Overloading is between the same function name with the different signature	Method Overriding is between the same method.
3	Method Overloading does not check for the return type.	Method Overriding checks the return type.
4	Method Overloading takes place in the same class.	Method Overriding takes place between parent and child classes
5	Method Overloading is static binding	Method Overriding is a dynamic binding.