Difference between Interface and Abstract Class In C# ?

Interface	Abstract Class
Interface Keyword is given before the name of the Interface                 public interface IAbc         {             ////         }	Abstract keyword is used before the name  of the class        public abstract class Abc         {             ////   }
Only method declarations must be in  the interface (No fields, no properties in the interface)        public interface IAbc         {             public void Method1();             public void Method2();             public string Method3();             protected int Method4();         }	Atleast one or more abstract methods must be in the abstract class (or) All the methods may be abstract and fields, properties, delegates can be declared in abstract class  public abstract class Abc   {      public abstract void Method1();      public void Method2()      {        Console.WriteLine("I am Method2");      }      protected abstract string Method3();      public int Method4()       {           int a=10;           int b=20;          return (a + b);        }    }
By default methods declarations in interface are public. We can declare public or protected in interface.	By default methods in a class or abstract class are private. We can declare public or protected abstract classes.
All the method declarations in interface must be implemented in derived class. class Xyz : IAbc  {    public void Method1()     {        Console.WriteLine("I am  Method1");      }    public void Method2()     {       Console.WriteLine("I am Method2");     }     public string Method3()     {       string a = "Koding Attitude";       return a;     }     protected int Method4()      {        int a=10;        int b=20;       return (a + b);      }   }	The abstract methods may or may not be implemented in derived class i.e., only necessary abstract methods can be implemented. class Xyz : Abc  {    public override void Method1()     {                 Console.WriteLine("Overrided Abstract Method1");     }  protected override void Method3()   {                 Console.WriteLine("Overrided Abstract Method3");   }  }
An interface cannot be inherited from a class. Actually interface name starts with ‘I’, but it is not mandatory.	An abstract class can be inherited from a class, but we cannot create instance for abstract class.
We cannot create instance for interface, but we can create reference to the interface by using child class reference object. class Pqr  {       IAbc obj = new Xyz();        obj.Method1();  }	Even though abstract class can have constructor, it is not possible to create instance for abstract class, As abstract class is having partial implementation