Abstract Class

What?

An abstract class is an incomplete class or special class we can't be instantiated. The purpose of an abstract class is to provide a blueprint for derived classes and set some rules what the derived classes must implement when they inherit an abstract class.

The purpose of an abstract class is to provide a common definition of the base class that multiple derived classes can share and can be used only as a base class and never want to create the object of this class. Any class can be converted into an abstract class by adding the abstract modifier to it.

We can use an abstract class as a base class and all derived classes must implement abstract definitions. An abstract method must be implemented in all non-abstract classes using the override keyword. After overriding the abstract method is in the non-Abstract class. We can derive this class in another class and again we can override the same abstract method with it.

C# Abstract Class Features

• An abstract class can inherit from a class and one or more interfaces.
• An abstract class can implement code with non-Abstract methods.
• An Abstract class can have modifiers for methods, properties etc.
• An Abstract class can have constants and fields.
• An abstract class can implement a property.
• An abstract class can have constructors or destructors.
• An abstract class cannot be inherited from by structures.
• An abstract class cannot support multiple inheritance.

Example

abstract class Demo
    {
        public int Int1 { get; set; } //Non Abstract property  

        public abstract int Int2  //Abstract Property  
        {
            get;
            set;
        }

        public Demo()  //Constructor  
        {
            Console.WriteLine("Demo Constructor");
        }

        public void Method1()   //Non Abstract Method  
        {
            Console.WriteLine("Demo Method1");
        }

        public abstract void Method2();  //Abstract Method  

        ~Demo()  //Destructor  
        {
            Console.WriteLine("Demo Destructor");
        }

    }

    class Drived : Demo
    {
        public int Val;
        public override int Int2
        {
            get
            {
                return Val;
            }
            set
            {
                Val = value;
            }
        }

        public override void Method2()
        {
            Console.WriteLine("Drived Method2");
        }
    }
    class Program
    {
        static unsafe void Main(string[] args)
        {

            Drived Dr = new Drived();
            Dr.Int1 = 10;
            Dr.Int2 = 20;
            Dr.Method1();
            Dr.Method2();
            Console.ReadLine();
        }

    }