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Virtual VS Override VS new Keyword in ASP.Net C#

Method Overriding vs Method Hiding -Virtual | Override | new Keyword

In this article, I’ll explain how virtual, override and new keywords are different from each other by taking some examples as give below.

The virtual keyword is used to modify a method, property, indexer, or events declared in the base class and allow it to be overridden in the derived class.

The override keyword is used to extend or modify a virtual/abstract method, property, indexer, or event of base class into derived class.

The new keyword is used to hide a method, property, indexer, or event of base class into derived class.

Virtual and Override keywords are used in method overriding concept while new keyword is used in method overloading concept.
Virtual and Override keywords are also called run-time polymorphism while new keyword is called compile-time polymorphism.

Virtual and Override keywords cause late binding while new keyword causes early binding.

Method Overriding (Virtual and Override Keyword) -
For overriding the base class method in derived class, you must have to declare base class method as virtual and derived class method as override.

Let’s see in the below example –
namespace ConsoleApplication1
{
    class ClassA
    {
        public virtual void TestMethod()
        {
            Console.WriteLine("ClassA::MethodA()");
        }
    }

    class ClassB : ClassA
    {
        public override void TestMethod()
        {
            Console.WriteLine("ClassB:TestMethod()");
        }
    }

    class ClassC : ClassB
    {
        public override void TestMethod()
        {
            Console.WriteLine("ClassC:TestMethod()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            ClassB b = new ClassB();
            b.TestMethod();
            // output --> "ClassB::TestMethod()"

            ClassC c = new ClassC();
            c.TestMethod();
            // output --> "ClassC::TestMethod()"

            Console.ReadLine();
        }
    }
}

Method Hiding (New keyword) – The new keyword is used to hide a method, property, indexer, or event of base class into derived class.

Let’s see the example in detail -
namespace ConsoleApplication1
{
    class ClassA
    {
        public void TestMethod()
        {
            Console.WriteLine("ClassA::TestMethod()");
        }
    }

    class ClassB : ClassA
    {
        public new void TestMethod()
        {
            Console.WriteLine("ClassB:TestMethod()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            ClassA a1 = new ClassA();
            a1.TestMethod();
            //Output - ClassA::TestMethod()

            ClassB b1 = new ClassB();
            b1.TestMethod();
            //Output - ClassB::TestMethod()

            ClassA a2 = new ClassB();
            a2.TestMethod();
            //Output - ClassA::TestMethod()

            Console.ReadLine();
        }
    }
}

Other example for new Keyword –
namespace ConsoleApplication1
{
    class A
    {
        public void showMe()
        {
            Console.WriteLine("Base Class method - showMe!");
            Console.ReadLine();
        }
    }

    class B : A
    {
        public new void showMe()
        {
            Console.WriteLine("Derived Class method - showMe!");
            Console.ReadLine();
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            B a = new B();
            a.showMe(); //Output - Derived Class method - showMe!

            Console.ReadLine();
        }
    }
}

And
namespace ConsoleApplication1
{
    class A
    {
        public void showMe()
        {
            Console.WriteLine("Base Class method - showMe!");
            Console.ReadLine();
        }
    }

    class B : A
    {
        public void showMe() //Warning - Use the new keyword if hiding was intended.
        {
            Console.WriteLine("Derived Class method - showMe!");
            Console.ReadLine();
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            B a = new B();
            a.showMe(); //Output - Derived Class method - showMe!

            Console.ReadLine();
        }
    }
}

And other example –
namespace ConsoleApplication1
{
    class A
    {
        public void showMe()
        {
            Console.WriteLine("Base Class method - showMe!");
            Console.ReadLine();
        }
    }

    class B : A
    {
        public new void showMe()
        {
            Console.WriteLine("Derived Class method - showMe!");
            Console.ReadLine();
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            A a = new A();
            a.showMe(); //Output - Base Class method - showMe!

            B b = new B();
            b.showMe(); //Output - Derived Class method - showMe!

            a = new B();
            a.showMe();//Output - Base Class method - showMe!

            Console.ReadLine();
        }
    }
}

And other example –
namespace ConsoleApplication1
{
    class A
    {
        public virtual void showMe()
        {
            Console.WriteLine("Base Class method - showMe!");
            Console.ReadLine();
        }
    }

    class B : A
    {
        public new void showMe()
        {
            Console.WriteLine("Derived Class method - showMe!");
            Console.ReadLine();
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            A a = new A();
            a.showMe(); //Output - Base Class method - showMe!

            B b = new B();
            b.showMe(); //Output - Derived Class method - showMe!

            a = new B();
            a.showMe();//Output - Base Class method - showMe!

            Console.ReadLine();
        }
    }
}

Overloading examples –
namespace ConsoleApplication1
{
    class ClassA
    {
        public void TestMethod(int a)
        {
            Console.WriteLine("ClassA::TestMethod()");
        }
    }

    class ClassB : ClassA
    {
        public void TestMethod(ref int a)
        {
            Console.WriteLine("ClassB:TestMethod()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            //ClassB a = new ClassA();//Child class reference can't hold the parent class object.
            ClassA a=new ClassA();
            ClassA a1 = new ClassB();
            ClassB b = new ClassB();
            a.TestMethod(2); //Output - ClassA::TestMethod()
            a1.TestMethod(3); //Output - ClassA::TestMethod()
            b.TestMethod(4); //Output - ClassA::TestMethod()

            int x = 10;
            b.TestMethod(ref x); //Output - ClassB::TestMethod()

            Console.ReadLine();
        }
    }
}


Other examples are -







Inherited Methods
namespace ConsoleNamespace
{
    class ClassA
    {
        public void MethodA()
        {
            Console.WriteLine("A::MethodA()");
        }
    }

    class ClassB : ClassA { }

    class Test
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            a.MethodA(); 
            // output --> "A::MethodA()"

            ClassB b = new ClassB();
            b.MethodA(); 
            // output --> "A::MethodA()"
        }
    }
}

The method MethodA() can be overridden in classes ClassB and ClassC

//The method MethodA() can be overridden in classes ClassB and ClassC
namespace ConsoleNamespace
{
    class ClassA
    {
        public void MethodA()
        {
            Console.WriteLine("ClassA::MethodA()");
        }
    }

    class ClassB : ClassA
    {
        public void MethodA()
        {
            Console.WriteLine("ClassB:MethodA()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            ClassB b = new ClassB();
            a.MethodA();
            // output --> "ClassA::MethodA()"

            b.MethodA();
            // output --> "ClassB::MethodA()"

            a = new ClassB();
            a.MethodA();
            // output --> "ClassA::MethodA()"
        }
    }
}


Virtual and Overridden Methods

namespace ConsoleNamespace
{
    class ClassA
    {
        public virtual void MethodA()
        {
            Console.WriteLine("ClassA::MethodA()");
        }
    }

    class ClassB : ClassA
    {
        public override void MethodA()
        {
            Console.WriteLine("ClassB:MethodA()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            ClassB b = new ClassB();
            a.MethodA();
            // output --> "ClassA::MethodA()"

            b.MethodA();
            // output --> "ClassB::MethodA()"

            a = new ClassB();
            a.MethodA();
            // output --> "ClassB::MethodA()"

            Console.ReadLine();
        }
    }
}


Method Hiding

namespace ConsoleNamespace
{
    class ClassA
    {
        public virtual void MethodA()
        {
            Console.WriteLine("ClassA::MethodA()");
        }
    }

    class ClassB : ClassA
    {
        public new void MethodA()
        {
            Console.WriteLine("ClassB:MethodA()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            ClassB b = new ClassB();
            a.MethodA();
            // output --> "ClassA::MethodA()"

            b.MethodA();
            // output --> "ClassB::MethodA()"

            a = new ClassB();
            a.MethodA();
            // output --> "ClassB::MethodA()"

            Console.ReadLine();
        }
    }
}

Combining Method Overriding and Hiding

namespace ConsoleNamespace
{
    class ClassA
    {
        public void MethodA()
        {
            Console.WriteLine("ClassA::MethodA()");
        }
    }

    class ClassB : ClassA
    {
        public virtual new void MethodA()
        {
            Console.WriteLine("ClassB:MethodA()");
        }
    }

    class Test
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            ClassB b = new ClassB();
            a.MethodA();
            // output --> "ClassA::MethodA()"

            b.MethodA();
            // output --> "ClassB::MethodA()"

            a = new ClassB();
            a.MethodA();
            // output --> "ClassB::MethodA()"

            Console.ReadLine();
        }
    }
}



ANIL SINGH

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