A Tour of the C# Language

Key Take Aways

• Object oriented / component-oriented language
• Attributes that provide declarative info about the component; incorporate their own documentation
• The virtual keyword is used to modify a method, property, indexer, or event 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.

C# Inheritance

class A
{
public void Test() { Console.WriteLine("A::Test()"); }
}

class B : A { }

class C : A
{
public void Test() { Console.WriteLine("C::Test()"); }
}

B and C inherit method from A. If B or C implement the method in their class, it will override the implemented class A, as seen in class C.

Method Hiding

For hiding the base class method from derived class simply declare the derived class method with new keyword. Hence above code can be re-written as :

class A
{
public void Test() { Console.WriteLine("A::Test()"); }
}

class B : A
{
public new void Test() { Console.WriteLine("B::Test()"); }
}

class C : B {
public new void Test() { Console.WriteLine("C::Test()"); }
}

A a = new A();
B b = new B();
C c = new C();

a.Test(); // output --> "A::Test()"
b.Test(); // output --> "B::Test()"
c.Test(); // output --> "C::Test()"

a = new B();
a.Test(); // output --> "A::Test()"

b = new C();
b.Test(); // output --> "B::Test()"

Method Overriding

In C#, for overriding the base class method in derived class, you have to declare base class method as virtual and derived class method as override as shown below:

You can also mix the method hiding and method overriding by using virtual and new keyword since the method of a derived class can be virtual and new at the same time. This is required when you want to further override the derived class method into next level.

class A
{
public virtual void Test() { Console.WriteLine("A::Test()"); }
}

class B : A
{
public override void Test() { Console.WriteLine("B::Test()"); }
}

class C : B
{
public override void Test() { Console.WriteLine("C::Test()"); }
}

A a = new A();
B b = new B();
C c = new C();
a.Test(); // output --> "A::Test()"
b.Test(); // output --> "B::Test()"
c.Test(); // output --> "C::Test()"

a = new B();
a.Test(); // output --> "B::Test()"

b = new C();
b.Test(); // output --> "C::Test()"