Introduction
This article explains the various behaviors of inheritance in various cases. Inheritance is the ability to create classes which inherits certain aspects from parent classes.
Objective
To understand inheritance and its behavior in various cases and to understand keywords like virtual, override, new and abstract.
CASE 1: What will happen when the virtual keyword is used with a method without implementation? For example:
CODE
class A
{
public virtual void Show();
}
RESULT
Error 1 'ConsoleApplication.A.Show()' must declare a body because it is not marked abstract, extern, or partial
CASE 2: What will happen when a method is used without implementation? For example:
CODE
class A
{
public void Show();
}
RESULT
Error 1 'ConsoleApplication.A.Show()' must declare a body because it is not marked abstract, extern, or partial
CASE 3: What will be the output of the C# .NET code snippet given below in which the base class method is overridden by a derived class using the override keyword?
CODE
class Program
{
static void Main(string[] args)
{
A obj = new B();
obj.Show();
Console.ReadLine();
}
}
class A
{
public virtual void Show()
{
Console.WriteLine("A.Show()");
}
}
class B : A
{
public override void Show()
{
Console.WriteLine("B.Show()");
}
}
RESULT
B.Show()
CASE 4: What will be the output of the C# .NET code snippet given below Where the base class method is overridden by a derived class using the new keyword?
CODE
class Program
{
static void Main(string[] args)
{
A obj = new B();
obj.Show();
Console.ReadLine();
}
}
class A
{
public virtual void Show()
{
Console.WriteLine("A.Show()");
}
}
class B : A
{
public new void Show()
{
Console.WriteLine("B.Show()");
}
}
RESULT
A.Show()
CASE 5: What will be the output of the C# .NET code snippet given below?
CODE
class Program
{
static void Main(string[] args)
{
A obj = new B();
obj.Show();
Console.ReadLine();
}
}
class A
{
public virtual void Show()
{
Console.WriteLine("A.Show()");
}
}
class B : A
{
public void Show()
{
Console.WriteLine("B.Show()");
}
}
RESULT
Warning 1 'ConsoleApplication.B.Show()' hides inherited member 'ConsoleApplication.A.Show()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
Output:
A.Show()
CASE 6: What happen when the abstract method is used with a non-abstract class?
CODE
class A
{
public abstract void Show()
{
Console.WriteLine("A.Show()");
}
}
RESULT
Error 1 'ConsoleApplication.A.Show()' cannot declare a body because it is marked abstract
Error 2 'ConsoleApplication.A.Show()' is abstract but it is contained in non-abstract class 'ConsoleApplication.A'
CASE 7: What will be the output of the C# .NET code snippet given below?
CODE
class Program
{
static void Main(string[] args)
{
C c = new C();
A a = new A();
a = c;
a.Show();
c.Show();
Console.ReadLine();
}
}
class A
{
public virtual void Show()
{
Console.WriteLine("A.Show()");
}
}
class B : A
{
public new void Show()
{
Console.WriteLine("B.Show()");
}
}
class C : B
{
public new void Show()
{
Console.WriteLine("C.Show()");
}
}
RESULT
A.Show()
C.Show()
CASE 8: What will be the output of the C# .NET code snippet given below?
CODE
class Program
{
static void Main(string[] args)
{
C c = new C();
A a = new A();
a = c;
a.Show();
c.Show();
Console.ReadLine();
}
}
class A
{
public virtual void Show()
{
Console.WriteLine("A.Show()");
}
}
class B : A
{
public override void Show()
{
Console.WriteLine("B.Show()");
}
}
class C : B
{
public new void Show()
{
Console.WriteLine("C.Show()");
}
}
RESULT
B.Show()
C.Show()
CASE 9: What will be the output of the C# .NET code snippet given below?
CODE
class Program
{
static void Main(string[] args)
{
C c = new C();
A a = new A();
a = c;
a.Show();
c.Show();
Console.ReadLine();
}
}
class A
{
public virtual void Show()
{
Console.WriteLine("A.Show()");
}
}
class B : A
{
public override void Show()
{
Console.WriteLine("B.Show()");
}
}
class C : B
{
public override void Show()
{
Console.WriteLine("C.Show()");
}
}
RESULT
C.Show()
C.Show()
CASE 10: What will be the output of the C# .NET code snippet given below?
CODE
class Program
{
static void Main(string[] args)
{
B b = new B(10);
Console.ReadLine();
}
}
class A
{
int i;
public A(int j)
{
i = j;
Console.WriteLine("Base");
}
}
class B : A
{
public B(int j)
{
Console.WriteLine("Derived");
}
}
RESULT
Error 1 'ConsoleApplication.A' does not contain a constructor that takes 0 arguments
CASE 11: What will be the output of the C# .NET code snippet given below?
CODE
class Program
{
static void Main(string[] args)
{
B b = new B(10);
Console.ReadLine();
}
}
class A
{
int i;
public A(int j)
{
i = j;
Console.WriteLine("Base");
}
}
class B : A
{
public B(int j)
: base(j)
{
Console.WriteLine("Derived");
}
}
RESULT
Base
Derived
Conclusion
Inheritance provides great reusability of the code.