Category: OOP

Introduction

Roadmap

Inheritance in Action

ClassA:

class ClassA
{

}

ClassB:

class ClassB
{
public int x = 100;
public void Display1()
{
Console.WriteLine(“ClassB Display1″);
}
public void Display2()
{
Console.WriteLine(“ClassB Display2″);
}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {

ClassA a = new ClassA();
a.Display1();
}
}

ClassA:

class ClassA:ClassB
{

}

ClassB:

class ClassB
{
public int x = 100;
public void Display1()
{
Console.WriteLine(“ClassB Display1″);
}
public void Display2()
{
Console.WriteLine(“ClassB Display2″);
}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            a.Display1();
            Console.ReadKey();
        }
    }

Output

ClassB Display1

class ClassA:ClassB
    {
        public void Display1()
        {
            System.Console.WriteLine("ClassA Display1");
        }
    }

ClassB:

class ClassB
{
public int x = 100;
public void Display1()
{
Console.WriteLine(“ClassB Display1″);
}
public void Display2()
{
Console.WriteLine(“ClassB Display2″);
}
}

class Program
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            a.Display1();
            Console.ReadKey();
        }
    }

ClassA Display1

ClassA:

class ClassA:ClassB
{
public void Display1()
{
Console.WriteLine(“ClassA Display1″);
base.Display1();
}
}

ClassB:

class ClassB
{
public int x = 100;
public void Display1()
{
Console.WriteLine(“ClassB Display1″);
}
public void Display2()
{
Console.WriteLine(“ClassB Display2″);
}
}

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            ClassA a = new ClassA();
            a.Display1();
            Console.ReadKey();
        }
    }

Output

ClassA Display1 
ClassB Display1

/// <summary>
   /// ClassB: acting as base class 
   /// </summary>
   class ClassB
    {
        public int x = 100;
        public void Display1()
        {
            Console.WriteLine("ClassB Display1");
        }
        public void Display2()
        {
            Console.WriteLine("ClassB Display2");
        }
    }

/// <summary>
/// ClassA: acting as derived class
/// </summary>
class ClassA : ClassB
{
public void Display1()
{
Console.WriteLine(“ClassA Display1″);
base.Display2();
}
}

/// <summary>
/// Program: used to execute the method.
/// Contains Main method.
/// </summary>
class Program
{
static void Main(string[] args)
{
ClassA a = new ClassA();
a.Display1();
Console.ReadKey();
}
}

Output

/// <summary>
   /// ClassB: acting as base class 
   /// </summary>
   class ClassB
    {
        public int x = 100;
        public void Display1()
        {
            Console.WriteLine("ClassB Display1");
        }
    }

/// <summary>
/// ClassA: acting as derived class
/// </summary>
class ClassA : ClassB
{
public void Display2()
{
Console.WriteLine(“ClassA Display2″);
}
}

/// <summary>
/// Program: used to execute the method.
/// Contains Main method.
/// </summary>
class Program
{
static void Main(string[] args)
{
ClassB b = new ClassB();
b.Display2();
Console.ReadKey();
}
}

Output

public class ClassB
    {
    }

public class ClassA : ClassB
{
}

public class ClassB:object
    {
    }

public class ClassA : ClassB
{
}

public class ClassW : System.ValueType
    {
    }

public class ClassX : System.Enum
{
}

public class ClassY : System.Delegate
{
}

public class ClassZ : System.Array
{
}

Errors

'InheritanceAndPolymorphism.ClassW' cannot derive from special class 'System.ValueType'
'InheritanceAndPolymorphism.ClassX' cannot derive from special class 'System.Enum'
'InheritanceAndPolymorphism.ClassY' cannot derive from special class 'System.Delegate'
'InheritanceAndPolymorphism.ClassZ' cannot derive from special class 'System.Array'

public class ClassW
    {
    }

public class ClassX
{
}

public class ClassY : ClassW, ClassX
{
}

public class ClassW:ClassY
    {
    }

public class ClassX:ClassW
{
}

public class ClassY : ClassX
{
}

Equalizing the Instances/Objects

ClassB:
public class ClassB
    {
        public int b = 100;
    }

ClassA:

public class ClassA
{
public int a = 100;
}

Program.cs

/// <summary>
    /// Program: used to execute the method.
    /// Contains Main method.
    /// </summary>
    public class Program
    {
        private static void Main(string[] args)
        {
            ClassB classB = new ClassB();
            ClassA classA = new ClassA();
            classA = classB;
            classB = classA;
        }
    }

Cannot implicitly convert type 'InheritanceAndPolymorphism.ClassB' to 'InheritanceAndPolymorphism.ClassA'

Cannot implicitly convert type ‘InheritanceAndPolymorphism.ClassA’ to ‘InheritanceAndPolymorphism.ClassB’

public class ClassB
    {
        public int a = 100;
    }

public class ClassA
{
public int a = 100;
}

public class ClassB
    {
        public int b = 100;
    }

public class ClassA:ClassB
{
public int a = 100;
}

/// <summary>
/// Program: used to execute the method.
/// Contains Main method.
/// </summary>
public class Program
{
private static void Main(string[] args)
{
ClassB classB = new ClassB();
ClassA classA = new ClassA();
classA = classB;
classB = classA;
}
}

Thus when we write classA = classB, classA looks like ClassA, ClassB and object and as a looks like ClassB, there is a match at ClassB.Result? No error  . Even though classB and classA have the same values, usingclassB we can only access the members of ClassB, even though had we used classA we could access ClassAalso. We have devalued the potency of classB. The error occurs at classA = classB, because the class ClassB is less/smaller than the class ClassA. The class ClassA has ClassB and more. We cannot have a larger class on the right and a smaller class on the left. classB only represents a ClassB whereas classA expects a ClassA which is aClassA andClassB.

public class ClassB
    {
        public int b = 100;
    }

public class ClassA:ClassB
{
public int a = 100;
}

/// <summary>
/// Program: used to execute the method.
/// Contains Main method.
/// </summary>
public class Program
{
private static void Main(string[] args)
{
ClassB classB = new ClassB();
ClassA classA = new ClassA();
classB=classA;
classA = (ClassA)classB;
}
}

public class ClassB
    {
        public int b = 100;
    }

public class ClassA // Removed ClassB as base class
{
public int a = 100;
}

/// <summary>
/// Program: used to execute the method.
/// Contains Main method.
/// </summary>
public class Program
{
private static void Main(string[] args)
{
ClassB classB = new ClassB();
ClassA classA = new ClassA();
classB = (ClassB)classA;
classA = (ClassA)classB;
}
}

Output

Cannot convert type 'InheritanceAndPolymorphism.ClassA' to 'InheritanceAndPolymorphism.ClassB'
Cannot convert type 'InheritanceAndPolymorphism.ClassB' to 'InheritanceAndPolymorphism.ClassA'

/// <summary>
    /// Program: used to execute the method.
    /// Contains Main method.
    /// </summary>
    public class Program
    {
        private static void Main(string[] args)
        {
            int integerA = 10;
            char characterB = 'A';
            integerA = characterB;
            characterB = integerA;
        }
    }

Output

Conclusion

1. No one can stop a derived class to have a method with the same name already declared in its base class.
2. Derived classes get a first chance at execution, then the base class.
3. A reserved keyword named “base” can be used in derived class to call the base class method.
4. Inheritance does not work backwards.
5. Except constructors and destructors, a class inherits everything from its base class.
6. In inheritance in C#, custom classes cannot derive from special built in C# classes like System.ValueType,System.Enum, System.Delegate, System.Array, etc.
7. A class can only be derived from one class in C#. C# does not support multiple inheritance by means of class.
8. Circular dependency is not allowed in inheritance in C#. ClassX is derived from ClassW which was derived from ClassY and ClassY was again derived from ClassX, which caused circular dependency in three classes, that is logically impossible.
9. We can only and only equate the dissimilar objects if they are derived from each other. We can equate an object of a base class to a derived class but not vice versa.
10. We cannot implicitly convert an int to char, but char can be converted to int.

Read more:

• C# and ASP.NET Questions (All in one)
• MVC Interview Questions
• C# and ASP.NET Interview Questions and Answers
• Web Services and Windows Services Interview Questions

Other Series

My other series of articles:

• Learning MVC
• Learning WebAPIs in .Net

For more informative articles visit my Blog.

Introduction

OOPS

1. What is OOPS and what is advantage of OOP?

2. What are OOP Concepts?

1. Data Abstraction: Data Abstraction is a concept in which the internal and superfluous details of the implementation of a logic is hidden from an end user(who is using the program) .A user can use any of the data and method from the class without knowing about how this is created or what is the complexity behind it. In terms of a real world example, when we drive a bike and change the gears we don’t have to care about how internally its working, like how liver is pulled or how chain is set.
2. Inheritance: Inheritance is most popular Concept in OOP’s .This provides a developer an advantage called reusability of code. Suppose a class is written having functions with specific logic, then we can derive that class into our newly created class and we don’t have to write the logic again for derived class functions, we can use them as it is.
3. Data Encapsulation: Wrapping up of member data and member functions of a class in a single unit is called encapsulation. The visibility of the member functions,data members is set via access modifiers used in class.
4. Polymorphism: Poly means many and morphism means many function The Concepts Introduces in the form of Many behaviours of an object.
5. Message Communication: Message Communication means when an object passes the call to method of class for execution.

1. Diving in OOP (Day 1): Polymorphism and Inheritance(Early Binding/Compile Time Polymorphism)
2. Diving in OOP (Day 2): Polymorphism and Inheritance (Inheritance)
3. Diving in OOP (Day 3): Polymorphism and Inheritance (Dynamic Binding/Run Time Polymorphism)
4. Diving in OOP (Day 4): Polymorphism and Inheritance (All about Abstarct classes in C#)
5. Diving in OOP (Day 5): All about access modifiers in C# (Public/Private/Protected/Internal/Sealed/Constants/Readonly Fields)
6. Diving in OOP (Day 6): Understanding Enum in C# (A Practical Approach)
7. Diving into OOP (Day 7): Properties in C# (A Practical Approach)
8. Diving into OOP (Day 8): Indexers in C# (A Practical Approach)
9. Diving into OOP (Day 9): Understanding Events in C# (An Insight)

3. Polymorphism:

Method Overloading or Early Binding or Compile Time Polymorphism

1. Let’s create a simple console application named InheritanceAndPolymorphism, and add a class namedOverload.cs and add three methods named DisplayOverload having varied parameters as follows,
   

   Overload.cs

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   public class Overload
       {
           public void DisplayOverload(int a){
               System.Console.WriteLine("DisplayOverload " + a);
           }
           public void DisplayOverload(string a){
               System.Console.WriteLine("DisplayOverload " + a);
           }
           public void DisplayOverload(string a, int b){
               System.Console.WriteLine("DisplayOverload " + a + b);
           }
       }

   In the main method in Program.cs file, add the following code,

   Program.cs

    Collapse | Copy Code

   class Program
       {
           static void Main(string[] args)
           {
               Overload overload = new Overload();
               overload.DisplayOverload(100);
               overload.DisplayOverload("method overloading");
               overload.DisplayOverload("method overloading", 100);
               Console.ReadKey();
           }
       }

Output

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public void DisplayOverload() { }
     public int DisplayOverload(){ }

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static void DisplayOverload(int a)  {   }
public void DisplayOverload(int a) {   }
public void DisplayOverload(string a){  }

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private void DisplayOverload(int a) {   }

private void DisplayOverload(out int a)
{
a = 100;
}

private void DisplayOverload(ref int a) { }

4. Role of Params Parameter in Polymorphism

1. pass by value,
2. Pass by reference,
3. As an output parameter,
4. Using parameter arrays.

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public void DisplayOverload(int a, string a)  {   }

public void Display(int a)
{
string a;
}

Overload.cs

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public class Overload
    {
        private string name = "Akhil";

public void Display()
{
Display2(ref name, ref name);
System.Console.WriteLine(name);
}

private void Display2(ref string x, ref string y)
{
System.Console.WriteLine(name);
x = “Akhil 1″;
System.Console.WriteLine(name);
y = “Akhil 2″;
System.Console.WriteLine(name);
name = “Akhil 3″;
}
}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Overload.cs

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public class Overload
    {
        public void Display()
        {
            DisplayOverload(100, "Akhil", "Mittal", "OOP");
            DisplayOverload(200, "Akhil");
            DisplayOverload(300);
        }

private void DisplayOverload(int a, params string[] parameterArray)
{
foreach (string str in parameterArray)
Console.WriteLine(str + “ “ + a);
}
}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

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private void DisplayOverload(int a, params string[] parameterArray, int b) {  }

Overload.cs

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public class Overload
    {
        public void Display()
        {
            DisplayOverload(100, 200, 300);
            DisplayOverload(200, 100);
            DisplayOverload(200);
        }

private void DisplayOverload(int a, params int[] parameterArray)
{
foreach (var i in parameterArray)
Console.WriteLine(i + “ “ + a);
}

}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

 Collapse | Copy Code

private void DisplayOverload(int a, params string[][] parameterArray)  {     }

private void DisplayOverload(int a, params string[,] parameterArray) { }

Overload.cs

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public class Overload
    {
        public void Display()
        {
            string[] names = {"Akhil", "Ekta", "Arsh"};
            DisplayOverload(3, names);
        }

private void DisplayOverload(int a, params string[] parameterArray)
{
foreach (var s in parameterArray)
Console.WriteLine(s + “ “ + a);
}

}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Overload.cs

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public class Overload
    {
        public void Display()
        {
           string [] names = {"Akhil","Arsh"};
           DisplayOverload(2, names, "Ekta");
        }

private void DisplayOverload(int a, params string[] parameterArray)
{
foreach (var str in parameterArray)
Console.WriteLine(str + “ “ + a);
}

}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

So, we got two errors. 

Overload.cs

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public class Overload
    {
        public void Display()
        {
            int[] numbers = {10, 20, 30};
            DisplayOverload(40, numbers);
            Console.WriteLine(numbers[1]);
        }

private void DisplayOverload(int a, params int[] parameterArray)
{
parameterArray[1] = 1000;
}

}

Program.cs

 Collapse | Copy Code

class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Overload.cs

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public class Overload
    {
        public void Display()
        {
            int number = 102;
            DisplayOverload(200, 1000, number, 200);
            Console.WriteLine(number);
        }

private void DisplayOverload(int a, params int[] parameterArray)
{
parameterArray[1] = 3000;
}

}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Overload.cs

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public class Overload
    {
        public void Display()
        {
            DisplayOverload(200);
            DisplayOverload(200, 300);
            DisplayOverload(200, 300, 500, 600);
        }

private void DisplayOverload(int x, int y)
{
Console.WriteLine(“The two integers “ + x + “ “ + y);
}

private void DisplayOverload(params int[] parameterArray)
{
Console.WriteLine(“parameterArray”);
}

}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            Overload overload = new Overload();
            overload.Display();
            Console.ReadKey();
        }
    }

Output

Overload.cs

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public class Overload
    {
        public static void Display(params object[] objectParamArray)
        {
            foreach (object obj in objectParamArray)
            {
                Console.Write(obj.GetType().FullName + " ");
            }
            Console.WriteLine();

}
}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            object[] objArray = { 100, "Akhil", 200.300 };
            object obj = objArray;
            Overload.Display(objArray);
            Overload.Display((object)objArray);
            Overload.Display(obj);
            Overload.Display((object[])obj);
            Console.ReadKey();

}
}

Output

Overload.cs

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public class Overload
    {
        public static void Display(params object[] objectParamArray)
        {
            Console.WriteLine(objectParamArray.GetType().FullName);
            Console.WriteLine(objectParamArray.Length);
            Console.WriteLine(objectParamArray[0]);

}
}

Program.cs

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class Program
    {
        static void Main(string[] args)
        {
            object[] objArray = { 100, "Akhil", 200.300 };
            Overload.Display((object)objArray);
            Console.ReadKey();
        }
    }

Output

5. Conclusion

1. C# recognizes the method by its parameters and not by its name.
2. The return value/parameter type of a method is never the part of method signature if the names of the methods are same. So this is not polymorphism.
3. Modifiers such as static are not considered as part of method signature.
4. The signature of a method consists of its name, number and types of its formal parameters. The return type of a function is not part of the signature. Two methods can not have the same signature and also non-members cannot have the same name as members.
5. Parameter names should be unique. And also we can not have a parameter name and a declared variable name in the same function as same.
6. In case of pass by value, the value of the variable is passed and in the case of ref and out, the address of the reference is passed.
7. This params keyword can only be applied to the last argument of the method.So the n number of parameters can only be at the end.
8. C# is very smart to recognize if the penultimate argument and the params have the same data type.
9. Parameter array must be a single dimensional array.

In upcoming articles we’ll cover topics in the same fashion.  Happy Coding.

Read more:

• C# and ASP.NET Questions (All in one)
• MVC Interview Questions
• C# and ASP.NET Interview Questions and Answers
• Web Services and Windows Services Interview Questions

Other Series

My other series of articles:

• Learning MVC
• Learning WebAPIs in .Net

For more informative articles visit my Blog.