How to Extend a Class in C#

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Muhammad Zeeshan Feb 02, 2024
Csharp Csharp Class
How to Extend a Class in C#

This tutorial will teach you how to extend a class using the C# programming language.

Use Inheritance to Extend a Class in C#

When working with Object-Oriented Programming (OOP), inheritance is associated with a hierarchical level. Although it is feasible to cast a derived class to its base class, we cannot do the reverse.

It is impossible to cast from a base class to a derived class. Take a look at the following example to understand better.

In the following example, we’ll add properties to the new object one at a time and then use the new object to extend a single property from the previous one.

  • To begin, import the following libraries.
    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
  • Create a Person class having Firstname and Lastname properties.
    public class Person {
  public string Firstname { get; set; }
  public string Lastname { get; set; }

  public Person(string fname, string lname) {
    Firstname = fname;
    Lastname = lname;
  }
}
  • Constructor overloading will now be used to build a Student from a Person.
    public class Student : Person {
  public Student(Person person, string code) : base(person.Firstname, person.Lastname) {
    this.code = code;
  }
  public Student(Person person) : base(person.Firstname, person.Lastname) {}
  public string code { get; set; }
}
  • In the Main() method, we’ll create a Person object and populate it with data as below.
    Person person = new Person("Muhammad Zeeshan", "Khan");
  • Then, create two Student objects named s1 and s2 and pass the person object and code as parameters.
    Student s1 = new Student(person, "3229");
Student s2 = new Student(person, "3227");
  • Lastly, we’ll print the Student objects holding Person properties.
    Console.WriteLine(s1.code);
Console.WriteLine(s2.code);
  • Complete Source Code.
    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

public class Person {
  public string Firstname { get; set; }
  public string Lastname { get; set; }

  public Person(string fname, string lname) {
    Firstname = fname;
    Lastname = lname;
  }
}

public class Student : Person {
  public Student(Person person, string code) : base(person.Firstname, person.Lastname) {
    this.code = code;
  }
  public Student(Person person) : base(person.Firstname, person.Lastname) {}
  public string code { get; set; }
}

static class Program {
  static void Main(string[] args) {
    Person person = new Person("Muhammad Zeeshan", "Khan");
    Student s1 = new Student(person, "3229");
    Student s2 = new Student(person, "3227");
    Console.WriteLine(s1.code);
    Console.WriteLine(s2.code);
  }
}

    Output:

    3229
3227
Author: Muhammad Zeeshan
Muhammad Zeeshan avatar Muhammad Zeeshan avatar

I have been working as a Flutter app developer for a year now. Firebase and SQLite have been crucial in the development of my android apps. I have experience with C#, Windows Form Based C#, C, Java, PHP on WampServer, and HTML/CSS on MYSQL, and I have authored articles on their theory and issue solving. I'm a senior in an undergraduate program for a bachelor's degree in Information Technology.

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