Inheritance

1. Description

Inheritance is a fundamental principle of Object-Oriented Programming (OOP) that allows a class to inherit properties and methods from another class. The class that is being inherited from is called the base class (or superclass), and the class that inherits is called the derived class (or subclass).

The derived class can reuse the code from the base class, extend it with new functionality, and modify its behavior (through method overriding).

2. Why It Is Important

Inheritance is a powerful mechanism for code reuse and for establishing relationships between classes. It allows you to:

• Avoid Code Duplication: Common functionality can be placed in a base class and reused across multiple derived classes.
• Create a Logical Hierarchy: You can model "is-a" relationships (e.g., a Dog is an Animal, a Student is a Person).
• Enable Polymorphism: Inheritance is a prerequisite for polymorphism, which allows you to treat objects of different derived classes as objects of the base class.

3. Real-World Examples

• A Vehicle base class can have properties like Speed and Color. Derived classes like Car, Truck, and Motorcycle can inherit these properties and add their own specific ones (e.g., NumberOfDoors for a Car).
• In a UI framework, you might have a base Control class with properties like Position and Size, and derived classes like Button, TextBox, and Checkbox.
• A Person class can be a base class for Student, Teacher, and Administrator classes in a university management system.

4. Syntax & Explanation

using System;

// Base class
public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public string FullName => $"{FirstName} {LastName}";

    public void Greet()
    {
        Console.WriteLine($"Hello, my name is {FullName}.");
    }
}

// Derived class 'Student' inherits from 'Person'
public class Student : Person
{
    public string StudentNumber { get; set; }
    public string Major { get; set; }
}

// Derived class 'Teacher' also inherits from 'Person'
public class Teacher : Person
{
    public string EmployeeNumber { get; set; }
    public string Department { get; set; }
}

class Program
{
    static void Main()
    {
        // Create a Student object
        var student = new Student
        {
            FirstName = "Alice",
            LastName = "Smith",
            Major = "Computer Science"
        };

        // Create a Teacher object
        var teacher = new Teacher
        {
            FirstName = "Bob",
            LastName = "Johnson",
            Department = "Physics"
        };
        
        // Both 'student' and 'teacher' have access to the properties and methods of the 'Person' class.
        Console.WriteLine(student.FullName); // Inherited from Person
        student.Greet();                     // Inherited from Person

        Console.WriteLine(teacher.FullName); // Inherited from Person
        teacher.Greet();                     // Inherited from Person
    }
}

5. Use Cases

• Sharing common code: When you have multiple classes that share the same set of properties or methods.
• Creating specialized versions of a class: A derived class is often a more specialized version of the base class.
• Framework development: Base classes in frameworks often provide core functionality that developers can extend to fit their specific needs.

6. Mini Practice Task

1. Create a base class called Animal with a Name property and a method Eat() that prints a generic message like "{Name} is eating."
2. Create two derived classes, Dog and Cat, that inherit from Animal.
3. Add a Bark() method to the Dog class and a Meow() method to the Cat class.
4. In your Main method, create instances of Dog and Cat, set their names, and call both their specific methods (Bark/Meow) and the inherited method (Eat).