Inheritance in C#

Inheritance is a fundamental concept in OOPs that allows a class to inherit properties and behaviors of another class. We have two key terms are here base class/superclass and derived class/subclass.

• Base class / super-class: Whose members and functionality are inherited (Giver).
• Derived class / sub-class: Who is inheriting the members (Taker)

📺Other oops concepts:

• Abstraction in C#
• Encapsulation in C#
• Polymorphism in C#

Syntax of inheritance:

class BaseClass
{
  // content
}

class DerivedClass: BaseClass
{
 // content
}

Let’s understand it with example.

👉Base class: Phone

public class Phone
{
    public string Brand { get; set; }
    public string Model { get; set; }
    public int Year { get; set; }

    public void Call()
    {
        Console.WriteLine("Making a phone call.");
    }

    public void Text()
    {
        Console.WriteLine("Sending a text message.");
    }

    public virtual void DisplayInfo()
    {
        Console.WriteLine($"Brand: {Brand}");
        Console.WriteLine($"Model: {Model}");
        Console.WriteLine($"Year: {Year}");
    }
}

👉Derived class: Smart phone

public class Smartphone : Phone
{
    public string OperatingSystem { get; set; }

    public override void DisplayInfo()
    {
        base.DisplayInfo();
        Console.WriteLine($"Operating System: {OperatingSystem}");
    }

    public void BrowseInternet()
    {
        Console.WriteLine("Browsing the internet on the smartphone.");
    }
}

👉Derived class: Basic phone

public class BasicPhone : Phone
{
    public bool HasPhysicalKeypad { get; set; }

    public override void DisplayInfo()
    {
        base.DisplayInfo();
        Console.WriteLine($"Has Physical Keypad: {HasPhysicalKeypad}");
    }

    public void MakeSimpleCall()
    {
        Console.WriteLine("Making a call on the basic phone.");
    }
}

Calling it in main method:

Smartphone mySmartphone = new Smartphone
{
    Brand = "Samsung",
    Model = "Galaxy S21",
    Year = 2022,
    OperatingSystem = "Android"
};

BasicPhone myBasicPhone = new BasicPhone
{
    Brand = "Nokia",
    Model = "3310",
    Year = 2000,
    HasPhysicalKeypad = true
};

// Display phone information
Console.WriteLine("Smartphone Information:");
mySmartphone.DisplayInfo();
mySmartphone.Call();
mySmartphone.BrowseInternet();

Console.WriteLine("\nBasic Phone Information:");
myBasicPhone.DisplayInfo();
myBasicPhone.Call();
myBasicPhone.MakeSimpleCall();

😎Let’s Break it down:

• Every phone have some common features like (Brand, Model, Year, Call, Text). If we have two classes BasicPhone and SmartPhone, we need to write these features in both classes, which leads to unnecessary code redundancy. It is beneficial to create one Base-Class (Phone) and put all the common functionality there(in Phone class). Both classes (BasicPhone and SmartPhone) will re-use the common f functionality by inheritance. Now BasicPhone and SmartPhone will not have any redundant code.
• Phone is a base class. BasicPhone and SmartPhone are derived classes.
• Extending Functionality: The subclass can extend or override the functionality of the superclass. It can add new methods or properties, or override existing ones to suit its specific needs. In the above example , derived classes are overriding the DisplayInfo() method.

Commonly known inheritance:

• Single inheritance: Previous example was single inheritance . BasicPhone class inherit the Phone class.
• Multilevel inheritance: Animal is inherited by Mammal and Mammal is inherited by Dog

// Base class
class Animal {
    public void Eat() {
        Console.WriteLine("Animal is eating.");
    }
}

// First derived class
class Mammal : Animal {
    public void GiveBirth() {
        Console.WriteLine("Mammal gives birth.");
    }
}

// Second derived class (inherits from Mammal)
class Dog : Mammal {
    public void Bark() {
        Console.WriteLine("Dog is barking.");
    }
}

class Program
{
    static void Main()
    {
        Dog myDog = new Dog();
        myDog.Eat();         // Inherited from Animal
        myDog.GiveBirth();   // Inherited from Mammal
        myDog.Bark();        // Method from Dog class
    }
}

• Multiple inheritance:

Eg. Class C inherits Class A and Class B (C:A,B)

⚠️Multiple inheritance is not allowed in c#. Why? Because of diamond problem.

✏️Diamond Problem: Multiple inheritance can lead to a situation known as the “diamond problem.” This occurs when a class inherits from two classes that have a common ancestor. If there are conflicting methods or members in the common ancestor, it becomes ambiguous for the derived class to determine which implementation to use. This can result in confusion and errors.

// Diamond problem example (not allowed in C#)
class A { public void DoSomething() { /* ... */ } }
class B : A { public void DoSomethingElse() { /* ... */ } }
class C : A { public void DoYetAnotherThing() { /* ... */ } }
class D : B, C { } // Ambiguity arises here

Class B inherits class A, which have DoSomething() method. Class C also inherits class A. If D inherits B and C, it will get two DoSomething() methods which is ambiguous. That’s why multiple inheritance is not allowed in c#.

👏Solution for multiple inheritance (Interface-based Approach): C# provides a way to achieve some benefits of multiple inheritance through interfaces. Classes can implement multiple interfaces, allowing them to inherit method signatures from multiple sources without the ambiguity associated with multiple inheritance. Since interface does not contain any method definition, that’s why can’t be any ambiguity.

interface IDrawable { void Draw(); }
interface IResizable { void Resize(); }

class Shape : IDrawable, IResizable {
    public void Draw() { /* ... */ }
    public void Resize() { /* ... */ }
}

That’s is all about inheritance.

Polymorphism in c#

Encapsulation in C#

Abstraction in C#

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