Implementing interfaces in C Sharp (C#) - Mini Project: Build & Apply

Implementing interfaces

📖 Scenario: You are creating a simple program to manage different types of vehicles. Each vehicle can start and stop, but the way they do it might differ. To keep things organized, you will use an interface to define these actions.

🎯 Goal: Build a C# program that defines an interface IVehicle with methods Start() and Stop(). Then create two classes Car and Bike that implement this interface. Finally, create objects of these classes and call their methods.

📋 What You'll Learn

Create an interface called IVehicle with methods Start() and Stop().

Create a class called Car that implements IVehicle.

Create a class called Bike that implements IVehicle.

In each class, implement Start() and Stop() methods with simple Console.WriteLine messages.

Create objects of Car and Bike and call their Start() and Stop() methods.

💡 Why This Matters

🌍 Real World

Interfaces are used in software to define common behaviors that different classes must implement, like how different vehicles share start and stop actions.

💼 Career

Understanding interfaces is essential for writing clean, maintainable code in many programming jobs, especially in object-oriented programming.

1

Create the interface IVehicle

Create an interface called IVehicle with two methods: void Start() and void Stop().

C Sharp (C#)

// Your code here
// Define interface IVehicle with Start() and Stop() methods

Hint

An interface in C# uses the interface keyword and only declares method signatures without bodies.

2

Create the Car class implementing IVehicle

Create a class called Car that implements the IVehicle interface. Implement the Start() method to print "Car started" and the Stop() method to print "Car stopped" using Console.WriteLine.

C Sharp (C#)

public interface IVehicle
{
    void Start();
    void Stop();
}

// Your code here
// Define class Car implementing IVehicle with Start() and Stop() methods

Hint

Use public class Car : IVehicle to implement the interface. Implement both methods with Console.WriteLine messages.

3

Create the Bike class implementing IVehicle

Create a class called Bike that implements the IVehicle interface. Implement the Start() method to print "Bike started" and the Stop() method to print "Bike stopped" using Console.WriteLine.

C Sharp (C#)

public interface IVehicle
{
    void Start();
    void Stop();
}

public class Car : IVehicle
{
    public void Start()
    {
        Console.WriteLine("Car started");
    }

    public void Stop()
    {
        Console.WriteLine("Car stopped");
    }
}

// Your code here
// Define class Bike implementing IVehicle with Start() and Stop() methods

Hint

Similar to Car, implement Bike with the interface methods printing the correct messages.

4

Create objects and call methods

In the Main method, create an object of Car called myCar and an object of Bike called myBike. Call Start() and Stop() on both objects. Use Console.WriteLine to display the messages from these methods.

C Sharp (C#)

public interface IVehicle
{
    void Start();
    void Stop();
}

public class Car : IVehicle
{
    public void Start()
    {
        Console.WriteLine("Car started");
    }

    public void Stop()
    {
        Console.WriteLine("Car stopped");
    }
}

public class Bike : IVehicle
{
    public void Start()
    {
        Console.WriteLine("Bike started");
    }

    public void Stop()
    {
        Console.WriteLine("Bike stopped");
    }
}

class Program
{
    static void Main()
    {
        // Your code here
        // Create objects myCar and myBike and call Start() and Stop() on both
    }
}

Hint

Create objects using new keyword and call the methods directly. The output should show the messages in order.

Practice

1. What does it mean to implement an interface in C#?

easy

A. A class provides code for all methods declared in the interface.

B. An interface inherits from a class.

C. A class hides all methods of the interface.

D. An interface creates objects directly.

Solution

1. Step 1: Understand interface purpose

   An interface declares methods without code, setting a contract.

2. Step 2: Implementing means coding methods

   A class that implements the interface must write the code for all those methods.

3. Final Answer:

   A class provides code for all methods declared in the interface. -> Option A

4. Quick Check:

   Implementing interface = writing required methods [OK]

Hint: Implementing means writing all interface methods in the class [OK]

Common Mistakes:

• Thinking interfaces can create objects
• Believing interfaces inherit from classes
• Assuming methods are hidden, not implemented

2. Which of the following is the correct syntax to implement an interface IMyInterface in a class MyClass?

easy

A. interface MyClass : IMyInterface { }

B. class MyClass : IMyInterface { }

C. class MyClass implements IMyInterface { }

D. class MyClass inherits IMyInterface { }

Solution

1. Step 1: Recall C# interface syntax

   In C#, a class implements an interface using a colon (:), not 'implements' or 'inherits'.

2. Step 2: Check each option

   class MyClass : IMyInterface { } uses correct syntax: class MyClass : IMyInterface { }. Others use wrong keywords or declare interface as class.

3. Final Answer:

   class MyClass : IMyInterface { } -> Option B

4. Quick Check:

   Use colon (:) to implement interface [OK]

Hint: Use ':' to implement interface, not 'implements' or 'inherits' [OK]

Common Mistakes:

• Using 'implements' keyword like Java
• Trying to inherit interface with 'inherits'
• Declaring interface as a class

3. What will be the output of this code?

interface IGreet { void SayHello(); }
class Person : IGreet {
  public void SayHello() { Console.WriteLine("Hi!"); }
}
var p = new Person();
p.SayHello();

medium

A. No output

B. SayHello

C. Hi!

D. Compile error

Solution

1. Step 1: Understand interface and class

   The interface IGreet requires SayHello method. Person implements it by printing "Hi!".

2. Step 2: Trace code execution

   Creating Person object and calling SayHello prints "Hi!" to console.

3. Final Answer:

   Hi! -> Option C

4. Quick Check:

   Implemented method runs and prints output [OK]

Hint: Implemented method runs exactly as coded in class [OK]

Common Mistakes:

• Expecting method name printed instead of output
• Thinking interface prints output
• Assuming compile error without method body

4. Identify the error in this code:

interface IRun { void Run(); }
class Animal : IRun { }

medium

A. Class Animal must implement Run method.

B. Interface IRun cannot be empty.

C. Class Animal cannot implement interface.

D. No error, code is correct.

Solution

1. Step 1: Check interface requirements

   IRun interface requires a method Run() to be implemented.

2. Step 2: Verify class implementation

   Animal class implements IRun but does not provide Run() method, causing error.

3. Final Answer:

   Class Animal must implement Run method. -> Option A

4. Quick Check:

   Implement all interface methods [OK]

Hint: All interface methods must be in the class [OK]

Common Mistakes:

• Forgetting to implement interface methods
• Thinking interfaces must have code
• Assuming empty class is allowed

5. You have two interfaces:

interface IWalk { void Walk(); }
interface ITalk { void Talk(); }

How can a class Human implement both interfaces correctly?

hard

A. interface Human : IWalk, ITalk { }

B. class Human : IWalk { public void Walk() { } } class Human : ITalk { public void Talk() { } }

C. class Human implements IWalk, ITalk { }

D. class Human : IWalk, ITalk { public void Walk() { Console.WriteLine("Walking"); } public void Talk() { Console.WriteLine("Talking"); } }

Solution

1. Step 1: Understand multiple interface implementation

   A class can implement multiple interfaces by listing them separated by commas.

2. Step 2: Provide all required methods

   Human class must provide Walk() and Talk() methods with code.

3. Final Answer:

   class Human : IWalk, ITalk { public void Walk() { Console.WriteLine("Walking"); } public void Talk() { Console.WriteLine("Talking"); } } -> Option D

4. Quick Check:

   Multiple interfaces implemented with all methods [OK]

Hint: Separate interfaces with commas and implement all methods [OK]

Common Mistakes:

• Trying to declare multiple classes with same name
• Using 'implements' keyword (Java style)
• Declaring interface instead of class