Explicit interface implementation in C Sharp (C#) - Mini Project: Build & Apply

Explicit Interface Implementation in C#

📖 Scenario: Imagine you are building a simple system where a device can perform different actions depending on the interface it implements. Sometimes the device needs to show different behavior for the same method name depending on the interface used.

🎯 Goal: You will create two interfaces with the same method name, then implement them explicitly in a class. Finally, you will call these methods through interface references to see the different outputs.

📋 What You'll Learn

Create two interfaces named IPrinter and IScanner each with a method void Start().

Create a class named MultiFunctionDevice that implements both interfaces explicitly.

Implement Start() method for IPrinter to print "Printer starting...".

Implement Start() method for IScanner to print "Scanner starting...".

Create instances of MultiFunctionDevice and call Start() through IPrinter and IScanner references.

Print the outputs exactly as specified.

💡 Why This Matters

🌍 Real World

Explicit interface implementation is useful when a device or component supports multiple protocols or behaviors that share method names but need different implementations.

💼 Career

Understanding explicit interface implementation is important for designing clean, maintainable code in large C# projects, especially when working with APIs or frameworks that require multiple interface implementations.

1

Create interfaces IPrinter and IScanner

Create two interfaces named IPrinter and IScanner. Each interface should have a method declaration void Start().

C Sharp (C#)

// Define interface IPrinter with void Start() method
// Define interface IScanner with void Start() method

Hint

Use the interface keyword to define interfaces. Each interface should declare a method void Start(); without a body.

2

Create class MultiFunctionDevice implementing both interfaces

Create a class named MultiFunctionDevice that implements both IPrinter and IScanner interfaces explicitly. Implement Start() for IPrinter to print "Printer starting..." and for IScanner to print "Scanner starting...".

C Sharp (C#)

class MultiFunctionDevice : IPrinter, IScanner
{
    // Implement IPrinter.Start() explicitly
    // Implement IScanner.Start() explicitly
}

Hint

Use explicit interface implementation syntax: void IPrinter.Start() and void IScanner.Start() inside the class.

3

Create instances and call Start() via interface references

Create an instance of MultiFunctionDevice named device. Create two variables: printer of type IPrinter and scanner of type IScanner, both referencing device. Call Start() on printer and scanner.

C Sharp (C#)

MultiFunctionDevice device = new MultiFunctionDevice();
// Create IPrinter variable printer referencing device
// Create IScanner variable scanner referencing device
// Call Start() on printer
// Call Start() on scanner

Hint

Assign the device instance to interface variables and call Start() on each to see different outputs.

4

Print the outputs from explicit interface calls

Run the program and print the outputs from calling Start() on printer and scanner. The output should be exactly:
Printer starting...
Scanner starting...

C Sharp (C#)

// The output will be printed automatically when running the code

Hint

Run the program to see the two lines printed exactly as shown.

Practice

1. What is the main purpose of explicit interface implementation in C#?

easy

A. To separate methods with the same name from different interfaces

B. To make interface methods public by default

C. To allow interface methods to be called without casting

D. To override base class methods automatically

Solution

1. Step 1: Understand interface method conflicts

   When a class implements multiple interfaces with methods of the same name, explicit implementation helps separate them.

2. Step 2: Recognize explicit implementation behavior

   Explicit interface methods are only accessible through the interface, avoiding confusion and conflicts.

3. Final Answer:

   To separate methods with the same name from different interfaces -> Option A

4. Quick Check:

   Explicit interface implementation = separate same-named methods [OK]

Hint: Explicit means access only via interface, not class object [OK]

Common Mistakes:

• Thinking explicit makes methods public on the class
• Assuming explicit allows calling without casting
• Confusing explicit with overriding base methods

2. Which of the following is the correct syntax for explicit interface implementation of method Show() from interface IExample in class Demo?

easy

A. public void Show() { }

B. public void IExample.Show() { }

C. void IExample.Show() { }

D. void Show() IExample { }

Solution

1. Step 1: Recall explicit implementation syntax

   Explicit interface methods are implemented with the interface name before the method: void InterfaceName.MethodName().

2. Step 2: Match correct syntax

   void IExample.Show() { } matches this pattern exactly: void IExample.Show() { }.

3. Final Answer:

   void IExample.Show() { } -> Option C

4. Quick Check:

   Explicit syntax = void Interface.Method() [OK]

Hint: Explicit methods use interface name before method [OK]

Common Mistakes:

• Adding public modifier to explicit method
• Placing interface name after method name
• Using invalid syntax like 'void Show() IExample'

3. What will be the output of the following code?

interface IA { void Display(); }
interface IB { void Display(); }
class Test : IA, IB {
    void IA.Display() { Console.WriteLine("IA Display"); }
    void IB.Display() { Console.WriteLine("IB Display"); }
}

var obj = new Test();
// obj.Display(); // Line A
((IA)obj).Display();
((IB)obj).Display();

medium

A. Compilation error at Line A

B. IA Display\nIB Display

C. IB Display\nIA Display

D. Runtime error

Solution

1. Step 1: Understand explicit interface calls

   Explicit interface methods cannot be called directly on the class object, so obj.Display() causes error if uncommented.

2. Step 2: Check interface casts and calls

   Casting to IA calls IA.Display() printing "IA Display"; casting to IB calls IB.Display() printing "IB Display".

3. Final Answer:

   IA Display IB Display -> Option B

4. Quick Check:

   Explicit calls via interface = correct output [OK]

Hint: Call explicit methods only via interface cast [OK]

Common Mistakes:

• Trying to call explicit method directly on class object
• Mixing output order
• Expecting runtime errors instead of compile errors

4. Identify the error in the following code snippet implementing explicit interface method:

interface IAlpha { void Run(); }
class Beta : IAlpha {
    public void IAlpha.Run() {
        Console.WriteLine("Running");
    }
}

medium

A. Explicit interface method cannot have public modifier

B. Method name must be different from interface

C. Interface name should not be used in method implementation

D. Missing override keyword

Solution

1. Step 1: Check explicit implementation rules

   Explicit interface methods must not have access modifiers like public; they are implicitly private.

2. Step 2: Identify error in code

   The code uses public void IAlpha.Run(), which is invalid syntax for explicit implementation.

3. Final Answer:

   Explicit interface method cannot have public modifier -> Option A

4. Quick Check:

   Explicit methods = no public keyword [OK]

Hint: Remove public from explicit interface methods [OK]

Common Mistakes:

• Adding public modifier to explicit methods
• Confusing explicit with normal method override
• Forgetting interface name in method signature

5. Given two interfaces IX and IY both having method Process(), how can a class Worker implement both explicitly and allow calling Process() without casting?

hard

A. Use inheritance instead of interfaces

B. Implement explicit methods only, no public method needed

C. Implement only one interface explicitly and the other implicitly

D. Implement explicit methods and add a public method calling one interface method

Solution

1. Step 1: Understand explicit implementation limits

   Explicit interface methods are accessible only via interface references, not directly on class objects.

2. Step 2: Provide public method to call explicit method

   To call Process() without casting, class must have a public method that internally calls one explicit interface method.

3. Final Answer:

   Implement explicit methods and add a public method calling one interface method -> Option D

4. Quick Check:

   Public wrapper calls explicit method = direct access [OK]

Hint: Add public method calling explicit interface method [OK]

Common Mistakes:

• Expecting explicit methods callable without casting
• Implementing only one interface explicitly
• Ignoring need for public wrapper method