Explicit interface implementation in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to explicitly implement the interface method.

C Sharp (C#)

interface IExample {
    void Show();
}

class Demo : IExample {
    void IExample.[1]() {
        Console.WriteLine("Explicit implementation");
    }
}

Drag options to blanks, or click blank then click option'

AShow

BDisplay

CShowMessage

DPrint

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name than the interface method.

Forgetting to prefix the method with the interface name.

The method name must match the interface method exactly for explicit implementation.

2fill in blank

medium

Complete the code to call the explicitly implemented interface method from an interface reference.

C Sharp (C#)

interface IExample {
    void Show();
}

class Demo : IExample {
    void IExample.Show() {
        Console.WriteLine("Explicit implementation");
    }
}

class Program {
    static void Main() {
        Demo obj = new Demo();
        IExample iobj = obj;
        iobj.[1]();
    }
}

Drag options to blanks, or click blank then click option'

AShow

BDisplay

CPrint

DShowMessage

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the method directly from the class instance.

Using a wrong method name.

You must call the interface method name through the interface reference.

3fill in blank

hard

Fix the error in the explicit interface implementation method signature.

C Sharp (C#)

interface IExample {
    void Show();
}

class Demo : IExample {
    void IExample.[1]() {
        Console.WriteLine("Explicit implementation");
    }
}

Drag options to blanks, or click blank then click option'

AShowMessage

BDisplay

CPrint

DShow

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 'public' or other access modifiers to explicit interface methods.

Using a different method name than the interface.

Explicit interface implementations cannot have access modifiers like 'public'.

4fill in blank

hard

Fill both blanks to explicitly implement two interface methods correctly.

C Sharp (C#)

interface IFirst {
    void MethodA();
}
interface ISecond {
    void MethodB();
}

class Demo : IFirst, ISecond {
    void IFirst.[1]() {
        Console.WriteLine("First method");
    }
    void ISecond.[2]() {
        Console.WriteLine("Second method");
    }
}

Drag options to blanks, or click blank then click option'

AMethodA

BMethodC

CMethodB

DMethodD

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up method names between interfaces.

Using incorrect method names.

Each method must match its interface method name exactly for explicit implementation.

5fill in blank

hard

Fill all three blanks to explicitly implement an interface and call its method correctly.

C Sharp (C#)

interface IExample {
    void Show();
}

class Demo : IExample {
    void IExample.[1]() {
        Console.WriteLine("Explicit implementation");
    }
}

class Program {
    static void Main() {
        Demo obj = new Demo();
        IExample iobj = [2];
        iobj.[3]();
    }
}

Drag options to blanks, or click blank then click option'

AShow

Bobj

Ddemo

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names for the interface reference.

Calling the method directly from the class instance instead of the interface reference.

The method name must match the interface method, the interface reference must be assigned correctly, and the method called must be the interface method.

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