Multiple interface implementation in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of multiple interface implementation with explicit methods

What is the output of this C# program that implements two interfaces with explicit method implementations?

C Sharp (C#)

using System;
interface IA { void Show(); }
interface IB { void Show(); }
class Demo : IA, IB {
    void IA.Show() { Console.WriteLine("IA Show"); }
    void IB.Show() { Console.WriteLine("IB Show"); }
}
class Program {
    static void Main() {
        Demo d = new Demo();
        ((IA)d).Show();
        ((IB)d).Show();
    }
}

A IA Show\nIB Show

B Compilation error due to ambiguous Show method

C Show\nShow

D IB Show\nIA Show

💡 Hint

Explicit interface implementations require casting to the interface to call the method.

The class Demo implements IA.Show and IB.Show explicitly. To call these methods, you must cast the object to the interface type. The calls ((IA)d).Show() and ((IB)d).Show() invoke the respective interface implementations, printing 'IA Show' and 'IB Show'.

❓ Predict Output

intermediate

Output when calling method without explicit interface cast

Given this code, what will be the output when calling Show() directly on the object?

C Sharp (C#)

using System;
interface IA { void Show(); }
interface IB { void Show(); }
class Demo : IA, IB {
    public void Show() { Console.WriteLine("Demo Show"); }
    void IA.Show() { Console.WriteLine("IA Show"); }
    void IB.Show() { Console.WriteLine("IB Show"); }
}
class Program {
    static void Main() {
        Demo d = new Demo();
        d.Show();
    }
}

A Compilation error due to ambiguous Show method

B IB Show

C Demo Show

D IA Show

💡 Hint

Public method Show() in the class is called directly without casting.

The class Demo has a public Show() method. This method is called directly on the object d, so it prints 'Demo Show'. The explicit interface implementations are not called unless the object is cast to the interface.

🔧 Debug

advanced

Identify the error in multiple interface implementation

What error will this code produce when compiled?

C Sharp (C#)

interface IA { void Display(); }
interface IB { void Display(); }
class Test : IA, IB {
    public void Display() { }
    public void Display(int x) { }
}

A Compilation error: 'Test' does not implement interface member 'IB.Display()'

B Compilation error: Method 'Display(int)' hides inherited member

C Runtime error: Ambiguous method call

D No compilation error, code compiles successfully

💡 Hint

Check if all interface members are implemented explicitly or implicitly.

The class Test has a public Display() method that matches IA.Display() and IB.Display(). Since both interfaces have the same method signature, the single public method satisfies both. The overload Display(int x) does not affect interface implementation. Therefore, the code compiles successfully.

📝 Syntax

advanced

Which option correctly implements two interfaces with same method name?

Select the option that correctly implements interfaces IA and IB, both having void Run(), in one class without ambiguity.

A class C : IA, IB { void IA.Run() { } void IB.Run() { } }

B class C : IA, IB { public void Run() { } }

C class C : IA, IB { public void Run() { } void IB.Run() { } }

D class C : IA, IB { void Run() { } }

💡 Hint

Explicit interface implementation avoids ambiguity when methods have same signature.

Option A uses explicit interface implementation for both IA.Run() and IB.Run(), so the class implements both interfaces without ambiguity. Option A compiles but the single Run() method implements both interfaces implicitly. Option A is invalid because IB.Run() is explicit but IA.Run() is implicit, causing ambiguity. Option A is invalid because void Run() without access modifier is private and does not implement interfaces.

🚀 Application

expert

Determine the output of interface method calls with inheritance and multiple interfaces

Consider these interfaces and classes. What is the output when running the Main method?

C Sharp (C#)

using System;
interface IA { void Action(); }
interface IB : IA { void Action(); }
class Base : IA {
    public virtual void Action() { Console.WriteLine("Base Action"); }
}
class Derived : Base, IB {
    public override void Action() { Console.WriteLine("Derived Action"); }
}
class Program {
    static void Main() {
        Derived d = new Derived();
        IA ia = d;
        IB ib = d;
        Base b = d;
        d.Action();
        ia.Action();
        ib.Action();
        b.Action();
    }
}

A Base Action\nBase Action\nBase Action\nBase Action

B Derived Action\nDerived Action\nDerived Action\nDerived Action

C Derived Action\nBase Action\nDerived Action\nBase Action

D Compilation error due to interface inheritance conflict

💡 Hint

Virtual and override methods are called based on the actual object type, not the reference type.

The Derived class overrides the virtual method Action from Base. All references (IA, IB, Base, Derived) point to the same Derived object. Calling Action() on any of these calls the overridden Derived.Action(), printing 'Derived Action' four times.