Default interface methods in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a default method in the interface.

C Sharp (C#)

public interface IExample {
    void Show();
    [1] DefaultMethod() {
        Console.WriteLine("Default implementation");
    }
}

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

Adefault

Bpublic

Cstatic

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'default' keyword before method name.

Trying to make the method static inside interface.

The method in an interface with a default implementation must have an access modifier like public. The keyword default is not used here.

2fill in blank

medium

Complete the code to call the default interface method from a class implementing the interface.

C Sharp (C#)

public class MyClass : IExample {
    public void Show() {
        Console.WriteLine("Show method");
    }
    public void CallDefault() {
        [1].DefaultMethod();
    }
}

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

AIExample

Bbase

Cthis

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this' or 'base' to call the interface method.

Trying to call the method without specifying the interface.

To call a default interface method explicitly, you use the interface name followed by the method.

3fill in blank

hard

Fix the error in the interface default method declaration.

C Sharp (C#)

public interface ICalc {
    [1] int Add(int a, int b) {
        return a + b;
    }
}

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

Apublic

Bvoid

Cstatic

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'default' keyword incorrectly.

Declaring the method as 'static' inside interface.

Interface methods with default implementations must be declared with an access modifier like public. The default keyword is not used here.

4fill in blank

hard

Fill both blanks to create a default method with a return value and call it from the class.

C Sharp (C#)

public interface IPrinter {
    [1] string GetMessage() {
        return "Hello from interface";
    }
}

public class Printer : IPrinter {
    public string GetMessage() {
        return [2].GetMessage();
    }
}

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

Apublic

BIPrinter

Cdefault

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'default' keyword in method declaration.

Using 'this' instead of interface name to call the method.

The default method must be declared public. To call it from the class, use the interface name.

5fill in blank

hard

Fill all three blanks to override a default interface method in a class and call both versions.

C Sharp (C#)

public interface ILogger {
    [1] void Log(string message) {
        Console.WriteLine($"Interface log: {message}");
    }
}

public class Logger : ILogger {
    public void Log(string message) {
        Console.WriteLine($"Class log: {message}");
        [2].[3](message);
    }
}

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

Apublic

BILogger

CLog

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'default' keyword in method declaration.

Trying to call the default method without interface name.

The interface method must be declared public. To call the default method from the class, use the interface name and method name.