Interface with default implementations in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an interface with a default implementation for the greet function.

Kotlin

interface Greeter {
    fun greet() {
        println([1])
    }
}

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

A"Hello from interface!"

Bgreet()

Cprintln("Hello")

Dfun greet()

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call greet() inside its own body causing recursion.

Using function declaration syntax inside the function body.

The greet function in the interface has a default implementation that prints the greeting message.

2fill in blank

medium

Complete the code to implement the Greeter interface and override the greet function.

Kotlin

class FriendlyGreeter : Greeter {
    override fun greet() {
        println([1])
    }
}

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

Agreet()

B"Hi there!"

Cprintln("Hello")

Dsuper.greet()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling greet() inside itself causing infinite recursion.

Trying to call super.greet() without a proper context.

The FriendlyGreeter class overrides greet to print a custom message.

3fill in blank

hard

Fix the error in the code to call the default greet implementation from the interface inside the override.

Kotlin

class PoliteGreeter : Greeter {
    override fun greet() {
        [1].greet()
        println("Have a nice day!")
    }
}

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

Athis

Bsuper

CGreeter.super

DPoliteGreeter.super

Attempts:

3 left

💡 Hint

Common Mistakes

Using just super.greet() which is invalid for interfaces.

Using this.greet() causing recursion.

To call the interface's default implementation, use InterfaceName.super.methodName() syntax.

4fill in blank

hard

Fill both blanks to define an interface with a default method and a class that calls it.

Kotlin

interface Speaker {
    fun speak() {
        println([1])
    }
}

class Person : Speaker {
    fun sayHello() {
        [2].speak()
    }
}

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

A"Hello!"

BSpeaker.super

Cthis

D"Hi!"

Attempts:

3 left

💡 Hint

Common Mistakes

Using this.speak() instead of Speaker.super.speak().

Not providing a string literal in the interface method.

The interface method prints "Hello!" and the class calls the default speak using Speaker.super.

5fill in blank

hard

Fill all three blanks to create an interface with a default method, a class overriding it, and calling both versions.

Kotlin

interface Animal {
    fun sound() {
        println([1])
    }
}

class Dog : Animal {
    override fun sound() {
        println([2])
        [3].sound()
    }
}

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

A"Generic animal sound"

B"Bark!"

CAnimal.super

D"Meow!"

Attempts:

3 left

💡 Hint

Common Mistakes

Using super.sound() instead of Animal.super.sound() for interface default call.

Not overriding the sound method properly.

The interface prints a generic sound, Dog overrides with "Bark!" and calls the default using Animal.super.sound().