Companion object with interfaces in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a companion object inside the class.

Kotlin

class MyClass {
    companion object [1] {
        fun greet() = "Hello"
    }
}

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

Acompanion

BcompanionObject

CCompanionObject

DCompanion

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'Companion' instead of lowercase 'companion'.

Trying to name the companion object explicitly without the keyword.

In Kotlin, the keyword companion is lowercase when declaring a companion object.

2fill in blank

medium

Complete the code to make the companion object implement the interface.

Kotlin

interface Greeter {
    fun greet(): String
}

class MyClass {
    companion object : [1] {
        override fun greet() = "Hi"
    }
}

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AGreeting

BGreeter

CGreetable

DGreets

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong interface name that does not exist.

Forgetting to add the colon before the interface name.

The companion object implements the interface named Greeter.

3fill in blank

hard

Fix the error in the companion object declaration to correctly implement the interface.

Kotlin

interface Speaker {
    fun speak(): String
}

class Talk {
    companion object [1] Speaker {
        override fun speak() = "Hello"
    }
}

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Aextends

Bimplements

C:

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'implements' like in Java.

Using 'extends' which is for class inheritance.

In Kotlin, to implement an interface, use a colon : before the interface name.

4fill in blank

hard

Fill both blanks to declare a companion object that implements two interfaces.

Kotlin

interface A {
    fun a()
}
interface B {
    fun b()
}

class Multi {
    companion object [1] [2] {
        override fun a() {}
        override fun b() {}
    }
}

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A:

B,

C;

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using semicolons or ampersands to separate interfaces.

Forgetting the colon before the interface list.

Use a colon : to start the interface list and commas , to separate multiple interfaces.

5fill in blank

hard

Fill both blanks to create a companion object that implements an interface and has a function.

Kotlin

interface Logger {
    fun log(message: String)
}

class App {
    companion object : Logger {
        fun info(msg: String) = println(msg)
        override fun log(message: String) = info([1])
    }
}

fun main() {
    App.Companion.log([2])
}

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

A:

Bmessage

C"App started"

Dmsg

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong symbols instead of colon for interface implementation.

Passing wrong variable names inside the function call.

Not using quotes around the string message.

Use colon : to implement the interface, pass the parameter message to info, and call log with the string "App started".