Delegation vs inheritance decision in Kotlin - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to inherit from the base class.

Kotlin

open class Base {
    fun greet() = println("Hello from Base")
}

class Derived : [1]() {
}

fun main() {
    val obj = Derived()
    obj.greet()
}

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

ABase

BDerived

CAny

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using the derived class name after the colon instead of the base class.

Forgetting the parentheses after the base class name.

In Kotlin, to inherit from a class, use a colon followed by the base class name. Here, Derived inherits from Base.

2fill in blank

medium

Complete the code to delegate the interface implementation.

Kotlin

interface Printer {
    fun print()
}

class RealPrinter : Printer {
    override fun print() = println("Printing from RealPrinter")
}

class Delegator([1] printer: Printer) : Printer by printer

fun main() {
    val realPrinter = RealPrinter()
    val delegator = Delegator(realPrinter)
    delegator.print()
}

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Aopen

Bprivate

Cval

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting val or var before the parameter.

Using private which is not allowed here.

To delegate an interface in Kotlin, the constructor parameter must be a val or var so it can be used for delegation.

3fill in blank

hard

Fix the error in the delegation syntax.

Kotlin

interface Speaker {
    fun speak()
}

class Person : Speaker {
    override fun speak() = println("Person speaking")
}

class Robot([1] speaker: Speaker) : Speaker by speaker

fun main() {
    val person = Person()
    val robot = Robot(person)
    robot.speak()
}

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Avar

Bval

Cprivate

Dopen

Attempts:

3 left

💡 Hint

Common Mistakes

Using private which is not allowed for delegation parameters.

Omitting val or var.

The delegation parameter must be a property, so it needs val or var. Here, val is correct.

4fill in blank

hard

Fill both blanks to create a delegated class that overrides a method.

Kotlin

interface Logger {
    fun log(message: String)
}

class ConsoleLogger : Logger {
    override fun log(message: String) = println("Console: $message")
}

class CustomLogger([1] logger: Logger) : Logger by logger {
    override fun log(message: String) {
        println("Custom log start")
        logger.[2](message)
        println("Custom log end")
    }
}

fun main() {
    val consoleLogger = ConsoleLogger()
    val customLogger = CustomLogger(consoleLogger)
    customLogger.log("Hello")
}

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Aval

Bvar

Clog

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using var instead of val (both work but val is preferred).

Calling print instead of log.

The constructor parameter must be a property, so use val. To call the delegated method, use log.

5fill in blank

hard

Fill both blanks to create a delegated class that adds behavior before and after delegation.

Kotlin

interface Notifier {
    fun notify(message: String)
}

class EmailNotifier : Notifier {
    override fun notify(message: String) = println("Email: $message")
}

class AdvancedNotifier([1] notifier: Notifier) : Notifier by notifier {
    override fun notify(message: String) {
        println("Start notification")
        notifier.[2](message)
        println("End notification")
    }

    fun extra() = println("Extra functionality")
}

fun main() {
    val emailNotifier = EmailNotifier()
    val advNotifier = AdvancedNotifier(emailNotifier)
    advNotifier.notify("Meeting at 10")
}

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

Aval

Bnotify

Cprint

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Using print instead of notify.

Omitting val before the constructor parameter.

The constructor parameter must be a property, so use val. To call the delegated method, use notify.