Sealed classes with when exhaustive check in Kotlin - Mini Project: Build & Apply

Sealed classes with when exhaustive check

📖 Scenario: Imagine you are building a simple app that handles different types of notifications: Email, SMS, and Push notifications. Each notification type has its own data.

🎯 Goal: You will create sealed classes to represent these notification types and use a when expression to handle each type with an exhaustive check.

📋 What You'll Learn

Create a sealed class called Notification with three subclasses: Email, SMS, and Push

Add properties to each subclass as specified

Create a variable called notification with a specific subclass instance

Use a when expression with exhaustive check to handle all notification types

Print a message describing the notification

💡 Why This Matters

🌍 Real World

Sealed classes help represent fixed sets of related types, like different notification types in an app, making code safer and easier to maintain.

💼 Career

Understanding sealed classes and exhaustive <code>when</code> expressions is important for Kotlin developers building robust and clear applications.

1

Create sealed class and subclasses

Create a sealed class called Notification with three subclasses: Email with a subject property of type String, SMS with a phoneNumber property of type String, and Push with a message property of type String.

Kotlin

# Create sealed class Notification and subclasses Email, SMS, Push
// Your code here

Need a hint?

Use sealed class Notification and inside it define data class Email, SMS, and Push each inheriting from Notification.

2

Create a notification instance

Create a variable called notification and assign it an instance of Notification.Email with the subject set to "Welcome to Kotlin".

Kotlin

sealed class Notification {
    data class Email(val subject: String) : Notification()
    data class SMS(val phoneNumber: String) : Notification()
    data class Push(val message: String) : Notification()
}

// Create variable notification as Email with subject "Welcome to Kotlin"
// Your code here

Need a hint?

Use val notification: Notification = Notification.Email("Welcome to Kotlin") to create the instance.

3

Use when expression with exhaustive check

Write a when expression using the variable notification to handle all subclasses: Email, SMS, and Push. For each case, create a string message describing the notification. Assign the result to a variable called message. Make sure the when expression is exhaustive.

Kotlin

sealed class Notification {
    data class Email(val subject: String) : Notification()
    data class SMS(val phoneNumber: String) : Notification()
    data class Push(val message: String) : Notification()
}

val notification: Notification = Notification.Email("Welcome to Kotlin")

// Use when expression with exhaustive check to assign message
// Your code here

Need a hint?

Use val message = when (notification) { ... } with all subclasses handled.

4

Print the message

Write a println statement to display the value of the variable message.

Kotlin

sealed class Notification {
    data class Email(val subject: String) : Notification()
    data class SMS(val phoneNumber: String) : Notification()
    data class Push(val message: String) : Notification()
}

val notification: Notification = Notification.Email("Welcome to Kotlin")

val message = when (notification) {
    is Notification.Email -> "Email with subject: ${notification.subject}"
    is Notification.SMS -> "SMS to phone number: ${notification.phoneNumber}"
    is Notification.Push -> "Push notification: ${notification.message}"
}

// Print the message
println()

Need a hint?

Use println(message) to display the message.