Primary constructor and init blocks in Kotlin - Mini Project: Build & Apply

Primary constructor and init blocks

📖 Scenario: Imagine you are creating a simple program to represent a book in a library system. Each book has a title and an author. You want to use Kotlin's primary constructor and init blocks to set up the book details and print a welcome message when a book object is created.

🎯 Goal: Build a Kotlin class called Book that uses a primary constructor to accept title and author. Use an init block to print a message confirming the book creation with its title and author.

📋 What You'll Learn

Create a class named Book with a primary constructor that takes title and author as parameters.

Use an init block inside the class to print a message: "Book created: [title] by [author]".

Create an instance of Book with the title "1984" and author "George Orwell".

Print the message from the init block automatically when the object is created.

💡 Why This Matters

🌍 Real World

Classes with primary constructors and init blocks are used to create objects with initial setup in many Kotlin applications like Android apps or backend services.

💼 Career

Understanding primary constructors and init blocks is essential for Kotlin developers to write clean and efficient code that initializes objects properly.

1

Create the Book class with primary constructor

Create a Kotlin class called Book with a primary constructor that takes two parameters: title of type String and author of type String.

Kotlin

class Book(val title: String, val author: String) {
    // Your code here
}

Need a hint?

Use the syntax: class ClassName(val param1: Type, val param2: Type) { }

2

Add an init block to print a message

Inside the Book class, add an init block that prints the message: "Book created: [title] by [author]" using the constructor parameters.

Kotlin

class Book(val title: String, val author: String) {
    init {
        // Your code here
    }
}

Need a hint?

Use an init block and println with string interpolation to show the message.

3

Create an instance of Book

Create a variable called myBook and assign it a new Book object with the title "1984" and author "George Orwell".

Kotlin

class Book(val title: String, val author: String) {
    init {
        println("Book created: $title by $author")
    }
}

// Your code here

Need a hint?

Use val myBook = Book("1984", "George Orwell") to create the object.

4

Run the program to see the output

Run the program and observe the output printed by the init block when myBook is created.

Kotlin

class Book(val title: String, val author: String) {
    init {
        println("Book created: $title by $author")
    }
}

val myBook = Book("1984", "George Orwell")

// Run the program to see the output

Need a hint?

The message should print automatically when the object is created.