Project design
- Kotlin course
- Intermediate
- Lesson 112/116
- 6 min
Design the skeleton of the intermediate final mini app.
Project: Library app
In this five-lesson project you will build a library console app. Each lesson adds one piece, and by the final lesson you will have an app that combines OOP + collections + Flow + file I/O.
You will use what you learned in previous groups: data class for data modeling, sealed class for hierarchy, MutableList for collection management, java.io.File for file I/O and Flow for async streams. In the first lesson you will define the Book data class and its format method.
The Book data class
To represent a book in a library you will define data class Book. A data class generates equals, hashCode, toString and copy. The book will have a title, an author and a publication year.
data class Book(
val title: String,
val author: String,
val year: Int
) {
fun format(): String = "$title - $author ($year)"
}The format method returns a readable string: Crime and Punishment - Dostoyevsky (1866). This will be used when printing the book to the screen and saving it to a file. Later lessons will add a category property and extend format.
Practice Define the Book data class
Define data class Book(val title: String, val author: String, val year: Int). Inside it add fun format(): String = "$title - $author ($year)". In main create val b = Book("Crime and Punishment", "Dostoyevsky", 1866) and print with println(b.format()).
Starter code
// Define a Book data class: title (String), author (String), year (Int)
// format method: returns "{title} - {author} ({year})"
// main: create a Book instance and print format output with println
fun main() {
// write here
}Sample solution
data class Book(val title: String, val author: String, val year: Int) {
fun format(): String = "$title - $author ($year)"
}
fun main() {
val b = Book("Crime and Punishment", "Dostoyevsky", 1866)
println(b.format())
}Expected output
Crime and Punishment - Dostoyevsky (1866)
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is defined in the first lesson of the library project?
- A Flow stream
- The Library class
- The Book data class Correct answer
- File saving
Explanation: The first lesson defines the Book data class and its format method.
2 The data class keyword
____ class Book(val title: String, val author: String, val year: Int)data class Book(val title: String, val author: String, val year: Int)Explanation: data class Book declares a data class.
3 Match the Book parts
| Term | Meaning |
|---|---|
data class Book |
Data class |
val title |
Title |
val year |
Publication year |
format() |
Readable output |