Model design
- Kotlin course
- Intermediate
- Lesson 59/116
- 6 min
Design the skeleton of Book and Member data classes.
Project: Library app
In this five-lesson project you will build a library application. Each lesson adds one piece, and by the final lesson book and member management, checkout, search and command handling come together.
You will use data class from previous groups to define data classes. In the first lesson you define two models: Book with three fields and Member with two fields. Both are written as data class, so toString is generated automatically and println gives readable output.
Book and Member fields
The Book model carries three properties: title, author and isbn. All are of type String and cannot be empty.
The Member model carries two properties: name and id. Example definition: data class Member(val name: String, val id: String). When an instance is printed with println, it produces readable output like Member(name=Alex, id=M1). You will use this output for testing in later lessons.
Practice Define the Book and Member models
Define data class Book(val title: String, val author: String, val isbn: String) and data class Member(val name: String, val id: String). In main create Book("War and Peace", "Tolstoy", "978-1") and Member("Alex", "M1") instances and print each with println.
Starter code
fun main() {
// Create Book and Member instances and print with println
}
// Define the Book data class: title, author, isbn (all String)
// Define the Member data class: name, id (all String)Sample solution
data class Book(val title: String, val author: String, val isbn: String)
data class Member(val name: String, val id: String)
fun main() {
val b = Book("War and Peace", "Tolstoy", "978-1")
val m = Member("Alex", "M1")
println(b)
println(m)
}Expected output
Book(title=War and Peace, author=Tolstoy, isbn=978-1) Member(name=Alex, id=M1)
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which line correctly defines the Book model?
- data class Book(title: String, author: String, isbn: String)
- class Book(val title: String, val author: String, val isbn: String)
- data class Book(val title: String, val author: String, val isbn: String) Correct answer
- data class Book(val title, val author, val isbn)
Explanation: With the data modifier and val parameters the Book data class is defined correctly.
2 Complete the Member data class
data class Member(val name: String, val ____: String)data class Member(val name: String, val id: String)Explanation: The Member class carries name and id properties.
3 Match the model fields
| Term | Meaning |
|---|---|
Book.title |
Book title |
Book.isbn |
Book number |
Member.name |
Member name |
Member.id |
Member number |