Summary - Data class
- Kotlin course
- Intermediate
- Lesson 18/116
- 5 min
Combine data class, copy and destructuring to write a User model.
Summary - Data class
In this group you learned the data class definition, copying with copy, automatic equals and hashCode, the toString format and splitting into components with destructuring.
Now you will combine them: define a data class, modify it with copy and split it with destructuring. This structure is the foundation of data modeling and transfer in Kotlin. Later, sealed classes and generics will build on it.
Practice Combine the User model
Define a data class named User with a primary constructor taking val name: String, val age: Int, val email: String. In main create a User("Alex", 30, "alex@x.com") instance. Produce a v instance with u.copy(age = 31). Split u into name, age and email with destructuring. Print name, age and v separately with println.
Starter code
// Define the User data class
// with name, age, email properties
// instantiate, produce v via copy
// split with destructuring, print all threeSample solution
data class User(val name: String, val age: Int, val email: String)
fun main() {
val u = User("Alex", 30, "alex@x.com")
val v = u.copy(age = 31)
val (name, age, email) = u
println(name)
println(age)
println(v)
}Expected output
Alex 30 User(name=Alex, age=31, email=alex@x.com)
What comes next?
You learned data classes. In the next groups you will explore closed hierarchies with sealed classes, exhaustive branching with when and singletons with object.
This group combined data class, copy, equals, toString and destructuring. These are the core of Kotlin data modeling. Next you will see safe inheritance patterns with closed hierarchies.
Practice The Money data class with an add method
Define a data class named Money with a primary constructor taking val amount: Double, val currency: String. Add a method fun add(other: Money): Money whose body returns Money(amount + other.amount, currency). In main create Money(100.0, "USD") and Money(50.0, "USD") instances, sum them with add and print the result.
Starter code
// Define the Money data class
// with amount and currency properties
// add method: sums with another Money
// create two instances, sum and print in mainSample solution
data class Money(val amount: Double, val currency: String) {
fun add(other: Money): Money {
return Money(amount + other.amount, currency)
}
}
fun main() {
val a = Money(100.0, "USD")
val b = Money(50.0, "USD")
val c = a.add(b)
println(c)
}Expected output
Money(amount=150.0, currency=USD)
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which of the following is not auto-generated in a data class?
- equals
- hashCode
- toString
- factory method Correct answer
Explanation: A factory method is not auto-generated; you write it yourself in a companion object.
2 Complete the copy call
val v = u.____(age = 31)val v = u.copy(age = 31)Explanation: The copy method produces a clone with changed properties.