Data classes for value holders in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of data class copy with modification

What is the output of this Kotlin code using a data class and the copy function?

Kotlin

data class Point(val x: Int, val y: Int)

fun main() {
    val p1 = Point(3, 5)
    val p2 = p1.copy(y = 10)
    println(p2)
}

A Point(x=3, y=10)

B Point(x=3, y=5)

C Point(x=10, y=5)

D Compilation error

💡 Hint

The copy function creates a new instance with specified changes.

The copy function creates a new Point with the same x value and the new y value 10.

❓ Predict Output

intermediate

Equality check between data class instances

What will be the output of this Kotlin program?

Kotlin

data class User(val name: String, val age: Int)

fun main() {
    val user1 = User("Alice", 30)
    val user2 = User("Alice", 30)
    println(user1 == user2)
}

A true

B Runtime exception

C Compilation error

D false

💡 Hint

Data classes automatically implement equals based on properties.

Data classes compare all properties for equality, so user1 == user2 is true.

🔧 Debug

advanced

Why does this data class fail to compile?

This Kotlin data class code fails to compile. What is the cause?

Kotlin

data class Person(var name: String, val age: Int) {
    var name: String = name
}

A Missing primary constructor

B Data classes cannot have var properties

C Data classes cannot have properties with initializers

D Property 'name' is declared twice causing a conflict

💡 Hint

Check how properties are declared in the primary constructor and class body.

The property 'name' is declared in the constructor and again inside the class body, causing a duplicate declaration error.

🧠 Conceptual

advanced

Number of components in a data class

Given this Kotlin data class, how many component functions are generated automatically?

Kotlin

data class Rectangle(val width: Int, val height: Int, val color: String)

A 2

B 3

C 1

D 0

💡 Hint

Each property declared in the primary constructor generates a component function.

Each property (width, height, color) generates a component function: component1(), component2(), component3().

❓ Predict Output

expert

Output of destructuring declaration with data class

What is the output of this Kotlin program?

Kotlin

data class Book(val title: String, val author: String, val year: Int)

fun main() {
    val book = Book("1984", "Orwell", 1949)
    val (t, a, y) = book
    println("$t by $a, published in $y")
}

A Book(title=1984, author=Orwell, year=1949)

B Compilation error due to destructuring

C 1984 by Orwell, published in 1949

D Runtime exception

💡 Hint

Data classes support destructuring declarations matching their properties.

The destructuring declaration assigns each property to variables t, a, y, which are printed in the string.