Why Kotlin over Java - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using null safety?

Consider this Kotlin code snippet that uses null safety features. What will it print?

Kotlin

fun main() {
    val name: String? = null
    val length = name?.length ?: -1
    println(length)
}

A 0

B -1

C Throws NullPointerException

D null

💡 Hint

Look at the Elvis operator ?: and how it handles null values.

The variable name is nullable and set to null. The safe call operator ?. returns null for name?.length. The Elvis operator ?: then provides -1 as a default value. So, length becomes -1.

🧠 Conceptual

intermediate

Why does Kotlin reduce boilerplate compared to Java?

Which Kotlin feature helps reduce the amount of boilerplate code compared to Java?

A Kotlin forces manual memory management

B Kotlin requires explicit getters and setters for all properties

C Kotlin does not support lambdas

D Data classes automatically generate common methods like equals and toString

💡 Hint

Think about how Kotlin handles simple classes with properties.

Kotlin's data classes automatically generate equals(), hashCode(), toString(), and copy methods, reducing the need to write repetitive code.

🔧 Debug

advanced

Identify the error in this Kotlin code using coroutines

What error will this Kotlin coroutine code produce when run?

Kotlin

import kotlinx.coroutines.*

fun main() {
    GlobalScope.launch {
        delay(1000L)
        println("World!")
    }
    println("Hello,")
}

A Prints "Hello," only because main exits before coroutine runs

B Prints "Hello," then "World!" after 1 second

C Compilation error due to missing runBlocking

D Runtime exception: CoroutineScope not initialized

💡 Hint

Consider what happens to the main thread after launching a coroutine.

The main function launches a coroutine but does not wait for it. The program exits immediately, so "World!" is never printed.

📝 Syntax

advanced

Which Kotlin syntax correctly declares a read-only list?

Choose the correct Kotlin syntax to declare a read-only list of integers containing 1, 2, and 3.

A val list = listOf(1, 2, 3)

B val list = mutableListOf(1, 2, 3)

C val list = arrayListOf(1, 2, 3)

D val list = List(1, 2, 3)

💡 Hint

Read-only lists use a specific Kotlin function.

listOf() creates an immutable (read-only) list. mutableListOf() and arrayListOf() create mutable lists. List(1, 2, 3) is invalid syntax.

🚀 Application

expert

What is the output of this Kotlin code using sealed classes?

Given the sealed class hierarchy below, what will be printed when calling describeShape with a Circle(5.0)?

Kotlin

sealed class Shape
class Circle(val radius: Double) : Shape()
class Rectangle(val width: Double, val height: Double) : Shape()

fun describeShape(shape: Shape): String = when(shape) {
    is Circle -> "Circle with radius ${shape.radius}"
    is Rectangle -> "Rectangle with width ${shape.width} and height ${shape.height}"
}

fun main() {
    println(describeShape(Circle(5.0)))
}

A Runtime error: Unhandled type

B Rectangle with width 5.0 and height 5.0

C Circle with radius 5.0

D Compilation error: when expression is not exhaustive

💡 Hint

Sealed classes allow exhaustive when expressions without else.

The when expression covers all subclasses of Shape. Passing a Circle(5.0) matches the first case and prints the radius.