Constant values with const val in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing const val in Kotlin

What is the output of this Kotlin code snippet?

Kotlin

object Constants {
    const val PI = 3.14
}

fun main() {
    println(Constants.PI)
}

A 3.14

B PI

C Compilation error

D 0.0

💡 Hint

const val values are compile-time constants and can be accessed directly.

The const val PI is a compile-time constant and can be accessed directly without an instance. The println prints 3.14.

❓ Predict Output

intermediate

Value of const val in companion object

What will this Kotlin program print?

Kotlin

class Circle {
    companion object {
        const val RADIUS = 5
    }
}

fun main() {
    println(Circle.RADIUS)
}

A Runtime error

B RADIUS

C null

D 5

💡 Hint

const val in companion object acts like a static constant.

The const val RADIUS is accessible via the class name and prints 5.

❓ Predict Output

advanced

Effect of const val on memory usage

Consider this Kotlin code. What is the output?

Kotlin

object Config {
    const val MAX_USERS = 1000
    val maxUsersRuntime = 1000
}

fun main() {
    println(Config.MAX_USERS === Config.maxUsersRuntime)
}

A true

B Compilation error

C false

D Runtime exception

💡 Hint

const val is a primitive compile-time constant, val is a runtime object.

MAX_USERS is a primitive constant, maxUsersRuntime is an object. === compares references, so false.

❓ Predict Output

advanced

Compilation error with const val usage

What error does this Kotlin code produce?

Kotlin

class Test {
    const val number = 10
}

fun main() {
    println(Test().number)
}

A Modifier 'const' is not allowed here

B Unresolved reference: number

C No error, prints 10

D Runtime exception

💡 Hint

const val can only be declared at top-level or in object/companion object.

const val cannot be declared as a member property of a regular class. It must be in object or companion object.

🧠 Conceptual

expert

Why use const val instead of val in Kotlin?

Which statement best explains the advantage of using const val over val in Kotlin?

A const val allows changing the value at runtime for flexibility

B const val values are inlined at compile time, improving performance and allowing usage in annotations

C val variables are always compile-time constants, const val is redundant

D const val can only be used inside functions, val cannot

💡 Hint

Think about when the value is fixed and how Kotlin uses it internally.

const val is a compile-time constant, so its value is inlined and can be used in annotations. val is a runtime constant and cannot be used in annotations.