Throw as an expression in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of throw as an expression in Kotlin

What is the output of this Kotlin code snippet?

Kotlin

fun test(value: Int): Int {
    val result = if (value > 0) value else throw IllegalArgumentException("Negative value")
    return result
}

fun main() {
    println(test(5))
}

A 5

B IllegalArgumentException thrown

C 0

D Compilation error

💡 Hint

Remember that throw can be used as an expression in Kotlin.

Since the value is 5 which is greater than 0, the if expression returns 5 and no exception is thrown.

❓ Predict Output

intermediate

Exception thrown with throw as expression

What happens when this Kotlin code runs?

Kotlin

fun test(value: Int): Int {
    val result = if (value > 0) value else throw IllegalArgumentException("Negative value")
    return result
}

fun main() {
    println(test(-1))
}

A Prints -1

B Prints 0

C Throws IllegalArgumentException with message "Negative value"

D Compilation error

💡 Hint

Check what happens when value is not greater than 0.

Since value is -1, the else branch throws an IllegalArgumentException with the given message.

🔧 Debug

advanced

Identify the error with throw as expression

Why does this Kotlin code cause a compilation error?

Kotlin

fun test(value: Int): Int {
    val result = if (value > 0) value else throw "Error"
    return result
}

A if expression must have else branch returning Int

B Variable result is not initialized

C Missing return statement

D throw must throw a Throwable, not a String

💡 Hint

Check the type of the expression after throw.

In Kotlin, throw must throw an object of type Throwable or its subclass, not a String.

🧠 Conceptual

advanced

Using throw as an expression in Elvis operator

What is the output of this Kotlin code?

Kotlin

fun test(value: String?): String {
    return value ?: throw IllegalArgumentException("Value required")
}

fun main() {
    println(test(null))
}

A Throws IllegalArgumentException with message "Value required"

B Prints null

C Prints empty string

D Compilation error

💡 Hint

Consider what the Elvis operator does when the left side is null.

The Elvis operator returns the left side if not null; otherwise, it evaluates the right side which throws an exception.

❓ Predict Output

expert

Throw as expression in complex return statement

What is the output of this Kotlin program?

Kotlin

fun parseIntOrThrow(input: String): Int {
    return input.toIntOrNull() ?: throw NumberFormatException("Invalid number")
}

fun main() {
    try {
        println(parseIntOrThrow("123"))
        println(parseIntOrThrow("abc"))
    } catch (e: NumberFormatException) {
        println(e.message)
    }
}

A 123\nException in thread "main" java.lang.NumberFormatException

B 123\nInvalid number

C Invalid number\n123

D Compilation error

💡 Hint

Check how the exception is caught and handled in main.

The first call prints 123. The second call throws NumberFormatException caught by catch block, printing the message.