RunCatching for safe execution in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this RunCatching example?

Consider this Kotlin code using runCatching. What will it print?

Kotlin

val result = runCatching {
    val number = "123a".toInt()
    number * 2
}.getOrElse {
    -1
}
println(result)

A Exception in thread "main" java.lang.NumberFormatException

B 0

C -1

D 246

💡 Hint

Think about what happens when toInt() fails inside runCatching.

The string "123a" cannot be converted to an integer, so toInt() throws a NumberFormatException. The runCatching catches this exception, and getOrElse returns the fallback value -1.

❓ Predict Output

intermediate

What does this runCatching block return?

Analyze this Kotlin snippet using runCatching. What is the value of output?

Kotlin

val output = runCatching {
    val list = listOf(1, 2, 3)
    list[5]
}.getOrNull()
println(output)

A IndexOutOfBoundsException

B null

C 3

D 5

💡 Hint

What happens when you access an invalid index inside runCatching?

Accessing list[5] throws an IndexOutOfBoundsException. runCatching catches it, so getOrNull() returns null.

🔧 Debug

advanced

Why does this runCatching block not catch the exception?

Look at this Kotlin code. Why does the exception still crash the program?

Kotlin

val result = runCatching {
    throw IllegalStateException("Error happened")
}.getOrElse {
    throw it
}
println("Done")

A Because getOrElse rethrows the exception, so it is not handled.

B Because println("Done") is unreachable and causes a compile error.

C Because the exception is thrown outside runCatching block.

D Because runCatching only catches IOException, not IllegalStateException.

💡 Hint

Check what getOrElse does with the caught exception.

The runCatching catches the exception, but getOrElse rethrows it with throw it. So the exception is not handled and crashes the program.

📝 Syntax

advanced

Which option correctly uses runCatching to safely parse an integer?

Choose the Kotlin code snippet that safely parses a string to an integer using runCatching and returns 0 if parsing fails.

A val number = runCatching { "42".toInt() }.getOrElse { 0 }

B val number = runCatching { "42".toInt() } ?: 0

C val number = runCatching { "42".toInt() }.getOrDefault(0)

D val number = runCatching { "42".toInt() }.getOrNull() ?: 0

💡 Hint

Remember how getOrElse works compared to getOrDefault and getOrNull.

getOrElse returns the result if successful, or the lambda value if an exception occurred. ?: operator does not work directly on Result. getOrNull returns null on failure, so the Elvis operator works but returns null if success is null.

🚀 Application

expert

How many items are in the list after this runCatching chain?

Given this Kotlin code, how many items does results contain after execution?

Kotlin

val inputs = listOf("10", "abc", "20", "-5")
val results = inputs.mapNotNull { input ->
    runCatching { input.toInt() }
        .getOrNull()
}.filter { it > 0 }

A 3

B 1

C 4

D 2

💡 Hint

Count how many strings convert to positive integers successfully.

"10" and "20" convert successfully to positive integers. "abc" fails and returns null, "-5" converts but is filtered out because it is not > 0. So the final list has 2 items.