RunCatching for safe execution in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to safely execute the block using RunCatching.

Kotlin

val result = runCatching([1] {
    val number = "123".toInt()
    number * 2
})

Drag options to blanks, or click blank then click option'

A{}

B()

C() ->

D() -> Unit

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect lambda syntax like () -> Unit or {} which are not valid here.

The runCatching function takes a lambda with no parameters, so we use () -> before the lambda block.

2fill in blank

medium

Complete the code to get the result value or null if an exception occurs.

Kotlin

val result = runCatching {
    "abc".toInt()
}.[1]()

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AgetOrNull

BgetOrThrow

CgetOrDefault

DgetOrElse

Attempts:

3 left

💡 Hint

Common Mistakes

Using getOrThrow() which throws the exception instead of returning null.

getOrNull() returns the value if successful or null if an exception was caught.

3fill in blank

hard

Fix the error in the code to handle failure with onFailure.

Kotlin

runCatching {
    val x = 10 / 0
}.[1] {
    println("Error: ${it.message}")
}

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AonSuccess

BonFailure

CgetOrNull

DgetOrElse

Attempts:

3 left

💡 Hint

Common Mistakes

Using onSuccess which runs only if no exception occurred.

onFailure is used to handle exceptions caught by runCatching.

4fill in blank

hard

Fill both blanks to create a map of word lengths only for words longer than 3 characters.

Kotlin

val words = listOf("cat", "house", "dog", "elephant")
val lengths = words.associateWith { [1] }
    .filter { it.value [2] 3 }

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Ait.length

B>

C<

Dit.size

Attempts:

3 left

💡 Hint

Common Mistakes

Using it.size which is invalid for String.

Using < instead of > in filter condition.

Use it.length to get word length and filter with > 3 to keep longer words.

5fill in blank

hard

Fill all three blanks to safely get uppercase words longer than 4 characters.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val safeWords = runCatching {
    words.map { it.[1]() }
}.getOrElse { emptyList() }
.filter { it.length [2] 4 }
.associateWith { it.length [3] 0 }

Drag options to blanks, or click blank then click option'

Auppercase

B>

C*

Duppercase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase without parentheses which is not a function call.

Using < instead of > in filter.

Using + or - instead of * in multiplication.

Use uppercase() to convert words, filter length > 4, and multiply length by 0 to get 0.

Practice

1. What is the main purpose of runCatching in Kotlin?

easy

A. To execute code and catch exceptions safely without crashing the program

B. To run code only if a condition is true

C. To create a new thread for running code

D. To convert a value to a string safely

Solution

1. Step 1: Understand what runCatching does

   runCatching runs a block of code and catches any exceptions that happen inside it.

2. Step 2: Identify the main purpose

   This helps keep the program running smoothly by handling errors safely without crashing.

3. Final Answer:

   To execute code and catch exceptions safely without crashing the program -> Option A

4. Quick Check:

   runCatching = safe execution [OK]

Hint: runCatching catches errors to keep code safe [OK]

Common Mistakes:

• Thinking runCatching runs code conditionally
• Confusing runCatching with threading
• Assuming it converts types automatically

2. Which of the following is the correct syntax to use runCatching in Kotlin?

easy

A. val result = runCatching -> someFunction()

B. val result = runCatching(someFunction())

C. val result = runCatching { someFunction() }

D. val result = runCatching.someFunction()

Solution

1. Step 1: Recall the syntax of runCatching

   runCatching takes a lambda block with curly braces to run code safely.

2. Step 2: Match the correct syntax

   val result = runCatching { someFunction() } uses curly braces and calls someFunction() inside, which is correct.

3. Final Answer:

   val result = runCatching { someFunction() } -> Option C

4. Quick Check:

   runCatching uses braces { } [OK]

Hint: Use curly braces {} to pass code block to runCatching [OK]

Common Mistakes:

• Using parentheses instead of braces
• Trying to call runCatching like a function with arrow
• Accessing runCatching as an object

3. What will be the output of this Kotlin code?

val result = runCatching { 10 / 0 }
println(result.isSuccess)

medium

A. true

B. null

C. Exception thrown

D. false

Solution

1. Step 1: Analyze the code inside runCatching

   The code tries to divide 10 by 0, which causes an exception (ArithmeticException).

2. Step 2: Understand runCatching result

   runCatching catches the exception, so no crash happens. The isSuccess property will be false because the block failed.

3. Final Answer:

   false -> Option D

4. Quick Check:

   Exception caught means isSuccess = false [OK]

Hint: Divide by zero causes failure, so isSuccess is false [OK]

Common Mistakes:

• Expecting true because code runs
• Thinking exception is thrown outside runCatching
• Confusing isSuccess with isFailure

4. Identify the error in this Kotlin code using runCatching:

val result = runCatching {
    val number = "abc".toInt()
}
println(result.getOrNull())

medium

A. No error, prints null because conversion fails

B. Throws NumberFormatException outside runCatching

C. Syntax error in runCatching block

D. getOrNull() returns the string "abc"

Solution

1. Step 1: Understand the code inside runCatching

   Trying to convert "abc" to Int causes NumberFormatException, but runCatching catches it.

2. Step 2: Check what getOrNull() returns

   Since exception happened, getOrNull() returns null safely without crashing.

3. Final Answer:

   No error, prints null because conversion fails -> Option A

4. Quick Check:

   Exception caught means getOrNull() = null [OK]

Hint: runCatching catches exceptions, getOrNull returns null on failure [OK]

Common Mistakes:

• Expecting exception to crash program
• Thinking getOrNull returns original string
• Assuming syntax error in code block

5. You want to safely parse a list of strings to integers using runCatching and collect only the successful results. Which Kotlin code snippet correctly does this?

hard

A. val numbers = list.map { runCatching { it.toInt() }.exceptionOrNull() }

B. val numbers = list.map { runCatching { it.toInt() }.getOrNull() }.filterNotNull()

C. val numbers = list.map { it.toInt() }.filter { it != null }

D. val numbers = list.map { runCatching { it.toInt() }.getOrThrow() }

Solution

1. Step 1: Understand the goal

   We want to convert strings to integers safely, ignoring failures, and collect only successful integers.

2. Step 2: Analyze each option

   val numbers = list.map { runCatching { it.toInt() }.getOrNull() }.filterNotNull() uses runCatching to catch exceptions, then getOrNull() returns integer or null, and filterNotNull() removes nulls, collecting only successful parses.

3. Final Answer:

   val numbers = list.map { runCatching { it.toInt() }.getOrNull() }.filterNotNull() -> Option B

4. Quick Check:

   Safe parse + filter null = val numbers = list.map { runCatching { it.toInt() }.getOrNull() }.filterNotNull() [OK]

Hint: Use getOrNull() then filterNotNull() to keep successful parses [OK]

Common Mistakes:

• Using getOrThrow() which throws on failure
• Filtering nulls before catching exceptions
• Using exceptionOrNull() which returns exceptions, not values