Try-catch as an expression in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of try-catch expression with successful try block

What is the output of this Kotlin code snippet?

Kotlin

val result = try {
    val x = 10 / 2
    "Success: $x"
} catch (e: ArithmeticException) {
    "Error"
}
println(result)

A Success: 5

B Error

C 10

D Compilation error

💡 Hint

Remember that try-catch in Kotlin can return a value from the try block if no exception occurs.

The try block executes successfully without exceptions, so the expression returns "Success: 5".

❓ Predict Output

intermediate

Output when exception is thrown in try block

What will be printed by this Kotlin code?

Kotlin

val result = try {
    val x = 10 / 0
    "Success: $x"
} catch (e: ArithmeticException) {
    "Error caught"
}
println(result)

A Success: 0

B Error caught

C ArithmeticException thrown

D Compilation error

💡 Hint

Division by zero throws an exception, so the catch block runs.

The division by zero causes an ArithmeticException, so the catch block returns "Error caught".

❓ Predict Output

advanced

Value of variable after try-catch expression with finally

What is the value of variable 'result' after running this Kotlin code?

Kotlin

val result = try {
    "Try block"
} catch (e: Exception) {
    "Catch block"
} finally {
    println("Finally block executed")
}
println(result)

A Compilation error

B Catch block

C null

D Try block

💡 Hint

Finally block runs but does not affect the returned value.

The try block returns "Try block". The finally block runs but does not change the result.

❓ Predict Output

advanced

Output when catch block throws exception in try-catch expression

What happens when this Kotlin code runs?

Kotlin

val result = try {
    val x = 10 / 0
    "Success"
} catch (e: ArithmeticException) {
    throw IllegalStateException("New exception")
}
println(result)

A IllegalStateException is thrown

B Success

C Compilation error

D ArithmeticException is caught and printed

💡 Hint

The catch block throws a new exception instead of returning a value.

The try block throws ArithmeticException, caught by catch, which then throws IllegalStateException. No value is returned.

🧠 Conceptual

expert

Why is try-catch an expression in Kotlin?

Which statement best explains why try-catch is an expression in Kotlin?

A Because it can only be used inside functions that return Unit.

B Because it only handles exceptions without returning any value.

C Because it can return a value from either the try or catch block, allowing assignment to variables.

D Because it requires a finally block to compile successfully.

💡 Hint

Think about how try-catch can be used in assignments.

In Kotlin, try-catch is an expression that returns a value from either the try or catch block, enabling concise error handling and assignment.

Practice

1. What does it mean that try-catch is an expression in Kotlin?

easy

A. It can only be used inside functions with no return type.

B. It only catches exceptions but cannot return values.

C. It must always be followed by a finally block.

D. It can return a value that can be assigned to a variable.

Solution

1. Step 1: Understand try-catch as an expression

   In Kotlin, try-catch can produce a value, unlike in some languages where it is only a statement.

2. Step 2: Recognize value assignment

   This means you can assign the result of a try-catch block directly to a variable.

3. Final Answer:

   It can return a value that can be assigned to a variable. -> Option D

4. Quick Check:

   Try-catch returns value = D [OK]

Hint: Try-catch can be assigned like any expression [OK]

Common Mistakes:

• Thinking try-catch cannot return values
• Confusing try-catch with only statements
• Believing finally is always required

2. Which of the following is the correct syntax to assign a value using try-catch as an expression in Kotlin?

easy

A. val result = try { 10 / 0 } catch (e: Exception) { 0 }

B. val result try { 10 / 0 } catch (e: Exception) { 0 }

C. val result = try { 10 / 0 } finally { 0 }

D. val result = catch (e: Exception) { 0 } try { 10 / 0 }

Solution

1. Step 1: Check assignment syntax

   The correct way to assign a value from try-catch is using val result = try { ... } catch { ... }.

2. Step 2: Validate each option

   val result = try { 10 / 0 } catch (e: Exception) { 0 } uses correct syntax with try-catch returning a value. Options A, B, and D have syntax errors or misuse of finally/catch.

3. Final Answer:

   val result = try { 10 / 0 } catch (e: Exception) { 0 } -> Option A

4. Quick Check:

   Correct try-catch assignment syntax = C [OK]

Hint: Remember: val x = try { } catch { } [OK]

Common Mistakes:

• Omitting '=' in assignment
• Using finally block to return value
• Placing catch before try

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

val result = try {
    val num = 10 / 2
    "Success: $num"
} catch (e: Exception) {
    "Error"
}
println(result)

medium

A. Error

B. Success: 5

C. 10 / 2

D. Exception thrown

Solution

1. Step 1: Evaluate try block

   The division 10 / 2 equals 5, so the try block returns the string "Success: 5".

2. Step 2: Check for exceptions

   No exception occurs, so the catch block is skipped.

3. Final Answer:

   Success: 5 -> Option B

4. Quick Check:

   Try succeeds, output = Success: 5 [OK]

Hint: If no error, try block value is returned [OK]

Common Mistakes:

• Assuming catch runs even without error
• Printing the expression instead of result
• Confusing integer division with string output

4. Identify the error in this Kotlin code using try-catch as an expression:

val result = try {
    val x = 10 / 0
    x
} catch {
    0
}
println(result)

medium

A. Cannot assign try-catch to a val

B. Division by zero is allowed without catch

C. Missing exception parameter in catch block

D. println cannot print variables from try-catch

Solution

1. Step 1: Check catch block syntax

   The catch block must declare an exception parameter like catch (e: Exception).

2. Step 2: Identify the error

   Here, catch is missing the exception parameter, causing a syntax error.

3. Final Answer:

   Missing exception parameter in catch block -> Option C

4. Quick Check:

   Catch needs exception parameter = B [OK]

Hint: Always include exception variable in catch (e: Exception) [OK]

Common Mistakes:

• Omitting exception parameter in catch
• Ignoring division by zero error
• Thinking try-catch can't be assigned

5. Given this Kotlin function using try-catch as an expression, what will parseIntOrZero("abc") return?

fun parseIntOrZero(input: String): Int = try {
    input.toInt()
} catch (e: NumberFormatException) {
    0
}

hard

A. Returns 0

B. Throws NumberFormatException

C. Returns null

D. Returns input string

Solution

1. Step 1: Analyze try block behavior

   Calling input.toInt() on "abc" throws NumberFormatException.

2. Step 2: Catch block returns fallback

   The catch block catches this exception and returns 0 as fallback.

3. Final Answer:

   Returns 0 -> Option A

4. Quick Check:

   Exception caught, fallback 0 returned = A [OK]

Hint: Catch returns fallback value on error [OK]

Common Mistakes:

• Expecting exception to propagate
• Thinking null is returned on error
• Confusing return type with input type