Terminal operations trigger execution in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to trigger execution of the sequence with a terminal operation.

Kotlin

val numbers = sequenceOf(1, 2, 3, 4)
numbers.[1]()

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

AtoList

Bmap

Cfilter

Dtake

Attempts:

3 left

💡 Hint

Common Mistakes

Using intermediate operations like map or filter which do not trigger execution.

The toList() function is a terminal operation that triggers the execution of the sequence and collects the results into a list.

2fill in blank

medium

Complete the code to print the first element of the sequence, triggering execution.

Kotlin

val seq = sequenceOf("a", "b", "c")
println(seq.[1]())

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

Afirst

Bmap

Cfilter

Ddrop

Attempts:

3 left

💡 Hint

Common Mistakes

Using intermediate operations like map or filter which do not trigger execution.

The first() function is a terminal operation that triggers execution and returns the first element.

3fill in blank

hard

Fix the error in the code by choosing the correct terminal operation to trigger execution.

Kotlin

val seq = sequenceOf(10, 20, 30)
val sum = seq.[1] { acc, i -> acc + i }

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

Amap

Breduce

Cfilter

Dtake

Attempts:

3 left

💡 Hint

Common Mistakes

Using intermediate operations like map or filter which do not trigger execution.

The reduce function is a terminal operation that aggregates the sequence elements and triggers execution.

4fill in blank

hard

Fill both blanks to collect even numbers from the sequence into a list, triggering execution.

Kotlin

val seq = sequenceOf(1, 2, 3, 4, 5)
val evens = seq.[1] { it % 2 == 0 }.[2]()

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

Afilter

Bmap

CtoList

Dtake

Attempts:

3 left

💡 Hint

Common Mistakes

Using only intermediate operations without a terminal operation.

filter selects even numbers (intermediate operation), and toList collects them into a list (terminal operation) triggering execution.

5fill in blank

hard

Fill all three blanks to transform, filter, and collect sequence elements, triggering execution.

Kotlin

val seq = sequenceOf("apple", "banana", "cherry")
val result = seq.[1] { it.length }.[2] { it > 5 }.[3]()

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

Amap

Bfilter

CtoList

Dtake

Attempts:

3 left

💡 Hint

Common Mistakes

Using terminal operations too early, or missing the terminal operation.

map transforms strings to their lengths, filter selects lengths greater than 5, and toList collects results, triggering execution.

Practice

1. What does a terminal operation do in Kotlin sequences or collections?
toList(), count(), and forEach() are examples of terminal operations. What is their main role?

easy

A. They start the actual processing and produce results or side effects.

B. They define the data source without processing it.

C. They create new sequences without executing any code.

D. They only prepare the data but do not execute any operation.

Solution

1. Step 1: Understand what terminal operations are

   Terminal operations are the final step in a sequence or collection processing chain that triggers execution.

2. Step 2: Identify the role of examples like toList(), count(), and forEach()

   These operations produce a result or cause side effects, thus starting the actual processing.

3. Final Answer:

   They start the actual processing and produce results or side effects. -> Option A

4. Quick Check:

   Terminal operations trigger execution = B [OK]

Hint: Terminal operations always trigger execution and produce results [OK]

Common Mistakes:

• Thinking terminal operations only prepare data without running it
• Confusing terminal operations with intermediate operations
• Believing terminal operations do not produce results

2. Which of the following is a correct Kotlin terminal operation syntax on a list named numbers?

easy

A. numbers.toList()

B. numbers.map()

C. numbers.filter()

D. numbers.sortedBy

Solution

1. Step 1: Identify terminal operations syntax

   Terminal operations like toList() are called with parentheses to execute and produce results.

2. Step 2: Check each option

   map() and filter() are intermediate operations requiring arguments; sortedBy is incomplete without parentheses.

3. Final Answer:

   numbers.toList() -> Option A

4. Quick Check:

   Correct terminal operation syntax = A [OK]

Hint: Terminal operations have parentheses and produce results [OK]

Common Mistakes:

• Using intermediate operations as terminal without arguments
• Omitting parentheses on function calls
• Confusing intermediate and terminal operations

3. Consider this Kotlin code:

val numbers = sequenceOf(1, 2, 3, 4)
val result = numbers.filter { it % 2 == 0 }.count()

What is the value of result after execution?

medium

A. 0

B. 4

C. 2

D. Sequence<Int>

Solution

1. Step 1: Apply the filter condition

   The filter keeps only even numbers: 2 and 4.

2. Step 2: Count the filtered elements

   There are 2 even numbers, so count() returns 2.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   Count of even numbers = 2 [OK]

Hint: Filter then count gives number of matching elements [OK]

Common Mistakes:

• Counting before filtering
• Assuming count returns the sequence itself
• Confusing sequence with list output

4. What is wrong with this Kotlin code snippet?

val numbers = listOf(1, 2, 3)
numbers.filter { it > 1 }

Why does it not print or return any filtered list?

medium

A. The variable numbers is immutable.

B. Missing a terminal operation to trigger execution.

C. List cannot be filtered in Kotlin.

D. The filter condition is invalid syntax.

Solution

1. Step 1: Understand filter is intermediate

   The filter function returns a new list but does not execute anything by itself.

2. Step 2: Identify missing terminal operation

   Without a terminal operation like toList() or forEach(), the filtered list is not processed or printed.

3. Final Answer:

   Missing a terminal operation to trigger execution. -> Option B

4. Quick Check:

   Intermediate operations need terminal to run = D [OK]

Hint: Always end with terminal operation to see results [OK]

Common Mistakes:

• Thinking filter runs immediately
• Assuming immutability blocks filtering
• Believing filter syntax is wrong

5. Given this Kotlin code:

val data = sequenceOf(0, 1, 2, 3, 4, 5)
val result = data
  .filter { it > 0 }
  .map { if (it % 2 == 0) it * 10 else it }
  .toList()

What is the content of result after execution?

hard

A. [10, 20, 30, 40, 50]

B. [0, 1, 2, 3, 4, 5]

C. [1, 2, 3, 4, 5]

D. [1, 20, 3, 40, 5]

Solution

1. Step 1: Filter out values greater than 0

   Sequence after filter: 1, 2, 3, 4, 5 (0 is removed).

2. Step 2: Map even numbers to value * 10, odd numbers unchanged

   1 (odd) -> 1, 2 (even) -> 20, 3 (odd) -> 3, 4 (even) -> 40, 5 (odd) -> 5.

3. Step 3: Convert sequence to list with toList()

   Final list: [1, 20, 3, 40, 5].

4. Final Answer:

   [1, 20, 3, 40, 5] -> Option D

5. Quick Check:

   Filter then map then toList = C [OK]

Hint: Filter first, then map, then terminal operation to get result [OK]

Common Mistakes:

• Forgetting filter removes 0
• Mapping all numbers instead of only even
• Missing toList() to trigger execution