List creation (listOf, mutableListOf) in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code?

Consider the following Kotlin code snippet. What will be printed?

Kotlin

val list = listOf(1, 2, 3)
println(list.size)
println(list[1])

A 3\n2

B 2\n1

C 3\n1

D 2\n3

💡 Hint

Remember that listOf creates an immutable list and indexing starts at 0.

The list has 3 elements: 1, 2, and 3. The size is 3. The element at index 1 is the second element, which is 2.

❓ Predict Output

intermediate

What happens when you try to add an element to a listOf list?

What will happen when running this Kotlin code?

Kotlin

val list = listOf(10, 20, 30)
list.add(40)

A Runtime exception: UnsupportedOperationException

B Compilation error: val cannot be reassigned

C The element 40 is added successfully

D Compilation error: Unresolved reference 'add'

💡 Hint

listOf creates an immutable list without add method.

listOf returns an immutable list which does not have an add method. Trying to call add causes a compilation error because the method does not exist.

❓ Predict Output

advanced

What is the output of this Kotlin code using mutableListOf?

Analyze the following Kotlin code and select the output:

Kotlin

val mutableList = mutableListOf("a", "b")
mutableList.add("c")
println(mutableList.size)
println(mutableList[2])

A 3\nb

B 2\nc

C 3\nc

D RuntimeException: IndexOutOfBoundsException

💡 Hint

mutableListOf creates a list you can change by adding elements.

The mutable list starts with 2 elements. After adding "c", size becomes 3. The element at index 2 is "c".

🧠 Conceptual

advanced

Which statement about listOf and mutableListOf is true?

Choose the correct statement about Kotlin's listOf and mutableListOf functions.

A listOf creates a mutable list; mutableListOf creates an immutable list

B listOf creates an immutable list; mutableListOf creates a mutable list

C Both listOf and mutableListOf create immutable lists

D Both listOf and mutableListOf create mutable lists

💡 Hint

Think about whether you can add or remove elements after creation.

listOf creates a list that cannot be changed after creation (immutable). mutableListOf creates a list that can be changed (mutable).

❓ Predict Output

expert

What is the output of this Kotlin code involving list creation and modification?

Examine this Kotlin code and select the output:

Kotlin

val list1 = listOf(1, 2, 3)
val list2 = list1.toMutableList()
list2.add(4)
println(list1.size)
println(list2.size)

A 3\n4

B 4\n4

C 3\n3

D RuntimeException: UnsupportedOperationException

💡 Hint

toMutableList creates a new mutable copy of the original list.

list1 is immutable with size 3. list2 is a mutable copy, so after adding 4, its size is 4. list1 remains size 3.

Practice

1. Which Kotlin function creates a list that cannot be changed after it is created?

easy

A. listOf

B. mutableListOf

C. arrayListOf

D. setOf

Solution

1. Step 1: Understand listOf behavior

   listOf creates a fixed list that cannot be changed after creation.

2. Step 2: Compare with mutableListOf

   mutableListOf creates a list that can be changed (add/remove items).

3. Final Answer:

   listOf -> Option A

4. Quick Check:

   Fixed list = listOf [OK]

Hint: Use listOf for fixed lists, mutableListOf for changeable lists [OK]

Common Mistakes:

• Confusing mutableListOf as fixed list
• Thinking arrayListOf is immutable
• Using setOf which creates a set, not a list

2. Which of the following is the correct syntax to create a mutable list of integers with values 1, 2, and 3?

easy

A. val list = listOf(1, 2, 3)

B. val list = mutableListOf(1, 2, 3)

C. val list = mutableList(1, 2, 3)

D. val list = list(1, 2, 3)

Solution

1. Step 1: Identify correct function name

   The correct function to create a mutable list is mutableListOf.

2. Step 2: Check syntax correctness

   Options C and D use invalid function names. val list = listOf(1, 2, 3) creates an immutable list.

3. Final Answer:

   val list = mutableListOf(1, 2, 3) -> Option B

4. Quick Check:

   Mutable list syntax = mutableListOf(...) [OK]

Hint: Remember mutableListOf has 'Of' at the end [OK]

Common Mistakes:

• Using listOf instead of mutableListOf for mutable lists
• Misspelling mutableListOf as mutableList
• Using list() which does not exist

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

val list = listOf("apple", "banana", "cherry")
println(list[1])

medium

A. banana

B. IndexOutOfBoundsException

C. cherry

D. apple

Solution

1. Step 1: Understand list indexing

   Kotlin lists use zero-based indexing, so index 1 refers to the second item.

2. Step 2: Identify the item at index 1

   The list is ["apple", "banana", "cherry"], so index 1 is "banana".

3. Final Answer:

   banana -> Option A

4. Quick Check:

   Index 1 = second item = banana [OK]

Hint: Remember list indexes start at 0 in Kotlin [OK]

Common Mistakes:

• Thinking index 1 is the first item
• Expecting an error for valid index
• Confusing listOf with mutableListOf output

4. What is wrong with this Kotlin code?

val list = listOf(1, 2, 3)
list.add(4)

medium

A. add() method requires a mutableListOf list

B. Syntax error in listOf declaration

C. listOf creates an immutable list; add() is not allowed

D. No error; code runs fine

Solution

1. Step 1: Check list type

   listOf creates an immutable (read-only) list.

2. Step 2: Understand add() method

   The add() method is only available on mutable lists, not on immutable lists.

3. Final Answer:

   listOf creates an immutable list; add() is not allowed -> Option C

4. Quick Check:

   Immutable list cannot add items [OK]

Hint: Use mutableListOf to add or remove items [OK]

Common Mistakes:

• Trying to add to listOf list
• Ignoring immutability of listOf
• Assuming add() works on all lists

5. You want to create a list of strings that you can add items to later. Which Kotlin code correctly creates this list and adds "orange" to it?

hard

A. val fruits = mutableListOf("apple", "banana")
fruits = fruits + "orange"

B. val fruits = listOf("apple", "banana")
fruits.add("orange")

C. val fruits = listOf("apple", "banana")
fruits += "orange"

D. val fruits = mutableListOf("apple", "banana")
fruits.add("orange")

Solution

1. Step 1: Choose a mutable list

   To add items later, the list must be mutable, so use mutableListOf.

2. Step 2: Use add() method correctly

   Calling add("orange") on a mutable list adds the item successfully.

3. Step 3: Check other options

   val fruits = listOf("apple", "banana") fruits.add("orange") tries to add to immutable list (error). val fruits = listOf("apple", "banana") fruits += "orange" uses += on immutable list (creates new list but does not modify original). val fruits = mutableListOf("apple", "banana") fruits = fruits + "orange" tries to reassign val which is not allowed.

4. Final Answer:

   val fruits = mutableListOf("apple", "banana") fruits.add("orange") -> Option D

5. Quick Check:

   Mutable list + add() = correct way [OK]

Hint: Use mutableListOf and add() to change list after creation [OK]

Common Mistakes:

• Adding to immutable list
• Trying to reassign val variable
• Using += on immutable list expecting mutation