Why Kotlin has no primitive types at source level - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable of type Int in Kotlin.

Kotlin

val number: [1] = 10

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

AprimitiveInt

BInt

Cint

DInteger

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'int' which is not valid in Kotlin source code.

In Kotlin, Int is used to declare integer variables. There are no primitive types like int at the source level.

2fill in blank

medium

Complete the code to create a list of integers in Kotlin.

Kotlin

val numbers = listOf(1, 2, 3).map { it [1] 2 }

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' which adds instead of multiplying.

The map function applies the operation to each element. Multiplying by 2 doubles each number.

3fill in blank

hard

Fix the error in the Kotlin function that returns the sum of two numbers.

Kotlin

fun sum(a: Int, b: Int): Int {
    return a [1] b
}

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

A/

B-

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' which subtracts instead of adding.

The function should return the sum, so the '+' operator is correct.

4fill in blank

hard

Fill both blanks to create a map of words to their lengths, filtering words longer than 3 characters.

Kotlin

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

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

A>

Blength

C<

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which filters shorter words.

Using 'count' which is a function, not a property.

The filter keeps words longer than 3 characters using '>'. The associateWith maps each word to its length property.

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths, filtering words with length greater than 4.

Kotlin

val words = listOf("apple", "bat", "carrot", "dog")
val result = words.filter { it.[1] [2] 4 }.associate { it.[3] to it.length }

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

Alength

B>

Cuppercase

Duppercase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'uppercase' without parentheses which is not a function call.

Using '<' instead of '>' for filtering.

Filter uses 'length' property and '>' operator. To convert to uppercase, use the function 'uppercase()'.

Practice

1. Why does Kotlin not show primitive types like int or float directly in its source code?

easy

A. Because Kotlin runs only on virtual machines without primitives

B. Because Kotlin does not support primitive types at all

C. To force developers to use only objects

D. To keep the language simple and safe for developers

Solution

1. Step 1: Understand Kotlin's design goal

   Kotlin aims to be simple and safe for developers by hiding complex details like primitives.

2. Step 2: Recognize how Kotlin handles primitives

   The compiler automatically converts Kotlin types to primitives behind the scenes for performance.

3. Final Answer:

   To keep the language simple and safe for developers -> Option D

4. Quick Check:

   Kotlin hides primitives for simplicity [OK]

Hint: Remember Kotlin hides primitives to keep code simple [OK]

Common Mistakes:

• Thinking Kotlin has no primitive types at all
• Believing primitives must be declared explicitly
• Assuming Kotlin only uses objects without optimization

2. Which of the following Kotlin declarations correctly shows how primitive types appear in Kotlin source code?

easy

A. val number: int = 10

B. val number: Integer = 10

C. val number: Int = 10

D. val number: primitiveInt = 10

Solution

1. Step 1: Recall Kotlin type naming conventions

   Kotlin uses capitalized type names like Int instead of lowercase int.

2. Step 2: Identify the correct syntax

   val number: Int = 10 is the correct Kotlin syntax for an integer variable.

3. Final Answer:

   val number: Int = 10 -> Option C

4. Quick Check:

   Kotlin uses capitalized types like Int [OK]

Hint: Kotlin types start with uppercase letters like Int [OK]

Common Mistakes:

• Using lowercase 'int' which is Java style
• Using 'Integer' which is Java boxed type
• Inventing types like 'primitiveInt' which don't exist

3. Consider this Kotlin code:

fun main() {
    val x: Int = 5
    val y: Int = 10
    println(x + y)
}

What will be the output when this code runs?

medium

A. 15

B. 510

C. x + y

D. Compilation error

Solution

1. Step 1: Understand variable types and values

   Both x and y are integers with values 5 and 10 respectively.

2. Step 2: Calculate the sum printed

   The expression x + y adds 5 + 10, resulting in 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Adding Int variables prints their sum, not concatenation [OK]

Common Mistakes:

• Thinking '+' concatenates like strings
• Expecting a compilation error due to primitives
• Confusing output with variable names

4. Identify the error in this Kotlin code snippet:

fun main() {
    val a: Int = null
    println(a)
}

medium

A. Incorrect print statement syntax

B. Cannot assign null to a non-nullable Int

C. Missing semicolon after declaration

D. Int type is not supported in Kotlin

Solution

1. Step 1: Check variable assignment rules

   In Kotlin, Int is non-nullable by default and cannot hold null.

2. Step 2: Identify the cause of error

   Assigning null to a causes a compilation error.

3. Final Answer:

   Cannot assign null to a non-nullable Int -> Option B

4. Quick Check:

   Non-nullable Int cannot be null [OK]

Hint: Non-nullable types can't hold null values [OK]

Common Mistakes:

• Thinking Kotlin allows null for Int by default
• Assuming semicolons are required
• Believing print syntax is wrong

5. How does Kotlin achieve both simplicity in source code and performance similar to Java primitives?

hard

A. By using compiler optimizations to convert Kotlin types to JVM primitives

B. By forcing developers to write Java code for primitives

C. By not supporting primitive types at all and using only objects

D. By interpreting Kotlin code at runtime without compilation

Solution

1. Step 1: Understand Kotlin's compilation process

   Kotlin source code uses simple types like Int but the compiler converts them to JVM primitives for speed.

2. Step 2: Recognize the benefit of this approach

   This hides complexity from developers while keeping performance high like Java primitives.

3. Final Answer:

   By using compiler optimizations to convert Kotlin types to JVM primitives -> Option A

4. Quick Check:

   Kotlin compiler converts types to primitives [OK]

Hint: Compiler converts Kotlin types to primitives for speed [OK]

Common Mistakes:

• Thinking Kotlin requires manual Java code for primitives
• Believing Kotlin only uses objects without optimization
• Assuming Kotlin is interpreted without compilation