Lambda syntax and declaration in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin lambda expression?

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

Kotlin

val multiplyByTwo = { x: Int -> x * 2 }
println(multiplyByTwo(5))

A 10

B 25

C 5

D Compilation error

💡 Hint

Remember the lambda takes an integer and multiplies it by 2.

The lambda takes an integer x and returns x multiplied by 2. So multiplyByTwo(5) returns 10.

❓ Predict Output

intermediate

What does this Kotlin lambda return?

What is the output of this Kotlin code?

Kotlin

val greet: (String) -> String = { name -> "Hello, $name!" }
println(greet("Anna"))

A Hello, name!

B Hello, Anna!

C greet

D Compilation error

💡 Hint

The lambda uses string interpolation with the parameter name.

The lambda takes a string and returns "Hello, " plus the name plus "!". So it prints "Hello, Anna!".

❓ Predict Output

advanced

What is the output of this Kotlin lambda with implicit it?

What will this Kotlin code print?

Kotlin

val square: (Int) -> Int = { it * it }
println(square(4))

A 16

B 4

C Itself (function reference)

D Compilation error

💡 Hint

When a lambda has one parameter, you can use 'it' to refer to it.

The lambda squares the input number. 4 squared is 16, so it prints 16.

❓ Predict Output

advanced

What is the output of this Kotlin lambda with multiple parameters?

What will this Kotlin code print?

Kotlin

val sum: (Int, Int) -> Int = { a, b -> a + b }
println(sum(3, 7))

A 37

B 3

C Compilation error

D 10

💡 Hint

The lambda adds two integers a and b.

The lambda adds 3 and 7, resulting in 10, which is printed.

🧠 Conceptual

expert

Which Kotlin lambda declaration correctly defines a lambda that returns the length of a string?

Choose the correct Kotlin lambda declaration that takes a String and returns its length as an Int.

A val lengthLambda: (String) -> String = { s -> s.length }

B val lengthLambda = { s: String -> s.length }

C val lengthLambda: (String) -> Int = { s -> s.length }

D val lengthLambda: (Int) -> Int = { s -> s.length }

💡 Hint

Check the lambda parameter type and return type carefully.

Option C correctly declares a lambda taking a String and returning an Int (the length). Option C misses explicit type but is valid Kotlin, but since the question asks for declaration with type, A is best. Option C returns String but length is Int, so wrong return type. Option C takes Int but tries to get length, which is invalid.