Functions and lambdas in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function in Kotlin?

A function is a reusable block of code that performs a specific task. It can take inputs, called parameters, and can return a result.

beginner

How do you declare a simple function in Kotlin that adds two numbers?

fun add(a: Int, b: Int): Int { return a + b }

intermediate

What is a lambda expression in Kotlin?

A lambda is a small anonymous function that can be passed as a value. It is often used for short pieces of code like callbacks or operations on collections.

intermediate

How do you write a lambda that multiplies a number by 2?

val double = { x: Int -> x * 2 }

intermediate

What is the difference between a named function and a lambda in Kotlin?

A named function has a name and can be called anywhere by that name. A lambda is anonymous and usually used as a value passed to other functions.

How do you declare a function in Kotlin that returns no value?

A fun greet() { println("Hi") }

B fun greet(): Int { println("Hi") }

C fun greet() -> Unit { println("Hi") }

D function greet() { println("Hi") }

In Kotlin, a function that returns no value has return type Unit, which can be omitted. So fun greet() { ... } is correct.

What symbol separates parameters and the body in a lambda expression?

A :

B ->

C =

D =>

In Kotlin lambdas, the arrow -> separates the parameter list from the body.

Which of these is a valid lambda that takes no parameters and returns 5?

A { -> 5 }

B fun() = 5

C { x -> 5 }

D { 5 }

If a lambda has no parameters, you can omit the arrow and just write { 5 }.

How do you call a function named 'sum' with arguments 3 and 4?

A sum(3, 4)

B sum 3, 4

C call sum(3, 4)

D sum.call(3,4)

Functions in Kotlin are called by their name followed by parentheses with arguments inside.

What is the type of the lambda val square = { x: Int -> x * x }?

A Unit

B Int

C (Int) -> Int

D Function

The lambda takes an Int and returns an Int, so its type is (Int) -> Int.

Explain how to declare and use a simple function in Kotlin with parameters and a return value.

Think about how you tell the app to do something with inputs and give back a result.

Describe what a lambda expression is and give an example of when you might use one in an Android app.

Imagine you want to quickly tell a button what to do when clicked without writing a full function.