Data types and type inference in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a data type in Kotlin?

A data type defines the kind of value a variable can hold, like numbers, text, or true/false values.

beginner

What does val mean in Kotlin?

val declares a read-only variable, which means its value cannot change after it is set.

beginner

Explain type inference in Kotlin.

Type inference means Kotlin can guess the data type of a variable from the value you assign, so you don't always need to write the type explicitly.

beginner

What is the difference between Int and Double in Kotlin?

Int holds whole numbers without decimals, while Double holds numbers with decimals.

beginner

How do you explicitly declare a variable type in Kotlin?

You write the variable name, then a colon, then the type. For example: val age: Int = 30.

Which keyword declares a variable whose value cannot change in Kotlin?

A val

B var

C let

D const

val declares a read-only variable, while var allows changes.

What type will Kotlin infer for val name = "Anna"?

A String

B Int

C Boolean

D Double

Kotlin infers String because the value is text in quotes.

Which data type should you use for a number with decimals?

A Int

B Double

C String

D Boolean

Double holds decimal numbers.

How do you explicitly declare a variable of type Int?

A val number = 5 as Int

B val number = Int(5)

C val Int number = 5

D val number: Int = 5

The correct syntax is val number: Int = 5.

What happens if you try to change a val variable?

A It changes successfully

B It changes at runtime

C You get a compile error

D It changes only sometimes

val variables cannot be reassigned; the compiler will show an error.

Explain how Kotlin's type inference helps when declaring variables.

Think about how Kotlin figures out the type from the value you give.

Describe the difference between val and var in Kotlin.

Consider if the variable can be changed or not.