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Kotlin Crash Course for Programmers

Basic Data Types

Explore the fundamental data types in Kotlin including integers, floats, characters, and booleans. Understand Kotlin's static typing and how its types correspond to Java bytecode. This lesson helps you safely manage data values and prepares you for Kotlin's type inference and null safety concepts.

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Kotlin is a statically typed language, meaning that the data type of every expression is known at compile time.

Integers

There are four basic data types to store integer numbers of different sizes in Kotlin:

Kotlin
val byte: Byte = 127
val short: Short = 32767
val int: Int = 2147483647
val long: Long = 9223372036854775807

Note: The values assigned to each variable above are the largest allowed for the corresponding data type. This gives you an indication of their magnitude.

If you increase the assigned values even by one, the Kotlin compiler will complain because an overflow would occur at runtime (try it!).

Floating Point Numbers

Additionally, Kotlin has Float and Double to store floating point numbers up to different precision and sizes:

Kotlin
val float: Float = 3.4028235e38f

val double: Double = 1.7976931348623157e308

Here again, the assigned values are the maximum allowed for the corresponding type.

Two things to note:

  • The e in both values denotes exponentiation, for instance 1e3 == 1*10^3 == 1000.
  • In order to denote a Float value, you have to add the f suffix. Otherwise, Kotlin infers Double as the type of the number.

Text

Kotlin uses the Char type for single characters and String for arbitrary sequences of characters:

Kotlin
val character: Char = '#'
val text: String = "Learning about Kotlin's data types"

Single characters are denoted using single quotes '', whereas basic strings use double quotes "".

However, you can also use multiline strings by wrapping your string into three double quotes: """<multiline string here>""".

Booleans

Finally, Kotlin uses Boolean to store either true or false:

Kotlin
val yes: Boolean = true
val no: Boolean = false

These two are the only valid values for the Boolean type.

Note: Type Mapping to Java

Since Kotlin transpiles to Java bytecode (if you’re using it on the JVM), it’s important to explore how language concepts translate to Java.

In contrast to Java, Kotlin has no primitive types. All types discussed in this lesson are objects at runtime. However, they do transpile to Java’s primitive types in Java bytecode:

Kotlin Type Type in Java Bytecode
Byte byte
Short short
Int int
Long long
Float float
Double double
Char char
Boolean boolean

The mapping is quite trivial, but note that this mapping only works because Kotlin’s types cannot be null by default, just like Java’s primitive types cannot hold null. Kotlin’s approach to null safety is explained in detail later in the course.

Quiz

Data Types in Kotlin

1.

Which of these are valid data types to hold integers in Kotlin?

A.

Byte, Short, Int, Long

B.

Short, Int, Long, Boolean

C.

Byte, Int, Float, Long

1 / 3

Exercise

Create a variable favoriteMovie that stores the title of your favorite movie and a variable rating that contains your rating for it. Ratings range from 0.5 to 5.0 in increments of 0.5.

Problem
Solution
// Add your variables below

Summary

Here’s what you should take away from this lesson:

  • Kotlin has Byte, Short, Int, and Long as basic types for integer numbers.
  • Kotlin uses Float and Double for floating point numbers. A Float is denoted with a trailing f, as in 17f.
  • Kotlin has Char to store single characters and String to store strings of text.
  • Kotlin’s basic types map to Java’s primitive types when targeting the JVM (and String maps to String).

In the following lesson, you’ll understand how and when the Kotlin compiler can infer the types used in your code.