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The classification of basic types

In this lesson, we will learn about the classification and properties of the basic types provided by Kotlin. You may have already met some of them. The basic types can be separated into several groups according to meaning. Types from the same group can be operated in the same way, but have different sizes and, as a consequence, represent different ranges of values.

You do not need to learn all of this by heart because it is easy to find it in the documentation or simply Google it. Though, a common understanding of these concepts is important in job interviews and practice.

Numbers

Kotlin provides several types for integers and fractional numbers.

Integer numbers (0, 1, 2, ...) are represented by the following four types: Long, Int, Short, Byte (from the largest to the smallest). These types have different sizes and may represent different ranges of values. The range of an integer type is calculated as −(2n−1) to (2n−1)−1, where n is the number of bits. The range includes 0, which is the reason for subtracting 1 from the upper bound.

  • Byte size 8 bits (1 byte), range from -128 to 127
  • Short size 16 bits (2 bytes), range from -32768 to 32767
  • Int size 32 bits (4 bytes), range from −(231) to (231)−1
  • Long size 64 bits (8 bytes), range from −(263) to (263)−1

The sizes of types are always the same. They do not depend on the operating system or hardware and you cannot change them.

The most commonly used integer types are Int and Long. Always try to use Int if it is enough for your purposes. Otherwise, use Long.

val zero = 0 // Int
val one = 1  // Int
val oneMillion = 1_000_000  // Int

val twoMillion = 2_000_000L // Long, because it is tagged with L
val bigNumber = 1_000_000_000_000_000 // Long, Kotlin automatically choose it (Int is too small)
val ten: Long = 10 // Long, because the type is specified

val shortNumber: Short = 15 // Short, because the type is specified
val byteNumber: Byte = 15   // Byte, because the type is specified

Floating-point types represent numbers with fractional parts. Kotlin has two such types: Double (64 bits) and Float (32 bits). These types can store only a limited number of significant decimal digits (~6-7 for Float and ~14-16 for Double). As a rule, you will use the Double type in practice.

val pi = 3.1415  // Double
val e = 2.71828f // Float, because it is tagged with f
val fraction: Float = 1.51 // Float, because the type is specified

To display the maximum and minimum value of a numeric type (including Double and Float), you need to write the type name followed by a dot and then either MIN_VALUE or MAX_VALUE.

println(Int.MIN_VALUE)  // -2147483648
println(Int.MAX_VALUE)  // 2147483647
println(Long.MIN_VALUE) // -9223372036854775808
println(Long.MAX_VALUE) // 9223372036854775807

It is also possible to get the size of an integer type in bytes or bits (1 byte = 8 bits):

println(Int.SIZE_BYTES) // 4
println(Int.SIZE_BITS)  // 32

Characters

Kotlin has a type named Char to represent letters (uppercase and lowercase), digits, and other symbols. Each character is just a single letter enclosed in single quotes. This type has the same size as the Short type (2 bytes = 16 bits).

val lowerCaseLetter = 'a'
val upperCaseLetter = 'Q'
val number = '1'
val space = ' '
val dollar = '$'

Characters can represent symbols from many alphabets including hieroglyphs, as well as some special symbols that we will take a look at later.

Booleans

Kotlin provides a type called Boolean, which can store only two values: true and false. It represents only one bit of information, but its size is not precisely defined.

val enabled = true
val bugFound = false

We will often use this type in conditionals.

Strings

The String type represents a sequence of characters enclosed in double quotes. Actually, it is one of the most used types.

val creditCardNumber = "1234 5678 9012 3456"
val message = "Learn Kotlin instead of Java."

As a recap, note that the most commonly used of the types mentioned above are String, Int, Long, Boolean, Char, and Double. We will learn about other data types later. Remember that Long is the largest integer type. Knowing the sizes and ranges of integer types may help you get a job.