What is an enumeration (enum) in Kotlin ?

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What is an enumeration (enum) in Kotlin ?

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What is an enumeration (enum) in Kotlin ?

last updated: 2 May 2024

Enumerations are a set of constants.
Declared with the word enum.

Example 1. values as Int

enum class BookType (val myValue: Int)
{
     Unknown (10),
     Fantasy (15),
     History (27),
     Child (28),
}

Full example:

Kotlin

enum class BookType (val myValue: Int)
{
     Unknown (10),
     Fantasy (15),
     History (27),
     Child (28),
}

fun main() {

     val myType1 = BookType.History

     println(myType1.myValue) // On the screen we will see 27
     println(myType1.name) // On the screen we will see History
}

Example 2. values as String

enum class BookType (val myValue: String)
{
     Unknown ("I don't know"),
     Fantasy ("It is very good to read fantasy books"),
     History ("I like read history books"),
     Child ("Lets see what child books I have"),
}

Full example:

Kotlin

enum class BookType (val myValue: String)
{
     Unknown ("I don't know"),
     Fantasy ("It is very good to read fantasy books"),
     History ("I like read history books"),
     Child ("Lets see what child books I have"),
}

fun main() {

     val myType1 = BookType.History

     println(myType1.myValue) // On the screen we will see I like read history books
     println(myType1.name) // On the screen we will see History
}

Writing a program

Step 1. Creating a new project

Create a new simple console project on Kotlin in IntelliJ IDEA ...

Step 2. Let's change the code in the file Main.kt

Kotlin

enum class BookType (val myValue: Int)
{
     Unknown (10),
     Fantasy (15),
     History (27),
     Child (28),
}

fun main() {

     val myType1 = BookType.History

     println(myType1.myValue)
     println(myType1.name)
}

Step 3. Launching the project

See the result at the bottom of the screen

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What is the difference between String and StringBuilder ?

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How do I find enum by value in Kotlin ?

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Объявления

Объявления

• What is Kotlin?

• Why is IntelliJ IDEA the most popular development environment for Kotlin?

• Download and install IntelliJ IDEA to explore Kotlin

• Create a new project in IntelliJ IDEA for study Kotlin

Int, Float, Boolean, Char ...

• Integer numbers in Kotlin are: Byte, UByte, Short, UShort, Int, UInt, Long, ULong

• Decimal numbers in Kotlin are: Float, Double

• A flag with values of true or false in Kotlin is: Boolean

• The symbol in Kotlin is: Char

• Convert number to text in Kotlin | Int → String

String

• The string, the text in Kotlin is: String

• Interpolate strings in Kotlin. Example: val address:String = "${street}, ${country}"

• What is the difference between String and StringBuilder ?

Enum

• What is an enumeration (enum) in Kotlin ?

• How do I find enum by value in Kotlin ?

Class

• What is class in Kotlin? Example: class MyBook { ... }

• lateinit is a late initialization for the class field | Kotlin

• class that inherits from interface in Kotlin | Example: class MyBook : IBook { ...}

• Unnamed class that inherits from interface in Kotlin | Example: val book1 = object : IBook { ...}

• Generic, template class in Kotlin | Example: class MyBook<T> { ... }

Collections and Arrays

• Create collections list, set, map and an array array in Kotlin

null

• null value, use the symbol ? and ?. and !! and ?: and !!. and ?. in Kotlin

Lambda function

• Lambda function in Kotlin. Example 1: var myFunc1 : (a:Int, b:Int) -> Int = { p1, p2 -> p1 + p2 };

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