Kotlin learning: Kotlin enumeration class

Kotlin Enumeration

The most basic usage of an enumeration class is to implement a type-safe enumeration.

Enumeration constants are separated by commas, and each enumeration constant is an object

enum class Color{
    RED,BLACK,BLUE,GREEN,WHITE
}

Enumeration initialization

Each enumeration is an instance of the enumeration class, they can be initialized

enum class Color(val rgb: Int) {
    RED(0xFF0000),
    GREEN(0x00FF00),
    BLUE(0x0000FF)
}

The default name is the enumerated character name, and the value starts from 0. If you need to specify a value, you can use its constructor

enum class Shape(value:Int){
    ovel(100),
    rectangle(200)
}

Enumerations also support to declare their own anonymous classes and corresponding methods, as well as to override the methods of the base class. Such as

enum class ProtocolState {
    WAITING {
        override fun signal() = TALKING
    },

    TALKING {
        override fun signal() = WAITING
    };

    abstract fun signal(): ProtocolState
}

If the enumeration class defines any members, use a semicolon to separate the enumeration constant definition in the member definition

Use enum constants

The enumeration class in Kotlin has a synthetic method that allows it to traverse the defined enumeration constant and obtain the enumeration constant by its name

EnumClass.valueOf(value: String): EnumClass  // 转换指定 name 为枚举值，若未匹配成功，会抛出IllegalArgumentException
EnumClass.values(): Array<EnumClass>        // 以数组的形式，返回枚举值

Get enumeration related information:

val name: String //获取枚举名称
val ordinal: Int //获取枚举值在所有枚举数组中定义的顺序

Instance

enum class Color{
    RED,BLACK,BLUE,GREEN,WHITE
}

fun main(args: Array<String>) {
    var color:Color=Color.BLUE

    println(Color.values())
    println(Color.valueOf("RED"))
    println(color.name)
    println(color.ordinal)

}

Since Kotlin 1.1, you can use the  enumValues<T>() and  enumValueOf<T>() function to access the constants in the enumeration class in a generic way

enum class RGB { RED, GREEN, BLUE }

inline fun <reified T : Enum<T>> printAllValues() {
    print(enumValues<T>().joinToString { it.name })
}



fun main(args: Array<String>) {
    printAllValues<RGB>() // 输出 RED, GREEN, BLUE
}