Enumerations are usually used to define constants of known quantities, such as months, weeks, seasons, etc. People who have used java know that the keyword for defining enumerations is enum, which is different from java in scala. Let's see a complete Example definition:
object EnumTest {
/***
* Define an enumeration for a week
*/
object WeekDay extends Enumeration{
type WeekDay = Value //Declare the type of variables exposed by the enumeration
val Mon = Value("1")
val Tue = Value("2")
val Wed = Value("3")
val Thu = Value("4")
val Fri = Value("5")
val Sat = Value("6")
val Sun = Value("7")
def checkExists(day:String) = this.values.exists(_.toString==day) //Check whether this enumeration value exists
def isWorkingDay(day:WeekDay) = ! ( day==Sat || day == Sun) //Determine whether it is a working day
def showAll = this.values.foreach(println) // print all enumeration values
}
def main(args: Array[String]): Unit = {
println(WeekDay.checkExists("8"))//Check if it exists
println(WeekDay.Sun==WeekDay.withName("7"))//Correct usage
println(WeekDay.Sun=="7")//Wrong usage
WeekDay.showAll //Print all enumeration values
println(WeekDay.isWorkingDay(WeekDay.Sun)) //Whether it is a working day
}
}
The above example basically covers all the common methods of enumeration. To define enumeration, we inherit the Enumeration abstract class, and then assign the value of each enumeration through the internal object Value. In addition, it also defines several tool methods, such as Determine whether there is an enumeration, whether it is a working day, and print all enumeration values, which can be accessed directly through Object when used.
You can also use enumeration values for pattern matching:
val weekDay=WeekDay.Sun
weekDay match {
case WeekDay.Mon=> println("Monday")
case WeekDay.Tue=> println("Tuesday")
case WeekDay.Wed=> println("Wednesday")
case WeekDay.Thu=> println("Thursday")
case WeekDay.Fri=> println("Friday")
case WeekDay.Sat=> println("Saturday")
case WeekDay.Sun=> println("Sunday")
}
//Sunday
The above is basically the most common enumeration method in Scala. Of course, this common enumeration has some disadvantages, such as the pattern matching above. If I only write 3 enumeration values, it can still pass at compile time, but in An error will be reported when running. In the end, this method cannot enumerate an object, but a simple type. If the value to be enumerated is itself a Bean, then another method is required, which will not be expanded here. Interested Friends can refer to the following link:
http://pedrorijo.com/blog/scala-enums/
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