scala.EnumerationをJavaから使う場合

Enum.scala

/*
 * scalac Enum.scala
 */

/**
 * Define Signal Enumeration
 */
object Signal extends Enumeration {

  val Green  = Value        //=> Val(0, "Green")
  val Yellow = Value(2)     //=> Val(2, "Yellow")
  val Red    = Value("RED") //=> Val(3, "RED")

  // Alias for Java
  def valueOf(name: String) = withName(name)

  // Java-like methods addition (can't use implicitly from Java)
  implicit class JavaLikeValue(v: Value) {
    def name = v.toString
    def ordinal = v.id
  }
}

/**
 * Use Signal
 */
object ScalaMain extends App {

  // Iteration
  Signal.values.foreach { signal =>
    println(s"id: ${signal.id}, toString: ${signal}")
  }

  // Get singleton instance
  val g = Signal.Green
  val y = Signal(2)              // by id
  val r = Signal.withName("RED") // by name

  // Mapping function
  def toMessage = {
    import Signal._ // import for shortcut

    // pattern match (like switch-case in Java)
    (_: Value) match {
       case Green  => "Go ahead"
       case Yellow => "Be careful"
       case Red    => "Stop"
    }
  }
  println( toMessage(r) )

  // implicit conversion
  println( g.name )
  println( y.ordinal )
}

Main.java

/**
 * javac -cp scala-library.jar:. Main.java
 * java -cp scala-library.jar:. Main
 */
public class Main {
  public static void main(String[] args) {
    // Signal class
    System.out.println(Signal.class.toString());

    // Signal$ class (Signal.type @ Scala)
    System.out.println(Signal$.class.toString());

    // Signal singleton object
    Signal$ obj = Signal$.MODULE$;
    System.out.println(obj.toString());

    // Get enumeration instance
    System.out.println(Signal.Green().toString());
    System.out.println(Signal.apply(2).toString());
    System.out.println(Signal.withName("RED").toString());
    System.out.println(Signal.valueOf("RED").toString());

    // Instance Type (Inner class of singleton object class)
    Signal$.Value a = Signal.Yellow();
    System.out.println(a.id());

    // Use methods explicitly
    System.out.println(new Signal.JavaLikeValue(Signal.Green()).name());
  }
}