Weird.scala

// Scala 2.11.6-2.11.8
object WeirdCompileError {
  import java.util
  import javax.servlet.http.HttpServletRequest


  // In HttpServletRequest: public Enumeration<String> getHeaderNames();
  // http://docs.oracle.com/javaee/7/api/javax/servlet/http/HttpServletRequest.html#getHeaderNames--
  
  // Error
  // [error]  found   : java.util.Enumeration[?0] where type ?0
  // [error]  required: java.util.Enumeration[String]
  // [error]   val headerRequest: util.Enumeration[String] = request.getHeaderNames()

  val request: HttpServletRequest = ???
  val headerRequest: util.Enumeration[String] = request.getHeaderNames()
  
  // Compiles
  val request2: HttpServletRequest = ???
  val headerRequest2: util.Enumeration[String] = request.getHeaderNames().asInstanceOf[util.Enumeration[String]]
}