val classes = (new ClassExtractor ).visit(ctx).map(c => new OMPClass(c, parser))
//----------------------
class ClassExtractor extends Java8BaseVisitor[List[Java8Parser.ClassDeclarationContext]] {
    type CDC = Java8Parser.ClassDeclarationContext
    override def visitClassDeclaration(classCtx: CDC) = List[CDC](classCtx)
    override def defaultResult() = List[CDC]()
    override def aggregateResult(a: List[CDC], b: List[CDC]) = a ::: b
}