src/Tools/jEdit/src/monitor_dockable.scala

   /* chart data -- owned by GUI thread */
 
   private var statistics = Queue.empty[Properties.T]
   private var statistics_length = 0
 
-  private def add_statistics(stats: Properties.T)
+  private def add_statistics(stats: Properties.T): Unit =
   {
     statistics = statistics.enqueue(stats)
     statistics_length += 1
     limit_data.text match {
       case Value.Int(limit) =>

           statistics_length -= 1
         }
       case _ =>
     }
   }
-  private def clear_statistics()
+  private def clear_statistics(): Unit =
   {
     statistics = Queue.empty
     statistics_length = 0
   }
 

       stats =>
         add_statistics(stats.props)
         update_delay.invoke()
     }
 
-  override def init()
+  override def init(): Unit =
   {
     PIDE.session.runtime_statistics += main
   }
 
-  override def exit()
+  override def exit(): Unit =
   {
     PIDE.session.runtime_statistics -= main
   }
 }