src/Tools/jEdit/src/document_view.scala

 
 import isabelle._
 
 import scala.actors.Actor._
 
+import java.lang.System
 import java.awt.{BorderLayout, Graphics, Color, Dimension, Graphics2D, Point}
 import java.awt.event.{MouseAdapter, MouseMotionAdapter, MouseEvent,
   FocusAdapter, FocusEvent, WindowEvent, WindowAdapter}
 import javax.swing.{JPanel, ToolTipManager, Popup, PopupFactory, SwingUtilities, BorderFactory}
 import javax.swing.event.{CaretListener, CaretEvent}