When the Debug Panel is visible, it is normally attached to DrJava's main frame and displayed just above the bottom panes, and below the editor pane. To conserve screen space or make better use of dual monitors, the Debug Panel can also be detached.
To do this, click on the "Detach Debugger" menu item in the "Debug" menu and make sure that a checkmark appears next to "Detach Debugger". All debugger controls are now displayed in a separate window called "Debugger". To re-attach the "Debugger" window to DrJava's main frame, remove the checkmark next to "Detach Debugger" or close the "Debugger" window.