void (FrameDiffTool.DiffViewer viewer) { ThreadingAssertions.assertEventDispatchThread(); if (viewer instanceof UnifiedDiffViewer) { myCaretTracker = new UnifiedCaretTracker((UnifiedDiffViewer)viewer); } else if (viewer instanceof SimpleDiffViewer) { myCaretTracker = new SimpleCaretTracker((SimpleDiffViewer)viewer); } else { myCaretTracker = null; } }