Bei mir gibt es eine Exception:

Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException
at sun.font.FontDesignMetrics$MetricsKey.init(FontDesignMetrics.java:217)
at sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:286)
at sun.swing.SwingUtilities2.getFontMetrics(SwingUtilities2.java:1012)
at javax.swing.JComponent.getFontMetrics(JComponent.java:1624)
at javax.swing.text.WrappedPlainView.updateMetrics(WrappedPlainView.java:318)
at javax.swing.text.WrappedPlainView.setSize(WrappedPlainView.java:381)
at javax.swing.plaf.basic.BasicTextUI$RootView.setSize(BasicTextUI.java:1714)
at javax.swing.plaf.basic.BasicTextUI.modelToView(BasicTextUI.java:1046)
at javax.swing.text.DefaultCaret.repaintNewCaret(DefaultCaret.java:1307)
at javax.swing.text.DefaultCaret$1.run(DefaultCaret.java:1286)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:701)
at java.awt.EventQueue.access$000(EventQueue.java:102)
at java.awt.EventQueue$3.run(EventQueue.java:662)
at java.awt.EventQueue$3.run(EventQueue.java:660)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:671)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

Zur Lösung muß die Zeile

textArea.setFont(UIManager.getFont("ToolTip"));

durch

textArea.setFont(UIManager.getFont("ToolTip.font"));

ersetzt werden.