How to append text to a JTextArea?

Can't append text to a JTextArea from another class

• Found a similar topic on here but the solutions provided didn't work (or I'm just not seeing it). Here's my code reduced to the minimum: Here's the class I want to call the print method from: { HumanInterface gui = new HumanInterface(); gui.init(); gui.printToArea("from Main Class"); } and here's the HumanInterface class which extends JFrame { JTextArea area = createArea(); public void init() throws InvocationTargetException, InterruptedException { HumanInterface gst = new HumanInterface(); gst.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); gst.pack(); gst.setVisible(true); printToArea("print from HumanInterface class"); } public HumanInterface() throws InvocationTargetException, InterruptedException { Container container = getContentPane(); container.setLayout(new GridLayout(2, 3)); container.add(new JScrollPane(area)); } public void printToArea(String string) { try { updateArea(area, string); } catch (InvocationTargetException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } private JTextArea createArea() { final JTextArea area; area = new JTextArea(); area.setBackground(Color.GRAY); return area; } private void updateTextArea(final JTextArea textArea, final String string) throws InvocationTargetException, InterruptedException { SwingUtilities.invokeAndWait(new Runnable() { @Override public void run() { textArea.append(string); } }); } When I call printToArea(...) from anywhere else than from within the HumanInterface class, it doesn't work. What am I missing?

• Answer:

  The GUI you see is not the GUI you "want" to see, it's a second ;-) In your init() function you create a second HumanInterface: HumanInterface gst = new HumanInterface(); gst.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); gst.pack(); gst.setVisible(true); I think you probably want that (not tested): this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.pack(); this.setVisible(true);