title: How to fix "(java:22494): Gdk-WARNING..."
body: <p>I am writing a javafx program and I need the panel to update at a constant rate. Right now it is set to update every second. But I got this error, which is usually (but not always) followed by a glitch in the panel when the whole scene becomes distorted (it like mirrors in on itself in a weird choppy x pattern. hard to explain). </p>
  
  <p>Full error: (java:22494): Gdk-WARNING **: 18:38:59.118: XSetErrorHandler() called with a GDK error trap pushed. Don't do that.</p>
  
  <p>This is the code I have for the timer:</p>
  
  <pre><code>Timer timer = new Timer();
          timer.scheduleAtFixedRate(new TimerTask() {
              @Override
              public void run()  {
                  SwingUtilities.invokeLater(new Runnable() {
                      @Override
                      public void run() {
                          try {
                              String x = txtDisplay.getText();
                              txtDisplay.setText(x.substring(1, x.length()) + x.substring(0, 1));
                          } catch (NullPointerException e) {
                              System.out.println("Error.");
                          }
                      }
                  });
              }
          }, 0, 500);
  </code></pre>
  
  <p>I think the issue is with the above block, like maybe I am breaking some fundamental swing rule. My other idea is that it has something with two methods editing the same text area at the same time, because I have other methods setting the text area's text. </p>
  
  <p>I would be happy with either a solution to the error or a better way of executing the above method. Just needs to run every second without crashing.</p>
  
  <p>Thanks.</p>
  
  <p>EDIT: A new developement, I am now consistently getting a "Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException" but the stacktrace does not reference any locations that are in my code. </p>