Updating JLabel with thread

Question

I'm trying to get a thread to run for a swing application on button click, but the value isn't updating. It supposed to grab the computer name I'm searching, but in order for the value to update I have to launch a new instance of the GUI. I created a thread, but for some reason it's not working. Any help is appreciated.

(t.start is at end of code block)

searchComputerButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
              Thread t = new Thread("my non EDT thread") {
                    public void run() {
                        //my work
                        testLabel.setText(CN);
                    }

                };

            String line;
            BufferedWriter bw = null;
            BufferedWriter writer = null;
            try {
                writer = new BufferedWriter(new FileWriter(tempFile));
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            // String lineToRemove = "OU=Workstations";

            String s = null;

            Process p = null;
            /*
             * try { // p = Runtime.getRuntime().exec(
             * "cmd /c start c:\\computerQuery.bat computerName"); } catch
             * (IOException e1) { // TODO Auto-generated catch block
             * e1.printStackTrace(); }
             */
            try {

                p = Runtime.getRuntime().exec("c:\\computerQuery.bat");

            } catch (IOException e1) {

                // TODO Auto-generated catch block

                e1.printStackTrace();

            }
            StringBuffer sbuffer = new StringBuffer();
            BufferedReader in = new BufferedReader(new InputStreamReader(p
                    .getInputStream()));

            try {

                while ((line = in.readLine()) != null) {

                    System.out.println(line);

                    // textArea.append(line);

                    String dn = "CN=FDCD111304,OU=Workstations,OU=SIM,OU=Accounts,DC=FL,DC=NET";
                    LdapName ldapName = new LdapName(dn);
                    String commonName = (String) ldapName.getRdn(
                            ldapName.size() - 1).getValue();

                }
                ComputerQuery.sendParam();

            } catch (IOException e1) {

                // TODO Auto-generated catch block

                e1.printStackTrace();

            } catch (InvalidNameException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            } finally

            {
                try {
                    fw.close();

                }

                catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }

            try {

                in.close();

            } catch (IOException e1) {

                // TODO Auto-generated catch block

                e1.printStackTrace();

            }

            ComputerQuery.sendParam();
            t.start();
        }
    });

UPDATE

private void threadStart() {
          SwingUtilities.invokeLater(new Runnable() {
            public void run() {

              testLabel.setText(CN);
            }
          });

And I put the method here

JButton searchComputerButton = new JButton("Search");
        searchComputerButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                threadStart();
                String line;

Answer 1

Be aware of the Swing Thread https://docs.oracle.com/javase/tutorial/uiswin/concurrency/

Have a look here: http://www.javamex.com/tutorials/threads/invokelater.shtml

You must enqueue your JLabel update method invocation using the Method SwingUtilities.invokeLater(???). Following example does it

Further more i think that is has something to do with the .batch file invocations. Have a look here: How do I run a batch file from my Java Application? Runnable task = new UpdateJob("Query: " + i); SwingUtilities.invokeLater(task);

---

To make it more understandable.

Swing manages all draw-Operations, within one Thread. It provides a queue. If you call a method from outside of that queue the behaviour is completely unpredictable.. NullPointer... RuntimeExc.... But if you call SwingUtilities.invokeLater(...) your method will be enqueued into the Swing-Queue and invoked as soon as possible!

UPDATE due to comment:

check your mainthread (GUI) check your threads. when a sub-thread (e.g a ActionListener) want to call JLabel::setText it has to use the method SwingUtils::InvokeLater("...");

That means invokeLater() has to be call within all threads which not directly belong to the main threads.

UPDATE due to Question

In my oppinion you current't code doesn't need SwingUtilities.invok.. at all. Did you change the Code assigned to you your question.