Swing components freezing until one component completes its job

Question

I have created a simple JAVA Swing program that has a JTextArea, three JTextFields and one JButton. What this application does is when the user clicks the button it updates the JTextArea with a text line, the text line inserted into the JTextArea is prepared in a for loop and number of repeat times is given in a JTextField.

My problem is when I click the start JButton all the components of the application are freeze, I can't even close the window until the for loop completes it's job. How can I separate this JTextField updating work from other tasks in the form?

Answer 1

You are probably doing the work on the Event Dispatch Thread (the same thread as the GUI rendering is done). Use SwingWorker it will do the work in another thread instead.

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Example

Code below produces this screenshot:

Example worker:

static class MyWorker extends SwingWorker<String, String> {

    private final JTextArea area;

    MyWorker(JTextArea area) {
        this.area = area;
    }

    @Override
    public String doInBackground() {
        for (int i = 0; i < 100; i++) {
            try { Thread.sleep(10); } catch (InterruptedException e) {}
            publish("Processing... " + i);
        }
        return "Done";
    }
    @Override
    protected void process(List<String> chunks) {
        for (String c : chunks) area.insert(c + "\n", 0);
    }
    @Override
    protected void done() {
        try {
            area.insert(get() + "\n", 0);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Example main:

public static void main(String[] args) throws Exception {

    final JTextArea area = new JTextArea();

    JFrame frame = new JFrame("Test");

    frame.add(new JButton(new AbstractAction("Execute") {            
        @Override
        public void actionPerformed(ActionEvent e) {
            new MyWorker(area).execute();
        }
    }), BorderLayout.NORTH);

    frame.add(area, BorderLayout.CENTER);

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 300);
    frame.setVisible(true);
}