SwingWorker example

import java.awt.BorderLayout;
import java.awt.event.KeyEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import javax.swing.*;

@SuppressWarnings("serial")
public class Example2 extends JPanel {
    private JTextArea textArea = new JTextArea(20, 50);
    private Task2 task2 = null;
    private JButton doItBtn = new JButton("Do it!");

    public Example2() {
        textArea.setFocusable(false);
        JScrollPane scrollPane = new JScrollPane(textArea);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        doItBtn.setMnemonic(KeyEvent.VK_D);
        doItBtn.addActionListener(e -> startTask());
        JPanel btnPanel = new JPanel();
        btnPanel.add(doItBtn);

        setLayout(new BorderLayout());
        add(scrollPane);
        add(btnPanel, BorderLayout.PAGE_END);
    }

    private void startTask() {
        doItBtn.setEnabled(false); // disable button
        task2 = new Task2();
        final MyWorker worker = new MyWorker(task2);
        worker.addPropertyChangeListener(pcsEvent -> {
            if (pcsEvent.getNewValue() == SwingWorker.StateValue.DONE) {
                doItBtn.setEnabled(true);

                try {
                    @SuppressWarnings("unused")
                    int result = worker.get();
                } catch (InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                    // TODO: show a JOptionPane error message if problem here
                }
            }
        });
        worker.execute();
    }

    class MyWorker extends SwingWorker<Integer, String> {

        private Task2 task2;

        public MyWorker(Task2 task2) {
            this.task2 = task2;
        }

        @Override
        protected Integer doInBackground() throws Exception {
            task2.addPropertyChangeListener(pcsEvent -> stateEvent(pcsEvent));
            int result = task2.doTask();
            return result;
        }

        private void stateEvent(PropertyChangeEvent event) {
            if (Task2.STATE.equals(event.getPropertyName())) {
                publish((String) event.getNewValue());
            }
        }

        @Override
        protected void process(List<String> chunks) {
            for (String chunk : chunks) {
                textArea.append(chunk + "\n");
            }
        }

    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            Example2 example = new Example2();

            JFrame frame = new JFrame("GUI");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(example);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }

}


class Task2 {
    public static final String STATE = "state";
    private PropertyChangeSupport pcs = new PropertyChangeSupport(this);
    private String state;

    public String getState() {
        return state;
    }

    public void setState(String state) {
        String oldValue = this.state;
        String newValue = state;
        this.state = state;

        pcs.firePropertyChange(STATE, oldValue, newValue);
    }

    public void addPropertyChangeListener(PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(listener);
    }

    public void removePropertyChangeListener(PropertyChangeListener listener) {
        pcs.removePropertyChangeListener(listener);
    }

    public int doTask() throws InterruptedException {
        //this method carrys out a background task an updates progress string throughout
        setState("Starting");
        System.out.println(getState());
        TimeUnit.SECONDS.sleep(2L);
        setState("hitting the flux capacitor");
        System.out.println(getState());
        TimeUnit.SECONDS.sleep(2L);
        setState("servicing Mr. Fusion");
        System.out.println(getState());
        TimeUnit.SECONDS.sleep(2L);
        setState("tuning Time circuits");
        System.out.println(getState());
        TimeUnit.SECONDS.sleep(2L);
        setState("cleaning Plutonium chamber");
        System.out.println(getState());
        TimeUnit.SECONDS.sleep(2L);
        setState("configuring Roentgen meter");
        System.out.println(getState());
        TimeUnit.SECONDS.sleep(2L);
        setState("finished");
        System.out.println(getState());

        return 0;
    }

}