JProgressBar - Won't work in the class that I am calling it in

Question

I'm making a project and need a progress bar. I've got the class with the Timer and it runs fine when I include a main; but when I try to call it in the mainGUI method, it's all black until it hits 100% then appears.

package microproject.resources;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class Timer extends JFrame {

    JProgressBar current;
    JTextArea out;
    JButton find;
    Thread runner;
    int num = 0;
    int length = 0;

    public Timer() {
        setTitle("Progress");
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        length = Integer.parseInt(JOptionPane.showInputDialog(null, "How many seconds:"));

        JPanel p = new JPanel(new GridLayout(1,1));
        p.setPreferredSize(new Dimension(300,65));
        current = new JProgressBar(0, length);
        current.setPreferredSize(new Dimension(250,50));
        current.setValue(0);
        current.setStringPainted(true);
        p.add(current);
        setVisible(true);
        setContentPane(p);
        pack();
        setVisible(true);
        iterate();
    }

    public void iterate() {
        while(num < length +1) {
            current.setValue(num);
            try {
                Thread.sleep(1000);
            } catch(InterruptedException e) {}
            num += 1;
        }

    }

    public static void main(String[] args) {
        Timer f = new Timer();
    }
}

This is the code for the Timer Class ^

package microproject.resources;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class GUIMain extends JFrame {

    public static void main(String []args){            
        GuiFrame();        
    }    

    public static void GuiFrame(){
        JFrame frame = new JFrame("Casino Royal3");
        frame.setSize(811,577);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);

        frame.setLayout(new GridLayout(2,1));
        frame.setResizable(false);
        JPanel PNorth = new JPanel(new FlowLayout(FlowLayout.LEFT,0,0));
        JPanel PSouth = new JPanel(new BorderLayout());


        //Creating Image for Casino Button
        ImageIcon img1 = new ImageIcon("src\\Casino.jpg");
        final JButton btn1 = new JButton(img1);
        btn1.setPreferredSize(new Dimension(550,274));
        btn1.setMargin(new Insets(0,0,0,0));
        PNorth.add(btn1, BorderLayout.EAST);
        btn1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                btn1.setIcon(new ImageIcon("src\\Casino2.jpg"));
            }
        });

        //Creating Image for Sheridan Label
        ImageIcon img2 = new ImageIcon("src\\SHERIDAN_LOGO.jpg");
        JButton btn2 = new JButton(img2);
        btn2.setMargin(new Insets(0,0,0,0));
        PNorth.add(btn2);
        btn2.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                ImageIcon instruc = new ImageIcon("src\\Instructions.jpg");
                JLabel instructions = new JLabel(instruc);
                JOptionPane.showConfirmDialog(null, instructions, "instructions", JOptionPane.DEFAULT_OPTION, JOptionPane.PLAIN_MESSAGE);
            }
        });

        JPanel timmus = new JPanel(new FlowLayout(FlowLayout.LEFT,0,0));
        timmus.setPreferredSize(new Dimension(166, 273));
        timmus.setBackground(Color.BLUE);

        ImageIcon time = new ImageIcon("src\\Timer.jpg");
        JButton timer = new JButton(time);
        timer.setMargin(new Insets(0,0,0,0));
        timer.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                Timer f = new Timer();
            }
        });
        timmus.add(timer);

        ImageIcon mus = new ImageIcon("src\\music.jpg");
        JButton music = new JButton(mus);
        music.setMargin(new Insets(0,0,0,0));
        timmus.add(music);

        JPanel games = new JPanel(new FlowLayout(FlowLayout.LEFT,0,0));
        games.setPreferredSize(new Dimension(500,279));
        games.setBackground(Color.BLUE);

        ImageIcon calculator = new ImageIcon("src\\Calculator.jpg");
        JButton calc = new JButton(calculator);
        calc.setMargin(new Insets(0,0,0,0));
        calc.setPreferredSize(new Dimension(166,273));
        games.add(calc);
        calc.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                Calculator c1 = new Calculator();
            }
        });

        ImageIcon g1 = new ImageIcon("src\\250Hangman.jpg");
        JButton game1 = new JButton(g1);
        //game1.setBackground(Color.WHITE);
        game1.setMargin(new Insets(0,0,0,0));
        game1.setPreferredSize(new Dimension(166,273));
        games.add(game1);
        game1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                Hangman h1 = new Hangman();
            }
        });


        ImageIcon g2 = new ImageIcon("src\\Minesweeper.jpg");
        JButton game2 = new JButton(g2);
    //    game2.setBackground(Color.WHITE);
        game2.setMargin(new Insets(0,0,0,0));    
        game2.setPreferredSize(new Dimension(166,273));
        games.add(game2);

        PSouth.add(timmus, BorderLayout.CENTER);
        PSouth.add(games, BorderLayout.EAST);

        frame.add(PNorth, BorderLayout.NORTH);
        frame.add(PSouth, BorderLayout.SOUTH);

        frame.setVisible(true);
        frame.pack();
    }
}

That's the entire program, the Timer ActionListener is called "timer"

Thanks in advance

Answer 1

Welcome to the wonderful world of blocked Event Dispatching Thread (and violation of the initial thread)

Basically, Swing is a single threaded environment, all updates and modifications to the UI are expected to be executed within the context of the Event Dispatching Thread (AKA EDT).

The EDT is responsible for, amongst other things, processing repaint requests. If, for some reason, you block this thread (for example, using a long running loop or blocking IO), it will prevent the EDT from processing new paint requests, making it appear as if your program has hung...because essentially it has.

The reason you might see a difference between running Timer directly and using it in your GUI is because when the application is started, it will be running within, what is commonly known as, the "main" thread.

When you first create a top level Swing container, the EDT is started (which is a separate thread), meaning that the UI will appear in it's own thread, but the application will continue running in the "main" thread, allowing your iterate method to run independently of the EDT.

However, when you try and run it from within your GUI, it's all running within the context of the EDT, causing it to be blocked.

Start by taking a look at

• Concurrency in Swing
• Initial Threads

To fix the problem, based on your example code, I would suggest using a SwingWorker. This will allow you to run your "long running task" in a background thread, but provides a number of methods that allow you to resync your updates back to the EDT. This is very important, as you should never attempt to update the UI or change it's state from any thread other then the EDT.

Take a look at Worker Threads and SwingWorker for more details

And if required, some examples...

• JProgressBar not updating
• JProgressBar too fast
• JProgressBar won't update
• Progress Bar Java