从其他类中的线程调用时不重新出现

Question

I am trying to make a simple artillery game and print a circle moving across the screen in an arc when a button is clicked.

On click i create a thread and calculate the location of the "projectile" and print out a circle at the calculate x and y locations.

When i execute the code from the one class it calls repaint and plots the trajectory of the "projectile" but when i set up a separate class to call it and print it out on the click of a button it does not call the repaint from the loop.

When i execute the class below by itself displays what i want.

import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Pong4 extends JPanel implements Runnable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    private ScreenLocation location;

    private boolean renderBulit = false;

    public static void main(String[] args)
    {
        Pong4 p = new Pong4();

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(p);
        frame.setSize(800, 600);
        frame.setVisible(true);

        Thread thread = new Thread(p);
        thread.start();
        try {
            thread.join();
        } catch (InterruptedException ex) {
            // TODO Auto-generated catch block
            ex.printStackTrace();
        }
    }

    public Pong4()
    {
    }

    public ScreenLocation updatePosition(ScreenLocation location, double xSpeed, double ySpeed, double time) 
    {   
        return new ScreenLocation((int)(location.getX() + xSpeed * time), (int)(location.getY() - ySpeed * time));
    }


    @Override
    public void run()
    {

        double time = 0;
        location = new ScreenLocation(100, 400);
        renderBulit = true;

        double xSpeed = 50;
        double ySpeed = 50;

        while (location.getX() >= 0 && 800 > location.getX() && 400 >= location.getY())
        {       
            repaint();

            System.out.println("test");

            try {
                Thread.sleep(15);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            time += 0.01;
            location = updatePosition(location, xSpeed, ySpeed, time);
            ySpeed = ySpeed - Constants.GRAVITY * time;
        }

        renderBulit = false;
        repaint();

    }

    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponents(g); 
        Graphics2D g2d = (Graphics2D)g;

        // Paint a gradient from top to bottom
        GradientPaint gp = new GradientPaint( 0, 0, Color.BLACK,
            0, getHeight( ), new Color(0, 0, 255).darker( ).darker() );

        g2d.setPaint( gp );
        g2d.fillRect( 0, 0, getWidth( ), getHeight( ) );

        if (renderBulit)
        {
            // draw circle (color already set to foreground)
            g.setColor(Color.red);
            g.fillOval(location.getX(), location.getY(), 4, 4);
            g.drawOval(location.getX(), location.getY(), 4, 4);


            //Image image = new ImageIcon("src/au/com/tankwarz/view/resources/images/BULIT0.GIF").getImage();
            //g.drawImage(image, location.getX(), location.getY(), this); 
        }
        g2d.dispose();       
    }

    public class ScreenLocation 
    {
        private int x;

        private int y;

        public ScreenLocation (int x, int y)
        {
            this.x = x;
            this.y = y;
        }

        public int getX() {
            return x;
        }

        public void setX(int x) {
            this.x = x;
        }

        public int getY() {
            return y;
        }

        public void setY(int y) {
            this.y = y;
        }


    }
}

But when i try the following it does not display.

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

import org.jdesktop.application.Application;

public class Pong3 extends JPanel{

    public static void main(String[] args)
    {

        new Pong3();
    }

    private static final long serialVersionUID = 2944576178447230562L;

    private JButton fireButton;
    private JPanel controlsPanel;

    private Pong4 pong;

    public Pong3() {
        super();
        initGUI();

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(this);
        frame.setSize(800, 600);
        frame.setVisible(true);
    }

    private void initGUI() {
        try {
            this.setPreferredSize(new java.awt.Dimension(800, 600));
            this.setSize(800, 600);
            this.setLayout(null);
            {
                pong = new Pong4();
                this.add(pong);
                pong.setLayout(null);
                pong.setBounds(0, 0, 800, 450);
            }           
            {
                controlsPanel = new JPanel();
                this.add(controlsPanel);
                GridBagLayout controlsPanelLayout = new GridBagLayout();
                controlsPanelLayout.rowWeights = new double[] {0.1, 0.1, 0.1, 0.1};
                controlsPanelLayout.rowHeights = new int[] {7, 7, 7, 7};
                controlsPanelLayout.columnWeights = new double[] {0.1, 0.1, 0.1, 0.1};
                controlsPanelLayout.columnWidths = new int[] {7, 7, 7, 7};
                controlsPanel.setLayout(controlsPanelLayout);
                controlsPanel.setBounds(0, 450, 800, 110);
                controlsPanel.setName("controlsPanel");

                {
                    fireButton = new JButton();
                    controlsPanel.add(fireButton, new GridBagConstraints(3, 1, 1, 1, 0.0, 0.0, GridBagConstraints.CENTER, GridBagConstraints.NONE, new Insets(0, 0, 0, 0), 0, 0));
                    fireButton.setName("fireButton");
                    fireButton.setText("Fire");
                    fireButton.setPreferredSize(new java.awt.Dimension(104, 51));
                    fireButton.addActionListener(new ActionListener() {

                        @Override
                        public void actionPerformed(ActionEvent e) {            
                            Thread thread = new Thread(pong);
                            thread.start();
                            try {
                                thread.join();
                            } catch (InterruptedException ex) {
                                // TODO Auto-generated catch block
                                ex.printStackTrace();
                            }


                        }
                    });
                }
            }
            Application.getInstance().getContext().getResourceMap(getClass()).injectComponents(this);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

Would appreciate any help as to why this acts this way.

Answer 1

Your thread.join() undoes all the benefits of trying to use a background thread by tying the "background" thread with the current thread, and thus you should not be doing this. The only reason things seem to work in the first code is due to your code initially running not in the event dispatch thread, and so your join() call joins the thread to the main thread, not the EDT, and so does not freeze the EDT. Either way, the join() is out and out wrong.

A much better solution I think is to use a Swing Timer. This will eliminate the need for explicit use of background threads.

As an aside: avoid using null layouts if you want to create GUI's with powerful, flexible, and good looking layouts.