Filling bar (progress bar) JApplet paint() Thread()

Question

Vertical bars should be filling to the height of the applet. When the top is reached, a new bar should start filling next to the previous. Problem: When the new bar starts filling the previous paint() /bar is cleared

img how it is: http://bayimg.com/DAEoeaagm

img how it should be: http://bayimg.com/dAeOgAaGm

the code:

import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JApplet;


public class fillingbar extends JApplet implements Runnable{

    int shifting=0,filling=0;
    public void init()
    {
        Thread t= new Thread(this);
        t.start();
        setSize(400,250);
    }

    public void paint(Graphics g)
    {
        super.paint(g);

            g.setColor(Color.GREEN);
            g.fillRect(shifting,getHeight()-filling,20,filling);

            g.setColor(Color.BLACK);
            g.drawRect(shifting, getHeight()-filling, 20, filling);
    }

    public void run()
    {
        while(true)
        {
            repaint();
            try{
                if(shifting<getWidth())
                {
                    if(filling<getHeight())
                        filling+=10;                    
                    else {
                        shifting+=20;
                    filling=0;
                    }
                }       
                Thread.sleep(50);
            }catch(Exception E){
                System.out.println("Exception caught");
            }

        }
    }

}

Answer 1

1. You only draw one rectangle in your paint method, and so it makes sense that only one will show.
2. If you need to draw more, do so, using a for loop that loops through perhaps a Rectangle ArrayList<Rectangle> .
3. Another way is to make shifting local and do a bit of simple math inside paintComponent to see what to draw and where. For instance, draw your completed bars inside of a for loop, for (int i = 0; i < filling / getHeight(); i++) { , and your yet to be completed bar up to filling % getHeight() .
4. You should not draw directly within a JApplet but rather in the paintComponent method of a JPanel.
5. A Swing Timer is easier to use than a thread (for me at least), and can be safer.

---

For example, this can be created by the code below:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.lang.reflect.InvocationTargetException;

import javax.swing.*;

@SuppressWarnings("serial")
public class FillingBar2 extends JApplet {
   @Override
   public void init() {
      try {
         SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
               FillingBarPanel fillingBarPanel = new FillingBarPanel();
               add(fillingBarPanel);
               add(new JButton(new StartAction(fillingBarPanel)), BorderLayout.PAGE_END);
               setSize(getPreferredSize());
            }
         });
      } catch (InvocationTargetException | InterruptedException e) {
         System.err.println("Big Problems");
         e.printStackTrace();
      }
   }
}

@SuppressWarnings("serial")
class StartAction extends AbstractAction {
   private FillingBarPanel fillingBarPanel;

   public StartAction(FillingBarPanel fillingBarPanel) {
      super("Start");
      putValue(MNEMONIC_KEY, KeyEvent.VK_S);
      this.fillingBarPanel = fillingBarPanel;
   }

   @Override
   public void actionPerformed(ActionEvent evt) {
      fillingBarPanel.start();
   }
}

@SuppressWarnings("serial")
class FillingBarPanel extends JPanel {
   private static final int BAR_WIDTH = 20;
   private static final int TIMER_DELAY = 100;
   private static final int PREF_W = 400;
   private static final int PREF_H = 250;
   private int filling = 0;
   private Timer timer;

   public FillingBarPanel() {
      timer = new Timer(TIMER_DELAY, new TimerListener());
   }

   public void start() {
      if (timer != null && !timer.isRunning()) {
         timer.start();
      }
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      int shifting = 0;
      for (int i = 0; i < filling / getHeight(); i++) {
         shifting = i * BAR_WIDTH;
         g.setColor(Color.GREEN);
         g.fillRect(shifting, 0, BAR_WIDTH, getHeight());

         g.setColor(Color.BLACK);
         g.drawRect(shifting, 0, BAR_WIDTH, getHeight());
      }
      shifting = BAR_WIDTH * (filling / getHeight());
      g.setColor(Color.GREEN);
      g.fillRect(shifting, getHeight() - (filling % getHeight()), BAR_WIDTH, getHeight());

      g.setColor(Color.BLACK);
      g.drawRect(shifting, getHeight() - (filling % getHeight()), BAR_WIDTH, getHeight());
   }

   private class TimerListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent evt) {
         filling += 10;
         repaint();
      }
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

}