Use of Vector in undo operation ?

Question

Hello,
I am developing simple paint program. And want to use undo redo operation for drawing in drawing canvas. Actually I have done it with the help of Vector. But the problem is that it is not working properly. The first drawn shape is not removing with this operation and also the problem is that When i am using CTRL+Z for undoing last drawing. It is not removing last drawn shape with first undo operation. Let me know that what is the exact problem in my coding. I am not fully java programmer. So please tell me what to do for that. I want to draw n level of drawing on drawing canvas and also want to perform n level (first drawn shape) undo actions. And also want to know how to make redo button for same coding only use of Vector or ArrayList.
My code is here:
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
import java.util.*;
public class PaintUndo extends JFrame
     Display pan = new Display();
public PaintUndo()
     addWindowListener(new WindowAdapter()
    {     public void windowClosing(WindowEvent ev)
          {     dispose();
               System.exit(0);}});
     getContentPane().add("Center",pan);
       setBounds(1,1,600,400);
     JMenuBar  menu = new JMenuBar();;
     JMenu     submenu;
     JMenuItem item, redo;
     submenu = new JMenu("Edit");     
     item = new JMenuItem("UnDo");
    item.setMnemonic(KeyEvent.VK_Z);
        item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Z, ActionEvent.CTRL_MASK));
     item.addActionListener((ActionListener)pan);
     submenu.add(item);   
     menu.add(submenu);
     getContentPane().add("North",menu);
     setVisible(true);
public class Display extends JComponent implements MouseMotionListener, MouseListener, ActionListener
     Vector   saves = new Vector();
     BufferedImage image = null;
     Graphics ig;
     Graphics pg;
     Point point;
    int x1=0;
    int y1=0;
public Display()
     setBackground(Color.pink);
     addMouseMotionListener(this);
    addMouseListener(this);
public void paintComponent(Graphics g)
     if (image == null)
          image = (BufferedImage) createImage(800,600);
          ig = image.createGraphics();
          ig.setColor(Color.white);
          ig.fillRect(0,0,800,600);
          ig.setColor(Color.blue);
          pg = getGraphics();
          pg.setColor(Color.blue);
     g.drawImage(image,0,0,this);
public void mouseDragged(MouseEvent e)
        int x2 = e.getX(); int y2 = e.getY();
            Graphics gr = image.getGraphics();
               gr.drawLine(x1, y1, x2, y2);
            repaint();
            x1 = x2; y1 = y2;
public void mouseMoved(MouseEvent e)
public void actionPerformed(ActionEvent a)
     if (a.getActionCommand().equals("UnDo") && saves.size() > 0)
          ig.drawImage((Image)saves.remove(saves.size()-1),0,0,null);
          repaint();
        public void mouseClicked(MouseEvent e) {
            System.out.println("mouse clicked....");
        public void mousePressed(MouseEvent e) {
            System.out.println("mouse pressed....");
            x1 = e.getX();
               y1 = e.getY();
        public void mouseReleased(MouseEvent e) {
            System.out.println("mouse released....");
           Image tmg = createImage(800,600);
          Graphics tg = tmg.getGraphics();
          tg.drawImage(image,0,0,null);
          saves.add(tmg);
        public void mouseEntered(MouseEvent e) {
        public void mouseExited(MouseEvent e) {
public static void main (String[] args)
     new PaintUndo();
}This is complete code for undoing.
Any help will be appreciated.
Thanks in advance.
Manveer

Answer 1

The example code is set up for a protocol completely different than what you are doing, so you can't simply copy it and hope it works.  The example code expects that the other side will send a 4-byte header containing the number of data bytes that follow, then send the data.  The example code first reads that 4-byte header, casts it to an integer, and reads that number of bytes (the second Bluetooth Read).
When you run this with your device, the first read gets your 4 bytes - FF FF 22 33 - and converts that to an integer.  0xFFFF2233 is decimal 4294910515.  So you then try to read this huge number of bytes and you get an error - looks like error 1, an input parameter is invalid, because you can't read 4GB at once.  You can probably get your code working with a single Bluetooth Read, with a 1 second timeout (because you have a 1 second delay between packets).  You'll want to wire in some number of bytes to read that is at least the size of the largest packet you ever expect, but don't use a ridiculously huge number that generates an error.  LabVIEW will return as many bytes as are available when the timeout expires, even if it isn't as many as you asked to read (you might also get a timeout error, though, which you'll need to clear).  You can then do whatever you need to do with that data - search for FF FF, typecast anything after that to array of U16, display it. 
The output of the Bluetooth Read is a string, but it's not text - it's exactly the bytes that were sent.  The Y with the dots over it is the way ASCII 255 (0xFF) displays (at least in that font).  ASCII 34 (0x22) is ", and ASCII 51 (0x33) is the number 3.