Question

The applet should draw rectangles based that are dragged out using a MouseListener while a ball bounces around the applet.. The listener seems to work, printing out the location that the mouse is at works, and the ball is working just fine. However, as soon as the program is run and the mouse is dragged, the applet/browser freezes with no output to the console.

Here’s all of the code. I would just post the drawing method, but I think it might not just be in there.

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.util.Vector;

public class Bounce2 extends Applet implements ActionListener, AdjustmentListener, MouseListener, MouseMotionListener, Runnable
{
  //runtime variables
  boolean running = false;
  boolean kill = false;

  //buttons
  Button runbutton = new Button("Run");
  Button pausebutton = new Button("Pause");
  Button quitbutton = new Button("Quit");

  //text
  Label speedlabel = new Label("Speed");
  Label sizelabel = new Label("Size");

  Panel drawingpanel;

  //scrollbars
  private final int barHeight = 20, SLIDER_WIDTH = 10, MAXSPEED = 110, MINSPEED = 0, MAX_SIZE = 110, MIN_SIZE = 10;
  Scrollbar speedbar = new Scrollbar(Scrollbar.HORIZONTAL, MAXSPEED/2, SLIDER_WIDTH, MINSPEED, MAXSPEED);
  Scrollbar sizebar = new Scrollbar(Scrollbar.HORIZONTAL, MAX_SIZE/2, SLIDER_WIDTH, MIN_SIZE, MAX_SIZE);

  //drawn objs
  Ball ball;
  int size = 50;
  private Graphics obj;
  Image offscreen = null;
  Point loc = new Point(100,100); //location of the ball
  private Thread ballThread;

  //boundaries
  int boundx = 640;
  int boundy = 400;

  //directions
  int dx = 1; //1 = left, -1 = right
  int dy = 1; //1 = up, -1 = down

  //speed
  int speed = MAXSPEED/2;
  int delay = MAXSPEED - speed;

  //rectangle vector and associated things
  Vector r = new Vector();
  boolean flag = false;
  Point start, cur, end;

  //initialize the applet and draw everything
  public void init()
  {
    double colWeight[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols
    double rowWeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows
    int colWidth[] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1};//15 cols
    int rowHeight[] = {1,1,1,1,1,1,1,1,1,1}; //10 rows
    GridBagConstraints c = new GridBagConstraints();
    GridBagLayout gbl = new GridBagLayout();
    gbl.rowHeights = rowHeight;
    gbl.rowWeights = rowWeight;
    gbl.columnWeights = colWeight;
    gbl.columnWidths = colWidth;
    c.anchor = GridBagConstraints.CENTER;

    setBounds(0,0,480,640);
    setLayout(new BorderLayout());
    Panel controlpanel = new Panel();
    controlpanel.setLayout(gbl);
    controlpanel.setSize(640,80);

    drawingpanel = new Panel();
    drawingpanel.setSize(640,400);
    ball = new Ball();
    drawingpanel.setLayout(new BorderLayout());
    drawingpanel.add("Center",ball);

    //speed scrollbar
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 3;
    c.gridheight = 1;
    c.gridx = 1;
    c.gridy = 7;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.speedbar,c);

    //run button
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 2;
    c.gridheight = 1;
    c.gridx = 5;
    c.gridy = 7;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.runbutton,c);

    //pause button
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 2;
    c.gridheight = 1;
    c.gridx = 8;
    c.gridy = 7;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.pausebutton,c);

    //size scrollbar
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 3;
    c.gridheight = 1;
    c.gridx = 11;
    c.gridy = 7;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.sizebar,c);

    //speed text label
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 3;
    c.gridheight = 1;
    c.gridx = 1;
    c.gridy = 8;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.speedlabel,c);

    //size text label
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 3;
    c.gridheight = 1;
    c.gridx = 11;
    c.gridy = 8;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.sizelabel,c);

    //quit button
    c.weightx = 1;
    c.weighty = 1;
    c.gridwidth = 3;
    c.gridheight = 1;
    c.gridx = 6;
    c.gridy = 9;
    c.fill= GridBagConstraints.HORIZONTAL;
    gbl.setConstraints(this.quitbutton,c);

    //add to the screen
    controlpanel.add(this.speedbar);
    controlpanel.add(this.runbutton);
    controlpanel.add(this.pausebutton);
    controlpanel.add(this.sizebar);
    controlpanel.add(this.speedlabel);
    controlpanel.add(this.sizelabel);
    controlpanel.add(this.quitbutton);

    //add listners
    speedbar.addAdjustmentListener(this);
    runbutton.addActionListener(this);
    pausebutton.addActionListener(this);
    sizebar.addAdjustmentListener(this);
    quitbutton.addActionListener(this);
    ball.addMouseListener(this);
    ball.addMouseMotionListener(this);

    //add the panels
    add("South", controlpanel);
    add("Center", drawingpanel);

    //drawing paramaters
    loc = new Point(loc.x+dx, loc.y+dy);
  }

  public void start()
  {
    if (ballThread == null)
    {
      ballThread = new Thread(this);
      ballThread.start();
    }
  }

  public void run()
  {
    Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    while (!kill)
    {
      if (running)
      {
        ball.repaint();
      }
      try
      {
        Thread.sleep(delay);
      }
      catch(InterruptedException e){System.err.println("Interrupted.");}
    }
    stop();
  }

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

  //class to handle animations
  class Ball extends Canvas
  {     
    public void move()
    {
      //if it will hit the right or left, flip the x direction and set it
      if (loc.x+size >= boundx || loc.x <= 0)
      { dx *= -1; }
      loc.x += dx;
      //if it will hit the top or bottom, flip the y direction and set it
      if (loc.y+size >= boundy || loc.y <= 0)
      { dy *= -1; }
      loc.y += dy;
    }

    public void update(Graphics g)
    {
      super.update(g);
      Graphics buffer;
      if (offscreen == null)
      {
        offscreen = createImage(getWidth(), getHeight());
      }
      buffer = offscreen.getGraphics();
      buffer.setColor(getBackground());
      buffer.fillRect(loc.x,loc.y,boundx, boundy);
      mypaint(buffer);
      g.drawImage(offscreen, 0, 0, this);

    }

    public void mypaint(Graphics g)
    {
      //update loc
      move();

      //draw
      g.setColor(Color.BLACK);
      g.drawOval(loc.x, loc.y, size, size);
      g.fillOval(loc.x, loc.y, size, size);

      if (flag)
      {
        if (!r.isEmpty())
        {
            int i = 0;
            while (i <= r.size())
            {
                g.drawRect(start.x,start.y,(cur.x-start.x),(cur.y-start.y));
                g.setColor(Color.gray);
                g.fillRect(start.x,start.y,(cur.x-start.x),(cur.y-start.y));
            }
          System.err.println(start + ", " + cur);
        }
      }
    }
  }


    public void mouseClicked(MouseEvent m)
    {
        Point p = m.getPoint();
        //if p intersects rect in r, remove all r
    }

    public void mousePressed(MouseEvent m)
    {
        flag = true;
        start = m.getPoint();
    }

    public void mouseDragged(MouseEvent m)
    {
        if (flag == true)
        {
            cur = m.getPoint();
        }
    }

    public void mouseReleased(MouseEvent m)
    {
        end = m.getPoint();
        flag = false;
    r.add(new Rectangle(start.x,start.y,end.x,end.y));
    } 

    public void mouseEntered(MouseEvent m){}
    public void mouseExited(MouseEvent m){}
    public void mouseMoved(MouseEvent m){}

  public void actionPerformed(ActionEvent e)
  {
    Object source = e.getSource();
    if (source == this.runbutton)
    {
      running = true;
    }
    else if (source == this.pausebutton)
    {
      running = false;
    }
    else if (source == this.quitbutton)
    {
      //kill processes
      kill = true;
      //remove listeners
      stop();
    }
  }

  public void adjustmentValueChanged(AdjustmentEvent e)
  {
    Object source = e.getSource();
    //set the new size.
    if (source == sizebar)
    {
      //check for clipping
      int newsize = sizebar.getValue();

      // x
      if (loc.x+newsize >= boundx)
      {
        newsize = boundx - loc.x - 1;
        sizebar.setValue(newsize);
      }

      // y
      if (loc.y+newsize >= boundy + 100)
      {
        newsize = boundy+100 - loc.y - 1;
        sizebar.setValue(newsize);
      }
      size = newsize;
    }
    if (source == speedbar)
    {
      speed = speedbar.getValue();
      delay = MAXSPEED - speed;
    }
  }

  public void stop()
  {
    this.speedbar.removeAdjustmentListener(this);
    this.runbutton.removeActionListener(this);
    this.pausebutton.removeActionListener(this);
    this.sizebar.removeAdjustmentListener(this);
    this.quitbutton.removeActionListener(this);
    this.removeMouseListener(this);
    this.removeMouseMotionListener(this);
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
  }
}   

Answer 1

Well, there’s your probelm…

int i = 0;
while (i <= r.size()) {
    g.drawRect(start.x, start.y, (cur.x - start.x), (cur.y - start.y));
    g.setColor(Color.gray);
    g.fillRect(start.x, start.y, (cur.x - start.x), (cur.y - start.y));
}

You have an infinite loop. i will never be anything other then 0…

While we’re picking on it i <= r.size() will also cause problems, as the Vector is 0 based (that is 0-size() – 1).

Try someting like;

for (int i = 0; i < r.size(); i++) {
    g.drawRect(start.x, start.y, (cur.x - start.x), (cur.y - start.y));
    g.setColor(Color.gray);
    g.fillRect(start.x, start.y, (cur.x - start.x), (cur.y - start.y));
}

Instead