My basic bouncing ball Applet should have a ball moving around according to the values in loc variable, but nothing shows up. Printing out loc shows that the numbers/math behind moving it around and bouncing off boundaries is indeed working as it should, but nothing shows up. Looking at examples online I didn’t see why my drawing/painting code wasn’t working as intended. Here’s what I have, issues are probably focused about halfway down where the Ball object is. I posted most of the program as it does compile/run if someone will run it.
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class Bounce2 extends Applet implements ActionListener, AdjustmentListener, 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");
//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 = speedbar.getValue();
int delay;
//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);
Panel drawingpanel = new Panel(null);
drawingpanel.setSize(640,400);
ball = new Ball();
drawingpanel.add(ball);
drawingpanel.setVisible(true);
//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);
//add the panels
add("South", controlpanel);
add("Center", drawingpanel);
//drawing paramaters
obj = drawingpanel.getGraphics();
loc = new Point(loc.x+dx, loc.y+dy);
setVisible(true);
validate();
}
public void start()
{
if (ballThread == null)
{
ballThread = new Thread(this);
ballThread.start();
repaint();
}
}
public void run()
{
Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
while (!kill)
{
if (running)
{
repaint();
}
try
{
Thread.sleep(delay);
}
catch(InterruptedException e){System.err.println("Interrupted.");}
}
stop();
}
//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;
setBounds(dx,dy,size,size);
}
public void paint(Graphics g)
{
update(g);
}
public void update(Graphics g)
{
Graphics buffer;
if (offscreen == null);
{
offscreen = createImage(boundx, boundy);
buffer = offscreen.getGraphics();
}
buffer.setColor(getBackground());
buffer.fillRect(loc.x,loc.y,boundx, boundy);
//update loc
move();
//draw
buffer.setColor(Color.black);
buffer.drawOval(loc.x, loc.y, size, size);
buffer.fillOval(loc.x, loc.y, size, size);
//draw rectangles out of vector
super.paint(g);
g.drawImage(offscreen, loc.x, loc.y, null);
}
}
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 - speedbar.getValue();
}
}
public void stop()
{
this.speedbar.removeAdjustmentListener(this);
this.runbutton.removeActionListener(this);
this.pausebutton.removeActionListener(this);
this.sizebar.removeAdjustmentListener(this);
this.quitbutton.removeActionListener(this);
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
}
}
This is modified version of your code that is running.