Develop Reference

How to implement a KeyListener to an object in a JFrame?

I'm attempting to make Frogger in java for a school project but I'm having a lot of difficulties setting up KeyListener for the actual frog character.
I've tried setting up key bindings, requesting focus for the JPanel and JFrame, moving around where the character is initiated but nothing has seemed to work. This is the remnants of my attempts.
This is the program that runs my game.
import javax.swing.*;
public class Frogger
{
JFrame frame = new JFrame("Frogger");
CPT c = new CPT();
public Frogger()
{
frame.setBounds(0,0,700,500);
frame.setResizable(false);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(c);
}
public static void main(String[] args){
new Frogger();
}
}
The main game
public CPT() {
setLayout(new BorderLayout());
label = new JLabel("Frogger");
frame1 = new JFrame("Main");
label.setFont(new Font("Serif", Font.BOLD,50));
label.setBounds(275,10,250,250);
button1 = new JButton("PLAY");
button1.setBounds(300,350,100,50);
button1.setOpaque(false);
button1.setVisible(true);
this.setOpaque(false);
this.setLayout(null);
this.add(label);
button1.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame1.setVisible(true);
frame1.setSize(700,500);
frame1.setResizable(false);
frame1.setFocusable(false);
button1.setVisible(false);
frame1.add(new TrainCanvas());
frame1.add(p1);
p1.requestFocus();
}
});
this.add(button1); }
This is the TrainCanvas class that Draws the cars in the games as well as the frog
class TrainCanvas extends JComponent
{
private int lastX = 0;
private int lastX_1 = 0;
private int lastX_2 = 0;
public TrainCanvas() {
Thread animationThread = new Thread(new Runnable() {
public void run() {
while (true) {
repaint();
try {Thread.sleep(10);} catch (Exception ex) {}
}
}
});
animationThread.start();
}
public void paintComponent(Graphics g) {
Graphics2D gg = (Graphics2D) g;
//Draws Train 1
int w = getWidth();
int h = getHeight();
int trainW_1 = 100;
int trainH_1 = 5;
int trainSpeed_1 = 3;
int x = lastX + trainSpeed_1;
if (x > w + trainW_1) {
x = -trainW_1;
}
gg.setColor(Color.BLACK);
gg.fillRect(x, h/2 + trainH_1, trainW_1, trainH_1);
lastX = x;
Graphics2D g3 = (Graphics2D) g;
frog = new Rectangle(f_x,f_y,25,25);
g3.fill(frog);
g3.setColor(Color.GREEN);
}
}
Finally, the Key Listener
public void keyPressed(KeyEvent e)
{
if(e.getKeyCode()== KeyEvent.VK_UP)
{
CPT.f_y -= 100;
repaint();
}
else if(e.getKeyCode()== KeyEvent.VK_RIGHT)
{
CPT.f_x += 100;
repaint();
}
else if(e.getKeyCode() == KeyEvent.VK_LEFT)
{
CPT.f_x -= 100;
repaint();
}
else if(e.getKeyCode()==KeyEvent.VK_DOWN)
{
CPT.f_y += 100;
repaint();
}
else {}
}
public void keyReleased(KeyEvent e) {}
public void keyTyped(KeyEvent e) {}
}
The program runs perfectly fine without giving me any errors, which is making this troublesome. Whenever it gets to the main game window, none of the keys seem to work.

how can i make my buttons work? java [duplicate]

This question already has answers here:
Non-static variable cannot be referenced from a static context
(15 answers)
Closed 4 years ago.
I know there are many questions out there regarding action listeners etc.
However, none can help me with my specific issue...no matter which way I try to do it I always get an error.
Here is my simple bouncing ball program:
public class ControlledBall extends JPanel implements Runnable {
int diameter;
long delay;
private int x;
private int y;
private int vx;
private int vy;
public ControlledBall(int xvelocity, int yvelocity) {
diameter = 30;
delay = 40;
x = 1;
y = 1;
vx = xvelocity;
vy = yvelocity;
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
g.setColor(Color.blue);
g.fillOval(x,y,30,30);
g.setColor(Color.black);
g2.drawOval(x,y,30,30); //draw
}
public void run() {
while(isVisible()) {
try {
Thread.sleep(delay);
} catch(InterruptedException e) {
System.out.println("Something Went Wrong!");
}
move();
repaint();
}
}
public void move() {
if(x + vx < 0 || x + diameter + vx > getWidth()) {
vx *= -1;
}
if(y + vy < 0 || y + diameter + vy > getHeight()) {
vy *= -1;
}
x += vx;
y += vy;
}
public void stop(){
x=0;
y=0;
}
public class Action implements ActionListener{
public void actionPerformed(ActionEvent e){
stop();
}
}
public static void main(String[] args) {
ControlledBall ball2 = new ControlledBall(12,2);
JFrame window = new JFrame("Controlled Ball");
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
JButton stop = new JButton("Stop");
stop.setSize(4,400);
stop.setVisible(true);
stop.setText("Stop");
// stop.addActionListener(new Action());
stop.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
}
});
window.add(stop);
JButton start = new JButton("Start");
start.setSize(100,100);
start.setVisible(true);
start.setText("Start");
window.add(start);
start.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
}
});
c.ipadx = 400;
c.ipady = 400;
c.gridx = 10;
c.gridy = 10;
window.add(ball2,c);
c.ipadx = 50;
c.ipady = 20;
c.gridx = 10;
c.gridy = 10;
window.pack();
window.setSize(600,600);
window.setLocation(250,200);
window.setVisible(true);
new Thread(ball2).start();
}
}
as you can see by the commented bits I've tried a few different techniques and none have worked. any advice would be greatly appreciated.
Thanks
The main error I get is:
non static field cannot be referenced from a static context
and I assume that's because I'm running it from the main method.

The first thing you really want to do is get rid of your run method (and your reliance on Runnable). This is really an inappropriate way to perform regular updates in Swing.
Swing is single threaded and NOT thread safe, your current approach risks dirty read/writes across thread boundaries.
Instead, you want to use a Swing Timer, see How to Use Swing Timers for more details.
The next thing you want to do is add a start method and update the stop method to support the use of a Swing Timer...
public class ControlledBall extends JPanel {
//...
private Timer timer;
public void stop() {
if (timer == null) {
return;
}
timer.stop();
timer = null;
x = 0;
y = 0;
}
public void start() {
if (timer != null) {
return;
}
timer = new Timer(delay, new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
move();
repaint();
}
});
timer.start();
}
Then, your start and stop buttons just need to be updated to call these methods...
stop.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
ball2.stop();
}
});
//...
start.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
ball2.start();
}
});

Putting sprites over background in a game

I'm having trouble loading a sprite into a game. I have the background done, but the sprite doesn't seem to be on the background. I want to assume you put it in the main constructor, but I don't think it will work.
package MyGamePKG;
import java.awt.BorderLayout;
public class GameJFrame extends JFrame {
private JPanel contentPane;
private int x,y,x_vel,y_vel;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
GameJFrame frame = new GameJFrame();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public GameJFrame() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 720, 520);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
GameJPanel Jpanel = new GameJPanel();
Jpanel.setBounds(0, 0, 720, 480);
contentPane.add(Jpanel);
Jpanel.setLayout(null);
JLabel lblNewLabel = new JLabel("New label");
lblNewLabel.setIcon(new ImageIcon(GameJFrame.class.getResource("/Resources/gamemap.png")));
lblNewLabel.setBounds(0, 0, 720, 480);
contentPane.add(lblNewLabel);
}
}
The JPanel class
package MyGamePKG;
import java.awt.BasicStroke;
public class GameJPanel extends JPanel implements ActionListener, KeyListener {
private int frameRate = 30;
private int x=0;
private int y=460;
private int x_vel, y_vel;
private Image map;
private Image character;
/**
* Create the panel.
*/
public GameJPanel() {
character = new ImageIcon(getClass().getResource("/resources/sprite-concepts.png")).getImage();
this.addKeyListener(this);
this.setFocusable(true);
Timer timer = new Timer(30, this);
timer.start();
}
#Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
RenderingHints rh = new RenderingHints( RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHints(rh);
this.setOpaque(false);
myDrawBoxOvalsandRect(x,y,100,g2d);
//myDrawArc(x+25,y+40,50,50,550,170,g2d);
} // paintComponent
public void myDrawBoxOvalsandRect( int x, int y, int scale, Graphics my_g)
{
my_g.setColor(Color.cyan);
my_g.fillOval(x, y, 15, 15); //face
}
public void myDrawArc(int x, int y, int height, int width, int angle1, int angle2, Graphics my_g)
{
my_g.setColor(Color.red);
my_g.drawArc(x, y, 50, 50, 550, 170); //happy face
}
#Override
public void keyPressed(KeyEvent e) {
// TODO Auto-generated method stub
int c = e.getKeyCode();
if(c == KeyEvent.VK_LEFT)
{
x_vel = -2;
y_vel = 0;
}
if(c == KeyEvent.VK_UP)
{
x_vel = 0;
y_vel = -2;
}
if( c == KeyEvent.VK_RIGHT)
{
x_vel = 2;
y_vel = 0;
}
if( c == KeyEvent.VK_DOWN)
{
x_vel = 0;
y_vel = 2;
}
repaint();
}
#Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
x_vel = 0;
y_vel = 0;
repaint();
}
#Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
}
#Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
if(x < 0)
{
x_vel = 0;
x = 0;
}
if(x > 720)
{
x_vel = 0;
x = 720;
}
if(y < 0)
{
y_vel = 0;
y = 0;
}
if(y > 480)
{
y_vel = 0;
y = 480;
}
x = x + x_vel;
y = y + y_vel;
repaint();
}
}

I suspect a number of things...
It's possible that the z-ordering of the components is rendering the background over the foreground components
The reliance on null layouts means that it's possible the window borders are taking up more space then you are allowing for, covering up portions of the content.
Don't rely on a null layout and guess work. Each platform/Look and Feel has different requirements when it comes to the frame border (amongst other things). Instead, you should consider...
Overriding getPreferredSize to provide better sizing hints
Use an OverlayLayout manager
Use JFrame#pack to pack the frame around the content instead of using setBounds
Consider painting the entire game state using a single paintComponent method, this would mean rendering the background, middleground and foreground within GameJPanel's paintComponent.
The benefit of this, is you gain complete control over the z-ordering process.
You should consider using key bindings over using KeyListener as it does not suffer from the same focus related issues and provides you with finer control over determining the level of focus that the component will raise key events

Reference of graphics 2d object doesn't work in orphan Thread

I am trying to design a simple game using Graphics2D in a JPanel. I am able to draw normal objects by overriding the paintComponent() method. But when I reference the Graphics2D object inside a orphan Thread, it does not work. Where am I going wrong?
public void paintComponent(Graphics g) {
super.paintComponent(g);
g2d = (Graphics2D) g;
g2d.drawString("sample",60,100); //Works fine
if(<Certain Condition>){
new Thread(new Runnable(){
//Some Code Here
public void run() {
try{
g2d.drawString("sample2",60,100); //Does not work.. :(
System.out.println("Test Print"); //Shows Output
}
catch (Exception e)
{
}
}
}).start();
}
}
Here is the complete code for reference. This is essentially a 'ping pong ball' game. Its working well but I am not able to highlight an increase in score when the ball hits the striker. The important part of code is highlighted. It's SSCCE.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Random;
public class MovingBall extends JPanel {
int XPos, YPos;
int speedX, speedY;
int diameter;
private JButton jButton1 = new JButton();
private JButton jButton2 = new JButton();
private JLabel jLabel1 = new JLabel();
private static Timer timer;
private static MovingBall movingball;
private int w,h;
private int strikerHeight;
private int strikerWidth;
private int score;
private boolean isBallMoving;
int strikerYPos;
Graphics2D g2d;
public MovingBall() {
//Striker Properties
strikerHeight = 100;
strikerWidth = 20;
strikerYPos = strikerHeight/2;
//Ball Properties
isBallMoving = false;
XPos = strikerWidth + 5;
YPos = 0;
Random r = new Random();
speedX = 2+ Math.abs(r.nextInt()) % 5;
speedY = 2+ Math.abs(r.nextInt()) % 5;
diameter = 50;
//UI Objects
try {
jbInit();
} catch (Exception e) {
e.printStackTrace();
}
movingball = this; //Helps to access the current class object in inner classes
//Create a timer for animation
timer = new Timer(1, new ActionListener() {
public void actionPerformed(ActionEvent evt) {
movingball.repaint();
}
});
timer.start();
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g2d = (Graphics2D) g;
Dimension size = getSize();
Insets insets = getInsets();
w = size.width - insets.left - insets.right;
h = size.height - insets.top - insets.bottom;
//Paint the striker
g2d.setColor(Color.DARK_GRAY);
if(strikerYPos < strikerHeight/2) //Top End
g2d.fillRect(0,0, strikerWidth, strikerHeight);
else if(strikerYPos > (h-strikerHeight/2)) //Bottom End
g2d.fillRect(0,h-strikerHeight, strikerWidth, strikerHeight);
else //Anywhere in the middle
g2d.fillRect(0,strikerYPos - (strikerHeight/2), strikerWidth, strikerHeight);
//Paint the ball
if (isBallMoving) {
XPos += speedX;
YPos += speedY;
g2d.drawOval(XPos, YPos, diameter,diameter);
if((XPos+diameter) >= w)
{
//speedX *= -1;
speedX = ((int)Math.signum((double)speedX))*(-1) * (2+ Math.abs(new Random().nextInt()) % 5);
XPos = w-diameter-1;
}
if(XPos <= strikerWidth)
{
if((YPos+diameter/2) >= (strikerYPos-strikerHeight/2) && (YPos+diameter/2) <= (strikerYPos+strikerHeight/2))
{
score++;
//////////////////////////////////////////////////////////////////////
/////THIS IS THE PART TO FOCUS ON///////////////////////////////////////
/////WHEN THE BALL HITS THE STRIKER, I SHOW A '+1' TEXT FADING UPWARDS FROM THE POINT OF HIT
/////(THIS IS TO HIGHLIGHT A +1 INCREASE IN SCORE)///////////////////
//////NOW SINCE THE BALL MAY HIT THE STRIKER AGAIN BEFORE THE PREVIOUS +1 HAS COMPLETELY FADED,
//////I HAVE MADE THIS SIMPLE THREAD TO CREATE A +1 EVERY TIME THERE IS A HIT. SO THERE CAN BE MULTIPLE
//////+1 ON THE SCREEN.
//-------------------------------SADLY, SOMETHING IS WRONG-------------------
//Print a '+1' to show score increase
new Thread(new Runnable(){
int yStart = strikerYPos;
int fadeLength = 0;
Timer pointTimer;
int MAX_FADE_LEN = 50;
public void run() {
try
{
pointTimer = new Timer(1, new ActionListener() {
public void actionPerformed(ActionEvent evt) {
if(fadeLength >= MAX_FADE_LEN)
pointTimer.stop();
g2d.setColor(new Color(0,0,0,255));
g2d.setFont(new Font("Times",Font.BOLD,20));
g2d.drawString("+1",60,yStart - fadeLength);
g2d.drawOval(100,100,50,50);
System.out.println("Drawn +1 at x = " + 60 + " y = " + (yStart - fadeLength));
fadeLength++;
}
});
pointTimer.start();
}
catch (Exception e)
{
}
}
}).start();
////////////////THREAD ENDS HERE//////////////////////
}
else
{
score--;
}
//SHOW THE SCORE ON THE LABEL
jLabel1.setText("Score: " + score);
speedX = ((int)Math.signum((double)speedX))*(-1) * (2+ Math.abs(new Random().nextInt()) % 5);
XPos = strikerWidth+1;
}
if(YPos <= 0)
{
speedY = ((int)Math.signum((double)speedY))*(-1) * (2+ Math.abs(new Random().nextInt()) % 5);
YPos = 0;
}
if((YPos+diameter) >= h)
{
speedY = ((int)Math.signum((double)speedY))*(-1) * (2+ Math.abs(new Random().nextInt()) % 5);
YPos = h-diameter;
}
} else {
g2d.drawOval(XPos,YPos,diameter,diameter);
return;
}
}
public static void main(String[] args) {
JFrame frame = new JFrame("Magic Ball");
movingball = new MovingBall();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(movingball);
frame.setSize(450, 700);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private void jbInit() throws Exception {
jButton1.setText("Start");
jButton1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jButton1_actionPerformed(e);
}
});
jButton2.setText("Stop");
jButton2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
jButton2_actionPerformed(e);
}
});
jLabel1.setText("Score:0");
this.add(jButton1, null);
this.add(jButton2, null);
this.add(jLabel1, null);
this.setBackground(Color.white);
this.addMouseMotionListener(new MouseMotionListener() {
public void mouseMoved(MouseEvent e) {
int coordX = e.getX();
if(coordX < 200)
strikerYPos = e.getY();
}
public void mouseDragged(MouseEvent e) {
}
});
}
private void jButton1_actionPerformed(ActionEvent e) {
if(!isBallMoving)
isBallMoving = true;
}
private void jButton2_actionPerformed(ActionEvent e) {
isBallMoving = false;
}
}

everything inside paintComponent is repainted (automatically) on every mouse, key and internall methods implemented in API, then you thread probably never ended, there can be bunch of concurently Threads, nothing is repainted, displayed
output to the Swing GUI must be done on EDT
use Swing Timer instead of new Thread(new Runnable(){
call repaint()

I don't think many people would consider almost 250 LOC to be 'short' (though I must admit I was deliberately vague when writing the SSCCE document). OTOH I adapted my shorter source seen here to an animated example that shows a 'fade effect' on mouse clicks. Adapting it to your needs is left as an exercise for ..you.
This source shows how to change the drawn string over a period of 5 seconds. It uses the same Thread (the EDT) for both the main (bouncing ball) and fade animation.
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import javax.swing.*;
class ShapeCollision {
private BufferedImage img;
private Area walls;
int x;
int y;
int xDelta = 3;
int yDelta = 2;
ArrayList<Strike> strikes;
/**
* A method to determine if two instances of Area intersect
*/
public boolean doAreasCollide(Area area1, Area area2) {
boolean collide = false;
Area collide1 = new Area(area1);
collide1.subtract(area2);
if (!collide1.equals(area1)) {
collide = true;
}
Area collide2 = new Area(area2);
collide2.subtract(area1);
if (!collide2.equals(area2)) {
collide = true;
}
return collide;
}
ShapeCollision() {
int w = 400;
int h = 200;
img = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
final JLabel imageLabel = new JLabel(new ImageIcon(img));
x = w / 2;
y = h / 2;
strikes = new ArrayList<Strike>();
MouseListener strikeListener = new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
Strike s = new Strike(e.getPoint(),System.currentTimeMillis());
strikes.add(s);
}
};
imageLabel.addMouseListener(strikeListener);
walls = new Area(new Rectangle(0, 0, w, h));
ActionListener animate = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
animate();
imageLabel.repaint();
}
};
Timer timer = new Timer(50, animate);
timer.start();
JOptionPane.showMessageDialog(null, imageLabel);
timer.stop();
}
public void animate() {
Graphics2D g = img.createGraphics();
g.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g.setColor(Color.BLACK);
g.fillRect(0, 0, img.getWidth(), img.getHeight());
x += xDelta;
y += yDelta;
int s = 15;
Area player = new Area(new Ellipse2D.Double(x, y, s, s));
// Acid test of edge collision;
if (doAreasCollide(player, walls)) {
if (x + s > img.getWidth() || x < 0) {
xDelta *= -1;
}
if (y + s > img.getHeight() || y < 0) {
yDelta *= -1;
}
}
g.setColor(Color.ORANGE);
g.setColor(Color.YELLOW);
g.fill(player);
for (Strike strike : strikes) {
strike.draw(g);
}
g.dispose();
}
public static void main(String[] args) {
Runnable r = new Runnable() {
#Override
public void run() {
new ShapeCollision();
}
};
// Swing GUIs should be created and updated on the EDT
// http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html
SwingUtilities.invokeLater(r);
}
}
class Strike {
private Point point;
private long started;
private final long DURATION = 5000;
private boolean expired = false;
Strike(Point point, long time) {
this.point = point;
started = time;
}
public void draw(Graphics g) {
long now = System.currentTimeMillis();
long age = now - started;
if (age>DURATION) {
expired = true;
return;
}
double fraction = 1d-((double)age/(double)DURATION);
int alpha = (int)(fraction*255d);
Color c = new Color(255,255,255,alpha);
g.setColor(c);
String s = point.x + "," + point.y;
g.drawString( s, point.x, point.y );
}
public boolean isExpired() {
return expired;
}
}

As i understand - you save the Graphics2D object into g2d variable and trying to paint something onto it from a separate thread later? If so - don't do it. It is a really bad thing to do. Really.
If you want to modify (animate/change) whatever is painted on your component - simply change the data/model which affects the painting and than repaint the whole component or its modified part (any rectangle within the component bounds).
For example in your example case - keep painted string coordinates outside the paint method and modify them in a separate thread and then just call repaint on the component each time you change them. With each repaint string will be painted at the updated coordinates.
Also note that repaint might be called outside of the EDT (Event Dispatch Thread) as it will perform the actual repaint in EDT anyway.
Here is some random example of animation:
public class AnimationTest
{
private static List<Point> locationData = new ArrayList<Point> ();
private static List<Boolean> directionData = new ArrayList<Boolean> ();
public static void main ( String[] args )
{
locationData.add ( new Point ( 5, 25 ) );
directionData.add ( true );
final JComponent canvas = new JComponent ()
{
protected void paintComponent ( Graphics g )
{
super.paintComponent ( g );
Graphics2D g2d = ( Graphics2D ) g;
for ( int i = 0; i < locationData.size (); i++ )
{
Point p = locationData.get ( i );
g2d.drawString ( "Some string #" + i, p.x, p.y );
}
}
};
canvas.addMouseListener ( new MouseAdapter ()
{
public void mousePressed ( MouseEvent e )
{
locationData.add ( e.getPoint () );
directionData.add ( true );
canvas.repaint ();
}
} );
JFrame frame = new JFrame ();
frame.getContentPane ().setLayout ( new BorderLayout () );
frame.getContentPane ().add ( canvas );
frame.setSize ( 500, 500 );
frame.setLocationRelativeTo ( null );
frame.setDefaultCloseOperation ( JFrame.EXIT_ON_CLOSE );
frame.setVisible ( true );
Timer timer = new Timer ( 1000 / 48, new ActionListener ()
{
public void actionPerformed ( ActionEvent e )
{
for ( int i = 0; i < locationData.size (); i++ )
{
Point p = locationData.get ( i );
if ( directionData.get ( i ) )
{
if ( p.y < canvas.getHeight () - 1 )
{
p.y += 1;
}
else
{
directionData.set ( i, false );
}
}
else
{
if ( p.y > 20 )
{
p.y -= 1;
}
else
{
directionData.set ( i, true );
}
}
}
canvas.repaint ();
}
} );
timer.start ();
}
}
You can find here:
Data lists on which painting and animation are based with single initial element
Data modification through mouse interaction
Proper canvas update on any data changes
Example is not too optimized, but should be enough to understand the concept.

Print the graphicsobject, if it changes between calls in paintComponent it means the one you are passing to the orphan thread is a dead object which swing doesn't use anymore for painting on the current component.

Swing is a platform-independent, Model-View-Controller GUI framework for Java, which follows a single-threaded programming model.
You should use dispatcher. http://en.wikipedia.org/wiki/Event_Dispatch_Thread

Java Swing: JPanels painting over each other

Alright, so I have two JFrames each with a different implementation of JPanel sitting inside of them. When I call repaint() on the JPanels, what is painted on one JPanel also becomes painted on the other JPanel.
I know I could take care of this by calling something like g.clearRect(), but there are too many components to repaint every time.
Any idea why this is happening?
//This makes the two JFrames and JPanels, sets everything up
public void makeSpaceSimulation() {
int dimen = 10000;
int scale = 20;
int numOfClusters = 30;
int planPerCluster = 2000;
SpaceShip s = new SpaceShip(dimen, scale);
QuadTree t = new QuadTree(dimen, 20);
new PlanetCreationTest(t, dimen, scale, numOfClusters, planPerCluster);
makeMap(dimen, scale, s, t);
makePOV(s, t, scale, dimen);
}
public void makeMap(int dimen, int scale, SpaceShip s, QuadTree t) {
final JFrame f = new JFrame();
f.setSize(dimen / scale, dimen / scale);
f.setLocation(0, 0);
f.setTitle("Map Panel");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mapP = new MapPanel(scale, s, dimen);
mapP.setLayout(new BorderLayout());
mapP.addTree(t);
f.add(mapP);
f.setVisible(true);
Insets i = f.getInsets();
f.setSize(dimen / scale + (i.left + i.right) + 2, dimen / scale
+ (i.top + i.bottom) + 2);
Thread th = new Thread() {
public void run() {
while (true) {
mapP.repaint();
}
}
};
th.start();
}
public void makePOV(final SpaceShip s, QuadTree t, int scale, int dimen) {
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
JFrame f = new JFrame();
f.setSize(500, 500);
f.setLocation(screenSize.width - 500, 0);
f.setTitle("POV Panel");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
povP = new POVPanel(s, scale, dimen);
povP.setLayout(new BorderLayout());
povP.addTree(t);
povP.setFocusable(true);
povP.addKeyListener(new KeyListener() {
#Override
public void keyPressed(KeyEvent arg0) {
final int i = arg0.getKeyCode();
Thread th = new Thread() {
public void run() {
if (i == 39) {
s.moveRight();
} else if (i == 37) {
s.moveLeft();
} else if (i == 40) {
s.moveDown();
} else if (i == 38) {
s.moveUp();
}
try {
Thread.sleep(500);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
th.start();
}
#Override
public void keyReleased(KeyEvent arg0) {
}
#Override
public void keyTyped(KeyEvent arg0) {
}
});
f.add(povP);
f.setVisible(true);
Insets i = f.getInsets();
f.setSize(dimen / 20 + (i.left + i.right) + 2, dimen / 20
+ (i.top + i.bottom) + 2);
Thread th = new Thread() {
public void run() {
while (true) {
povP.repaint();
}
}
};
th.start();
}
//here's the MapPanel
public class MapPanel extends JPanel {
private QuadTree q;
private int scale;
private int dimen;
private SpaceShip s;
private boolean firstDraw;
public MapPanel(int scale, SpaceShip s, int dimen) {
this.dimen = dimen;
q = new QuadTree(0, 0);
this.scale = scale;
this.s = s;
firstDraw = true;
}
public void addTree(QuadTree q) {
this.q = q;
}
public void paintComponent(Graphics g) {
if (firstDraw) {
q.draw(g, scale, new Point(0, 0));
s.drawScaledGeometry(g);
System.out.println("Totally drew that");
firstDraw = false;
} else {
g.clearRect(s.viewDistance.x/scale, s.viewDistance.y/scale,
s.viewDistance.width/scale, s.viewDistance.height/scale);
q.quadDraw(g, scale, s.viewDistance, new Point(0, 0));
s.drawScaledGeometry(g);
}
}
}
//and this is the POVPanel
public POVPanel(SpaceShip s, int scale, int dimen) {
super();
this.s = s;
// this.scale = scale;
this.dimen = dimen;
}
public void addTree(QuadTree q) {
this.q = q;
}
public void paintComponent(Graphics g) {
g.clearRect(0, 0, dimen / 20, dimen / 20);
q.quadDraw(g, 1, s.viewDistance, s.getMoved());
s.drawGeometry(g);
}

This is (one) of your problems...
public void paintComponent(Graphics g) {
if (firstDraw) {
q.draw(g, scale, new Point(0, 0));
s.drawScaledGeometry(g);
System.out.println("Totally drew that");
firstDraw = false;
} else {
g.clearRect(s.viewDistance.x/scale, s.viewDistance.y/scale,
s.viewDistance.width/scale, s.viewDistance.height/scale);
q.quadDraw(g, scale, s.viewDistance, new Point(0, 0));
s.drawScaledGeometry(g);
}
}
The Graphics context is shared during the paint cycle, meaning when you get it, you will be getting the same context used to paint all the other components on the screen.
You MUST call super.paintComponent(g), which will take care of preparing the graphics context for this component to start painting.
Update #1
Again...
public void paintComponent(Graphics g) {
super.paintComponent(g); // <-- Call me instead...
//g.clearRect(0, 0, dimen / 20, dimen / 20);
q.quadDraw(g, 1, s.viewDistance, s.getMoved());
s.drawGeometry(g);
}
Update #2
I'm also seriously concerned by this
while (true) {
mapP.repaint();
}
This could seriously impact the performance of you application. You DO NOT control the paint cycle, that's the responsibility of the repaint manager. The repaint manager will decide when a repaint is required. Calling repaint repetitively like this could actually cause the repaint manager to delay actually scheduling a paint cycle.
Much better to use a javax.swing.Timer, it's simpler and safer...
Timer timer = new Timer(25, new ActionListener() {
public void actionPerformed(ActionEvent evt) {
mapP.repaint();
}
});
timer.setRepeats(true);
timer.setCoalesce(true);
timer.start();
You might find reading through
Performing Custom Painting
Painting in AWT and Swing
Helpful
Update #3
Avoid KeyListener, it will only make you cry. Instead, use the key bindings API