Develop Reference

Java game loop (painting) freezes my window

I'm changing "views" with cardLayout (this class has a JFrame variable). When a user clicks a new game button this happens:
public class Views extends JFrame implements ActionListener {
private JFrame frame;
private CardLayout cl;
private JPanel cards;
private Game game;
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
if (command.equals("New game")) {
cl.show(cards, "Game");
game.init();
this.revalidate();
this.repaint();
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
game.loop();
}
});
}
}
}
Game's loop method and heading of class:
public class Game extends JPanel implements KeyListener {
public void loop() {
while (player.isAlive()) {
try {
this.update();
this.repaint();
// first class JFrame variable
jframee.getFrame().repaint();
// first class JFrame variable
jframee.getFrame().revalidate();
Thread.sleep(17);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public void update() {
System.out.println("updated");
}
}
I'm painting using paintComponent()
public void paintComponent(Graphics g) {
System.out.println("paint");
...
}
Actually it's not painting anything. When I do not call loop() method (so it paints it just once) all images are painted correctly. But when I call loop() method, just nothing is happening in the window. (Even close button on JFrame doesn't work.)
How to fix that? (When I was creating JFrame inside game class everything worked fine, but now I want to have more views so I need JFrame in other class.)
Thanks.

Precursor: The Event Dispatch Thread (EDT).
Swing is single-threaded. What does this mean?
All processing in a Swing program begins with an event. The EDT is a thread that processes these events in a loop along the following lines (but more complicated):
class EventDispatchThread extends Thread {
Queue<AWTEvent> queue = ...;
void postEvent(AWTEvent anEvent) {
queue.add(anEvent);
}
#Override
public void run() {
while (true) {
AWTEvent nextEvent = queue.poll();
if (nextEvent != null) {
processEvent(nextEvent);
}
}
}
void processEvent(AWTEvent theEvent) {
// calls e.g.
// ActionListener.actionPerformed,
// JComponent.paintComponent,
// Runnable.run,
// etc...
}
}
The dispatch thread is hidden from us through abstraction: we generally only write listener callbacks.
Clicking a button posts an event (in native code): when the event is processed, actionPerformed is called on the EDT.
Calling repaint posts an event: when the event is processed, paintComponent is called on the EDT.
Calling invokeLater posts an event: when the event is processed, run is called on the EDT.
Everything in Swing begins with an event.
Event tasks are processed in sequence, in the order they are posted.
The next event can only be processed when the current event task returns. This is why we cannot have an infinite loop on the EDT. actionPerformed (or run, as in your edit) never returns, so the calls to repaint post paint events but they are never processed and the program appears to freeze.
This is what it means to "block" the EDT.
There are basically two ways to do animation in a Swing program:
Use a Thread (or a SwingWorker).
The benefit to using a thread is that the processing is done off the EDT, so if there is intensive processing, the GUI can still update concurrently.
Use a javax.swing.Timer.
The benefit to using a timer is that the processing is done on the EDT, so there is no worry about synchronization, and it is safe to change the state of the GUI components.
Generally speaking, we should only use a thread in a Swing program if there's a reason to not use a timer.
To the user, there is no discernible difference between them.
Your call to revalidate indicates to me that you are modifying the state of the components in the loop (adding, removing, changing locations, etc.). This is not necessarily safe to do off the EDT. If you are modifying the state of the components, it is a compelling reason to use a timer, not a thread. Using a thread without proper synchronization can lead to subtle bugs that are difficult to diagnose. See Memory Consistency Errors.
In some cases, operations on a component are done under a tree lock (Swing makes sure they are thread-safe on their own), but in some cases they are not.
We can turn a loop of the following form:
while ( condition() ) {
body();
Thread.sleep( time );
}
in to a Timer of the following form:
new Timer(( time ), new ActionListener() {
#Override
public void actionPerformed(ActionEvent evt) {
if ( condition() ) {
body();
} else {
Timer self = (Timer) evt.getSource();
self.stop();
}
}
}).start();
Here is a simple example demonstrating animation both with a thread and a timer. The green bar moves cyclically across the black panel.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class SwingAnimation implements Runnable{
public static void main(String[] args) {
SwingUtilities.invokeLater(new SwingAnimation());
}
JToggleButton play;
AnimationPanel animation;
#Override
public void run() {
JFrame frame = new JFrame("Simple Animation");
JPanel content = new JPanel(new BorderLayout());
play = new JToggleButton("Play");
content.add(play, BorderLayout.NORTH);
animation = new AnimationPanel(500, 50);
content.add(animation, BorderLayout.CENTER);
// 'true' to use a Thread
// 'false' to use a Timer
if (false) {
play.addActionListener(new ThreadAnimator());
} else {
play.addActionListener(new TimerAnimator());
}
frame.setContentPane(content);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
abstract class Animator implements ActionListener {
final int period = ( 1000 / 60 );
#Override
public void actionPerformed(ActionEvent ae) {
if (play.isSelected()) {
start();
} else {
stop();
}
}
abstract void start();
abstract void stop();
void animate() {
int workingPos = animation.barPosition;
++workingPos;
if (workingPos >= animation.getWidth()) {
workingPos = 0;
}
animation.barPosition = workingPos;
animation.repaint();
}
}
class ThreadAnimator extends Animator {
volatile boolean isRunning;
Runnable loop = new Runnable() {
#Override
public void run() {
try {
while (isRunning) {
animate();
Thread.sleep(period);
}
} catch (InterruptedException e) {
throw new AssertionError(e);
}
}
};
#Override
void start() {
isRunning = true;
new Thread(loop).start();
}
#Override
void stop() {
isRunning = false;
}
}
class TimerAnimator extends Animator {
Timer timer = new Timer(period, new ActionListener() {
#Override
public void actionPerformed(ActionEvent ae) {
animate();
}
});
#Override
void start() {
timer.start();
}
#Override
void stop() {
timer.stop();
}
}
static class AnimationPanel extends JPanel {
final int barWidth = 10;
volatile int barPosition;
AnimationPanel(int width, int height) {
setPreferredSize(new Dimension(width, height));
setBackground(Color.BLACK);
barPosition = ( width / 2 ) - ( barWidth / 2 );
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
int width = getWidth();
int height = getHeight();
int currentPos = barPosition;
g.setColor(Color.GREEN);
g.fillRect(currentPos, 0, barWidth, height);
if ( (currentPos + barWidth) >= width ) {
g.fillRect(currentPos - width, 0, barWidth, height);
}
}
}
}

What does update do? You probably shouldnt call game.loop() on the EDT. You are running a loop on EDT, your repaint wont ever be invoked since repaint queues an event on EDT and it seems kind busy. Try moving game.loop() to another thread
new Thread(new Runnable() {
#override
public void run() {
game.loop();
}
}).start();
This way you wont block the EDT while the repaint still gets to be executed on the EDT.

Move game.loop() method invocation to something like:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
game.loop()
}
});
Thanks.

Random background color in a loop (Java)

I want to change the background color of a panel each time repaint() is called. I'm having a hard time doing it with setBackground, so I wonder if a drawRect with the same dimensions as the frame will do the same job, or is this a no-no?
public class Artwork extends JPanel implements Runnable {
boolean running = false;
Random rng = new Random();
public Artwork() {
this.setOpaque(true);
}
public void Start() {
running = true;
Thread thread = new Thread(this);
thread.start();
}
public void Stop() {
running = false;
}
public void run() {
while (running = true) {
repaint();
try {
Thread.sleep(2500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
super.setBackground(randomColor());
}
public Color randomColor() {
int r = rng.nextInt(255);
int g = rng.nextInt(255);
int b = rng.nextInt(255);
return new Color(r, g, b);
}
With this the background color changes rapidly regardless of Thread.sleep

With this the background color changes rapidly regardless of Thread.sleep
Painting methods are for painting only!
Don't invoke methods (like setBackground()) that change the property of the component in the paintComponent() method. Swing components automatically repaint() themselves when a property is changed. This will cause an infinite loop as the component repaints itself again and again and again....
The solution is to invoke the setBackground() method in the Thread before invoking the repaint method.

Java - repaint JPanel 2 times in one method

This is simple version of my problem.
I have 3 classes:
public class TopographyFrame extends JFrame - simple JFrame with JPAnel and button
public class TopograpyPanel extends JPanel - JPanel to fill Rectangles
public class Siec - class to perform calculations and call repaint on JPAnale
in JPanel i overided paintComponent() method
public void paintComponent (Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
System.out.println(rectangles.length);
for(int i = 0 ; i < rectangles.length ; i++){
g2.setPaint(neurony[i].winner);
g2.fillRect((int)rectangles[i].x,(int)rectangles[i].y,(int)rectangles[i].width, (int)rectangles[i].height);
}
}
neurony - array of objects with field public Color winner
in class Siec i have reference to JPanel to repaint it
in class JFrame i have a button with private action listener:
class MyListener implements ActionListener{
Siec s;
public MyListener(Siec s){
this.s = s;
}
public void actionPerformed(ActionEvent arg0) {
try {
s.forPaint();
} catch (Exception e) {
e.printStackTrace();
}
}
method forPaint() in Siec looks like:
public void forPaint(){
setTopography();
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
setTopography();
}
public void setTopography() {
for (int i = 0; i < vector.colors.length; i++) {
neurony[i].winner = vector.colors[(int)(random() * 900 % vector.colors.length)];
}
panel.repaint();
}
vector.color is array of Colors
So my problem is: when i click a button i would like to JPanel repaint immediately and then after 3 second repaint one more time. Insted JPanel repaints only one time after 3s delay.
}

You can't sleep, wait, or otherwise pause on the event handling thread, ever. Doing so blocks all events from being processed, including painting events. Your first painting can't occur because you're sleeping on the event thread, preventing it from happening.
The right way to do any kind of animation -- even simple stuff like this -- is to create your own thread. That second thread can call repaint(), sleep for 3 seconds, then call repaint() again. The SwingWorker class is nominally a simpler way to do this, but in all honesty, beginners always find creating their own thread to be easier.

You are scheduling a repaint on the UI thread and then sleeping (blocking) the UI thread for 3seconds and then requesting another repaint again. Those two will either happen really close to each other after this method has finished (after 3 seconds) or be merged into one update (afterwards as well).
Instead of sleep(3000) and then calling your setTopography again you could schedule a setTopography call on the UI thread to happen after 3 seconds.
Have a look at the Swing Timer for example:
http://docs.oracle.com/javase/tutorial/uiswing/misc/timer.html
So something along the lines of:
javax.swing.Timer timer = new javax.swing.Timer(3000, new ActionListener() {
public void actionPerformed(ActionEvent e) {
setTopography();
}
});
timer.setRepeats(false);
timer.start();

Since your sleep is being performed on the Event Dispatch Thread, the repaint() event cannot be performed until the end of the wait. Do this instead:
private Timer timer = new Timer(); // use java.util.Timer
public void forPaint() {
setTopography();
timer.schedule(new TimerTask() {
#Override
public void run() {
setTopography();
}
}, 3000);
}
public void setTopography() {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
for (int i = 0; i < vector.colors.length; i++) {
neurony[i].winner = vector.colors[(int)(random() * 900 % vector.colors.length)];
}
panel.repaint();
}
});
}
Keep in mind that all modifications to a Swing component (e.g. your JPanel) must happen on the EDT.

Combining repaint() with Thread.Sleep()

What im trying to do is pretty simple, I want to show the steps of an algorithm on the screen, hence why im trying to combine repaint() with sleep(), but I am doing it wrong, Id love it if someone knows enough about it to firstly explain whats wrong with this code, and secondly, what do i do to make it work...
thanks!
in summery, what this code was meant to do is paint 10 red vertices, then balcken em one by one in intervals of 200 milliseconds.
here's the code:
public class Tester {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
ShowGUIGraph();
}
});
}
private static void ShowGUIGraph() {
JFrame f = new JFrame("something");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel p=new JPanel();
p.setLayout(new BorderLayout());
p.add(BorderLayout.CENTER,new SomePanel());
f.add(p);
f.setPreferredSize(new Dimension(800,600));
f.pack();
f.setVisible(true);
}
}
public class SomePanel extends JPanel {
private static final long serialVersionUID = 1L;
LinkedList<Vertex> vertices=new LinkedList<Vertex>();
public SomePanel () {
for (int i=0;i<10;i++) {
Vertex v=new Vertex(i);
v.setLocation(20+30*i, 20+30*i);
vertices.add(v);
}
traverseVerticesRecoursive(0);
traverseVerticesNonRecoursive();
}
public void traverseVerticesRecoursive(int i) {
if (i>=vertices.size()) return;
vertices.get(i).setColor(Color.black);
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
repaint();
traverseVerticesRecoursive(i+1);
}
public void traverseVerticesNonRecoursive() {
for (int i=0;i<10;i++) {
vertices.get(i).setColor(Color.red);
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
repaint();
}
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
for (int i=0;i<vertices.size();i++) {
vertices.get(i).paintVertex(g);
}
}
}
public class Vertex {
private int x,y,tag,r=20;
private Color color=Color.red;
Vertex (int i) {
tag=i;
}
public void setLocation(int x0,int y0) {
x=x0;
y=y0;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
public void setColor(Color c) {
color=c;
}
public boolean colorIs(Color c) {
return (color.equals(c));
}
public void paintVertex(Graphics g) {
g.setColor(color);
g.fillOval(x,y,r,r);
g.setColor(Color.BLACK);
g.drawOval(x,y,r,r);
g.drawString(""+tag, x+r/2, y+r/2+4);
}
public int getR() {
return r;
}
}

Do not sleep in the Event Dispatch Thread; this will cause the GUI to freeze. For animation, use an EDT-friendly utility class, such as javax.swing.Timer.

Just a few ideas that might make your code cleaner:
In your SomePanel class, put the traversing code in a method out of the constructor. Constructors are intended for initializing fields.
First launch your static GUI, then spawn a worker thread to do the updates via the previous method (this would be your small "engine"). In this thread is were you can call sleep.
In your traverseVerticesRecoursive method, do only the repaint on the UI thread, and the status update on your worker thread.
Tha main modification you should do is not to block the GUI thread with sleep calls, as they have told you in the first answer.

Thread.sleep is a long running task. When you a running such a task in the EDT it blocks all repaint requests from being executed. All repaint requests which are pending and which were sent during the sleep phase are queued for future processing.
As a result when the EDT comes out of the sleep phase it coalesce all such repaint request (if coalescing is enabled which is the default property) into a single repaint which gets executed. If coalescing is not enabled then all queued request are executed serially without any time gap in between. As a result it seems that the UI did not update.
To correct the situation use a timer which triggers periodically after specific intervals of time.

Guy, you could use a new Thread differ with EDT thread to make an animation. For example,
void play() {
Thread thread = new Thread() {
#Override
public void run() {
game();
}
};
thread.start();
}
void game() {
for (; ; ) {
switch (state) {
case GameData.ANIMATING:
// call some function as repaint() to update GUI
break;
case GameData.GAME_ENDED:
return;
default:
break;
}
diffTime = System.currentTimeMillis() - beforeTime;
sleepTime = delay - diffTime;
sleepTime = (sleepTime < 0) ? 0 : sleepTime;
Thread.sleep(sleepTime);
}
}

Added BufferedImage is only 2x2 pixels

I have a script that cycles (almost like a slideshow) through a Vector object (flipBook), using a Thread (animationThread), and adds them to a JPanel. However, the added image is only 2x2 pixels large.
I've verified the images are 50x50, but they don't appear to be properly showing.
Here's some of the code going on behind the Thread instance. I'm not entirely sure which code would be beneficial for finding the source for.
public void startThread() {
if (flipWidth != 0 && flipHeight != 0) {
System.out.println("[ AnimationAsset ] " + "We're starting the thread");
Runnable r = new Runnable() {
#Override
public void run() {
runWork();
}
};
animationThread = new Thread(r, "AnimationThread");
animationThread.start();
going = true;
}
}
private void runWork() {
try {
while (going) {
repaint();
flipIndex = (flipIndex + 1) % numFlips;
System.out.println("[ AnimationAsset ] flipIndex: " + flipIndex);
Thread.sleep(1000);
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
System.out.println("[ AnimationAsset ] " + "Interrupted");
}
}
public void paint(Graphics g) {
update(g);
}
public void update(Graphics g) {
System.out.println("[ AnimationAsset ] " + flipIndex);
((Graphics2D) g).drawImage(flipBook.get(flipIndex), null, 5, 5);
}

and adds them to a JPanel
This is not a Swing code. This is AWT code.
You would never override the update() and paint() methods this way when using Swing. Get rid of this code and start over.
To do this in Swing I would use a JLabel with an Icon and add the label to the frame.
Then, to do animation in SWing your should use a Swing Timer.
When the timer fires you simply use the setIcon(...) method of the label to replace the old icon with your new icon.

Emm you have a strange drawing code as
((Graphics2D) g).drawImage(flipBook.get(flipIndex), null, 5, 5);
You can see the docs here... to use Graphic2D drawImage() method right
the most common way of image drawing is to paint image right on JComponent, as a rule, the JLabel. Here is a component example
public class MyLabel extends JLabel
{
private Image image;
public MyLabel(Image image)
{
this.image=image;
}
public void paintComponent(Graphics g)
{
g.drawImage(this.image,x,y,width,height,null);
}
}
so here you can use the component as a common swing object
public class MyPanel extends JPanel
{
public MyPanel()
{
Image image=null;
try{
image=ImageIO.read(new File("image.png"));
}
catch (IOException e) {
}
this.add(new MyLabel(image));
}
}
Good luck