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JLabel Overlapping Text in GUI

I'm trying to make a clock using as few resources as possible and just relying on my (limited) knowledge of Java. I've come to a road block however. The clock I wrote works, except rather than the text in the jlabel being replaced, it overlaps itself. I've tried fixing this by clearing the value of timeStamp, but it doesn't seem to be working.
public class Clock extends JFrame{
public static void main (String args[]) {
Clock gui = new Clock();
gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
gui.setSize(50,50);
gui.setVisible(true);
gui.setTitle("Clock");
int a = 1;
while (a == 1){
String timeStamp = new SimpleDateFormat("hh:mm:ss a").format(Calendar.getInstance().getTime());
JLabel label;
label = new JLabel();
label.setText(String.valueOf(timeStamp));
timeStamp = "";
gui.add(label);
label.revalidate();
}
}
}

You should not be creating a new JLabel every iteration.
JLabel label = new JLabel();
gui.add(label);
while (a == 1){
String timeStamp = new SimpleDateFormat("hh:mm:ss a").format(Calendar.getInstance().getTime());
label.setText(String.valueOf(timeStamp));
timeStamp = "";
label.revalidate();
}

You should use a SwingWorker to update the clock. Currently you're doing it on the event dispatch thread and thus interfere with the UI rendering.
Besides that you should reuse the label instead of creating a new one for each timestamp. Currently you're stacking labels on top of each other since gui.add() will just add the new label and won't remove the old ones.

Why are you creating a new JLabel in every iteration of the loop?
Don't do that.
Just create a single label in Clock's constructor.
Also, changing the label's text should be done on the event thread, not the main thread.

While the code you wrote "works", you're missing some things to make a stable Swing GUI.
You must always start a Swing application using the SwingUtilities invokelater method. This puts the creation and the execution of the Swing components on the Event Dispatch thread (EDT).
I separated the creation of the GUI from the execution of the GUI. Separation of concerns makes coding each part easier.
In the Timer Runnable, I again use the SwingUtilities invokeLater method to make sure that the updating of the JTextField with the time happens on the EDT.
I stop the Thread before I exit. Generally, you should stop any threads you start, and not rely on the JVM to clean up for you.
Here's the clock.
And here's the code.
package com.ggl.testing;
import java.awt.Color;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class SimpleClock implements Runnable {
private JFrame frame;
private JPanel panel;
private JTextField clockDisplay;
private Timer timer;
#Override
public void run() {
frame = new JFrame("Clock");
frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
frame.addWindowListener(new WindowAdapter() {
#Override
public void windowClosing(WindowEvent event) {
exitProcedure();
}
});
panel = new JPanel();
panel.setBorder(BorderFactory.createLineBorder(Color.BLACK, 6));
clockDisplay = new JTextField(12);
clockDisplay.setEditable(false);
clockDisplay.setHorizontalAlignment(JTextField.CENTER);
panel.add(clockDisplay);
frame.add(panel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
timer = new Timer(this);
new Thread(timer).start();
}
public void exitProcedure() {
timer.setRunning(false);
frame.dispose();
System.exit(0);
}
public void setText(String text) {
clockDisplay.setText(text);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Clock());
}
public class Timer implements Runnable {
private volatile boolean running;
private SimpleClock clock;
private SimpleDateFormat timeFormat;
public Timer(SimpleClock clock) {
this.clock = clock;
this.running = true;
this.timeFormat = new SimpleDateFormat("h:mm:ss a");
}
#Override
public void run() {
while (running) {
displayTime();
sleep();
}
}
public void displayTime() {
final Calendar calendar = Calendar.getInstance();
Date date = calendar.getTime();
final String s = timeFormat.format(date);
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
clock.setText(s);
}
});
}
public void sleep() {
try {
Thread.sleep(200L);
} catch (InterruptedException e) {
}
}
public synchronized void setRunning(boolean running) {
this.running = running;
}
}
}

find how long swing timer has been running

I'm making a stop watch and I know how to do everything, except find how long my timer object has been going. Is there a method like timer.getElapsedTime() or something of that nature?
Edit: There are numbers saying 00 00 00. Every second it needs to increment. My thought process is seconds = timer.getElapsedTime();
secs.setText(seconds)

Just save System.currentTimeMillis() in some variable when you set your timer, and compare the value to the current return value when you need the elapsed time.
EDIT: Make the timer fire once every second. Note that we re-set the timer every time it fires to prevent lag and processing time from accumulating.
package timertest;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.Timer;
public class TimerTest implements ActionListener {
JLabel timeDisplay;
long startTime;
Timer timer;
int seconds;
public void createAndShowGUI() {
JFrame frame=new JFrame("Stopwatch");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
timeDisplay=new JLabel("0");
frame.getContentPane().add(timeDisplay);
frame.pack();
frame.setVisible(true);
startTime=System.currentTimeMillis();
seconds=1;
timer=new Timer(1000, this);
timer.setRepeats(false);
timer.start();
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
new TimerTest().createAndShowGUI();
}
});
}
#Override
public void actionPerformed(ActionEvent e) {
long now=System.currentTimeMillis();
long elapsed=now-startTime;
seconds++;
timeDisplay.setText(elapsed+" Milliseconds since start");
timer.setInitialDelay((int)(startTime+seconds*1000-now));
timer.start();
}
}

You can make your own timer class. (Or inherit from the current timer class and add this functionality)
public class Timer
{
private long startTime = 0;
public void start()
{
startTime = System.currentTimeMillis();
}
public int getElapsedTime()
{
return (System.currentTimeMillis() - startTime) / 1000 //returns in seconds
}
}

Counting and printing time in java using swing

I'm trying to implement a timer using one thread and print it on a JButton using another thread.
my class for time is like this:
public class Time extends Thread
{
int counter = 0;
public String currentTime = new String();
public String printFormat(int second)
{
return String.format("%d:%d", second/60, second%60);
}
synchronized public void count(int minute) throws InterruptedException
{
minute *= 60;
while(minute >= 0)
{
wait(1000);
minute--;
currentTime = printFormat(minute);
System.out.println(currentTime);
}
}
and my main thread is like this:
button.setText(time.currentTime);
what is wrong with this piece of code?

"if you can explain it using java swing timer , I would appreciate that"
If you want to use a javax.swing.Timer do the following, it really simple.
The same way you set a ActionListener to a button, you do the same for the timer. Except instead of the button firing the event, it's fired by the timer, every duration period you set for it.
In the case of a clock like timer, you would set it to 1000,
indication do something every 1000 milliseconds.
In this particular
example, I just set the text of the button with a count value that I
increment by one every time the timer event is fired. Heres the Timer code
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
button.setText(String.valueOf(count));
count++;
}
});
timer.start();
As you can see it' pretty simple
You can run this example
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class ButtonTimer {
private JButton button = new JButton(" ");
private int count = 1;
public ButtonTimer() {
Timer timer = new Timer(1000, new ActionListener(){
public void actionPerformed(ActionEvent e) {
button.setText(String.valueOf(count));
count++;
}
});
timer.start();
JFrame frame = new JFrame();
frame.add(button);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new ButtonTimer();
}
});
}
}
If you want help trying to figure out your current code, consider posting a runnable program we can test out. So we can see where you're going wrong.
Here's a tutorial on Concurrency With Swing

Stop a loop in java with graphical interface (buttons)

I created a graphic interface in java and 2 buttons.
My aim :
1) When I click on the first button, having a loop in which different tasks are processed (Button "Start"). Between each loop there is a stop of 10 seconds
2) When I click on the second button, the loop is processed immediately one last time but then stopped.
(I also would like to make a pop up showing that it has been stopped but that's not the main question, I think I can do it.)
I tried the following code, but first I think they are more simple ways to sort my problem. Plus I can compile but it doesn't work, the loop is not stopped, the window crashes:
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
globalStop="Run";
while (globalStop.equals("Run")) {
System.out.println("GO");
// Other stuff
// For the break ?
try {
Thread.sleep(10000);
} catch (InterruptedException ex) {
Logger.getLogger(main.class.getName()).log(Level.SEVERE, null, ex);
}
}
System.out.println("done");
}
}
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
globalStop = "Stop";
System.out.println("Bouton2");
}
I hope I was clear enough, if that is not the case, please let me know and I will rephrase.
Thank you all in advance for your help.

I wondered how long it would take me to create a United States type traffic signal GUI. It took 75 minutes. I was able to create the GUI quickly because a lot of Swing is boilerplate. Once you create one GUI, you can copy some of the classes for your next GUI.
Here's an image of the traffic signal GUI.
When you press the Start button, the traffic signal will cycle from green to yellow to red. The traffic signal will cycle forever, until you press the Stop button.
When you press the Stop button, the traffic signal will turn red. It will stay red forever, until you press the Start button.
When you press the Start button while the traffic signal is cycling, the green to yellow to red cycle starts over.
Basically, the following steps show you how to create any Swing GUI. I didn't create the code in this order, but it makes sense to explain the code in a logical order. So, let's dig into the code.
This is the model class for the GUI. Every GUI needs to have it's own model, separate from the model of the application. For this GUI, the model is simple.
package com.ggl.traffic.signal.model;
import java.awt.Dimension;
public class TrafficSignalModel {
public static final int RED_LIGHT_TIME = 15;
public static final int YELLOW_LIGHT_TIME = 5;
public static final int GREEN_LIGHT_TIME = 10;
public static final Dimension LIGHT_SIZE = new Dimension(32, 32);
}
We set the signal light times in the model, as well as the size of the traffic lights.
For a more complicated GUI, we would keep track of the field values in the model.
Next, we have the main class of the traffic signal GUI.
package com.ggl.traffic.signal;
import javax.swing.SwingUtilities;
import com.ggl.traffic.signal.view.TrafficSignalFrame;
public class TrafficSignal implements Runnable {
#Override
public void run() {
new TrafficSignalFrame();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new TrafficSignal());
}
}
This class ensures that the traffic signal GUI is on the Swing event thread. That's all this class does. You can see how you can copy this class to start any GUI.
Next, we have the Frame class of the GUI.
package com.ggl.traffic.signal.view;
import java.awt.FlowLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
public class TrafficSignalFrame {
protected ButtonPanel bPanel;
protected JFrame frame;
protected TrafficSignalPanel tsPanel;
public TrafficSignalFrame() {
createPartControl();
}
protected void createPartControl() {
tsPanel = new TrafficSignalPanel();
bPanel = new ButtonPanel();
bPanel.setTrafficSignalPanel(tsPanel);
frame = new JFrame();
frame.setTitle("Traffic Signal");
frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
frame.addWindowListener(new WindowAdapter() {
#Override
public void windowClosing(WindowEvent event) {
exitProcedure();
}
});
frame.setLayout(new FlowLayout());
frame.add(bPanel.getPanel());
frame.add(tsPanel.getPanel());
frame.pack();
// frame.setBounds(100, 100, 400, 200);
frame.setVisible(true);
}
public void exitProcedure() {
frame.dispose();
System.exit(0);
}
public JFrame getFrame() {
return frame;
}
}
This class is boilerplate, except for the particular JPanels that will make up the GUI. If your JFrame has a JMenu, this would be the place to attach your JMenu to your JFrame.
Notice that I did not extend JFrame to make this class. The only time you extend a Swing component is when you're overriding one or more of the component's methods. If I need the actual JFrame, I call the getFrame() method. Using Swing components rather than extending Swing components keeps my methods separate from the Swing methods.
Next, we'll look at the traffic signal light panel. This panel makes up one of the 3 lights in the traffic signal.
package com.ggl.traffic.signal.view;
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;
public class TrafficSignalLightPanel extends JPanel {
private static final long serialVersionUID = 1L;
protected boolean lightOn;
protected Color lightColor;
protected Color darkColor;
public TrafficSignalLightPanel(Color lightColor) {
this.lightColor = lightColor;
this.darkColor = Color.WHITE;
this.lightOn = false;
}
public void setLightOn(boolean lightOn) {
this.lightOn = lightOn;
this.repaint();
}
#Override
public void paintComponent(Graphics g) {
if (lightOn) {
g.setColor(lightColor);
} else {
g.setColor(darkColor);
}
g.fillRect(0, 0, getWidth(), getHeight());
}
}
This class extends JPanel, because we want to override the paintComponent method. This is a simple class. All it does is paint the panel a color, or white.
Next, we'll look at the traffic signal panel. This panel creates 3 light panels and arranges them in a vertical row.
package com.ggl.traffic.signal.view;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import javax.swing.BorderFactory;
import javax.swing.JPanel;
import javax.swing.border.Border;
import com.ggl.traffic.signal.model.TrafficSignalModel;
public class TrafficSignalPanel {
protected JPanel panel;
protected TrafficSignalLightPanel redLight;
protected TrafficSignalLightPanel yellowLight;
protected TrafficSignalLightPanel greenLight;
public TrafficSignalPanel() {
createPartControl();
}
protected void createPartControl() {
Border border = BorderFactory.createLineBorder(Color.BLACK, 4);
redLight = new TrafficSignalLightPanel(Color.RED);
redLight.setBorder(border);
redLight.setPreferredSize(TrafficSignalModel.LIGHT_SIZE);
yellowLight = new TrafficSignalLightPanel(Color.YELLOW);
yellowLight.setBorder(border);
yellowLight.setPreferredSize(TrafficSignalModel.LIGHT_SIZE);
greenLight = new TrafficSignalLightPanel(Color.GREEN);
greenLight.setBorder(border);
greenLight.setPreferredSize(TrafficSignalModel.LIGHT_SIZE);
panel = new JPanel();
panel.setLayout(new FlowLayout());
panel.setPreferredSize(
new Dimension(TrafficSignalModel.LIGHT_SIZE.width + 10,
TrafficSignalModel.LIGHT_SIZE.height * 3 + 25));
panel.add(redLight);
panel.add(yellowLight);
panel.add(greenLight);
}
public JPanel getPanel() {
return panel;
}
public TrafficSignalLightPanel getRedLight() {
return redLight;
}
public TrafficSignalLightPanel getYellowLight() {
return yellowLight;
}
public TrafficSignalLightPanel getGreenLight() {
return greenLight;
}
}
A fairly straightforward creation of a JPanel from 3 JPanels. I set the preferred size of the JPanel so the lights will be in a vertical row.
Next, we'll look at the button panel. You can pretty much copy this code into any GUI that has a button panel.
package com.ggl.traffic.signal.view;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JPanel;
import com.ggl.traffic.signal.thread.TrafficSignalCycle;
public class ButtonPanel {
protected JButton startButton;
protected JButton stopButton;
protected JPanel panel;
protected TrafficSignalCycle thread;
protected TrafficSignalPanel tsPanel;
public ButtonPanel() {
this.thread = null;
createPartControl();
}
protected void createPartControl() {
panel = new JPanel();
panel.setLayout(new FlowLayout());
startButton = new JButton("Start");
startButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent event) {
if (thread != null) {
thread.stopRunning();
}
tsPanel.getRedLight().setLightOn(false);
tsPanel.getYellowLight().setLightOn(false);
tsPanel.getGreenLight().setLightOn(false);
thread = new TrafficSignalCycle(tsPanel);
thread.start();
}
});
panel.add(startButton);
stopButton = new JButton("Stop");
stopButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent event) {
if (thread != null) {
thread.stopRunning();
thread = null;
}
tsPanel.getRedLight().setLightOn(true);
tsPanel.getYellowLight().setLightOn(false);
tsPanel.getGreenLight().setLightOn(false);
}
});
panel.add(stopButton);
setButtonSizes(startButton, stopButton);
}
protected void setButtonSizes(JButton ... buttons) {
Dimension preferredSize = new Dimension();
for (JButton button : buttons) {
Dimension d = button.getPreferredSize();
preferredSize = setLarger(preferredSize, d);
}
for (JButton button : buttons) {
button.setPreferredSize(preferredSize);
}
}
protected Dimension setLarger(Dimension a, Dimension b) {
Dimension d = new Dimension();
d.height = Math.max(a.height, b.height);
d.width = Math.max(a.width, b.width);
return d;
}
public void setTrafficSignalPanel(TrafficSignalPanel tsPanel) {
this.tsPanel = tsPanel;
}
public JPanel getPanel() {
return panel;
}
}
The button actions were simple enough that I could keep them in the button panel. If you want, you can code separate action classes.
Finally, here's the code that runs the traffic light cycle. It's an extension of the Thread class, so it can be run in a separate thread from the GUI. It's always a good idea to do work in threads separate from the GUI thread.
package com.ggl.traffic.signal.thread;
import javax.swing.SwingUtilities;
import com.ggl.traffic.signal.model.TrafficSignalModel;
import com.ggl.traffic.signal.view.TrafficSignalLightPanel;
import com.ggl.traffic.signal.view.TrafficSignalPanel;
public class TrafficSignalCycle extends Thread {
protected boolean isRunning;
protected boolean isFinished;
protected TrafficSignalPanel tsPanel;
public TrafficSignalCycle(TrafficSignalPanel tsPanel) {
this.tsPanel = tsPanel;
this.isRunning = true;
this.isFinished = false;
}
#Override
public void run() {
while (isRunning) {
signalLightOn(tsPanel.getGreenLight(), TrafficSignalModel.GREEN_LIGHT_TIME);
signalLightOn(tsPanel.getYellowLight(), TrafficSignalModel.YELLOW_LIGHT_TIME);
signalLightOn(tsPanel.getRedLight(), TrafficSignalModel.RED_LIGHT_TIME);
}
this.isFinished = true;
}
protected void signalLightOn(TrafficSignalLightPanel light, int seconds) {
if (isRunning) {
setLightOn(light, true);
}
for (int i = 0; i < 1000 && isRunning; i++) {
try {
Thread.sleep(1L * seconds);
} catch (InterruptedException e) {
}
}
setLightOn(light, false);
}
protected void setLightOn(final TrafficSignalLightPanel light,
final boolean isLightOn) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
light.setLightOn(isLightOn);
}
});
}
public void stopRunning() {
this.isRunning = false;
while (!isFinished) {
try {
Thread.sleep(10L);
} catch (InterruptedException e) {
}
}
}
}
The method that actually changes the color of the signal light must execute in the Swing event thread. That's what the setLightOn method does by calling SwingUtilities.
The timing loop is a bit complicated because we want to be able to stop the thread in a few milliseconds. The isFinished boolean ensures that the thread is stopped completely, so that the lights can be set.
This is a fairly long answer, but I hope it's helpful to anyone creating a Swing GUI.

You shouldn't be looping within the UI thread, nor telling it to sleep. Fundamentally you should keep the UI thread as free as possible.
If you need something to occur on a regular basis in a Swing UI in the UI thread, use a Swing Timer.
It's unclear what you're doing in the "other stuff" however - it's possible that you should be doing that in a different thread entirely and using (say) an AtomicBoolean to indicate when you want to stop.

1. You should always keep the UI thread for UI work and Non-UI thread for Non-UI work.
2. In Java GUI, the main() is not Long lived, after assigning the construction of GUI to the Event Dispatcher Thread, the main() quits, and now its EDT's responsibility handle the GUI.
3. So when you click the buttons, and the work you are doing is doing some heavy process or its time consuming....then span a Separate thread.
4. You can use Thread or SwingWorker.
Example:
Button b = new Button("Click me");
b.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
Thread t = new Thread(new Runnable(){
public void run(){
// Do the Heavy Processing work.....
}
});
t.start();
}
});

The easy but dirty way:
Multi-thread your program and have one thread do your loop and a second thread monitor your buttons. Have the button change your globalStop variable
The not so easy but cleaner way:
Make the button throw an interrupt to change the value. After the interrupt the for loop will continue to the end.

Java Swing: How do I wake up the main thread from the event-dispatch thread?

I want to cause the "main thread" (the thread started which runs main()) to do some work from the actionPerformed() method of a button's ActionListener, but I do not know how to achieve this.
A little more context:
I am currently programming a 2D game using Swing (a flavour of Tetris).
When the application starts, a window opens which displays the main menu of the game.
The user is presented several possibilities, one of them is to start the game by pushing a "Start" button, which causes the game panel to be displayed and triggers the main loop of the game.
To be able to switch between the two panels (that of the main menu and that of the game), I am using a CardLayout manager, then I can display one panel by calling show().
The idea is that I would like my start button to have a listener that looks like this:
public class StartListener implements ActionListener {
StartListener() {}
public void actionPerformed(ActionEvent e) {
displayGamePanel();
startGame();
}
}
but this does not work because actionPerformed() is called from the event-dispatch thread, so the call to startGame() (which triggers the main loop: game logic update + repaint() call at each frame) blocks the whole thread.
The way I am handling this right now is that actionPerformed() just changes a boolean flag value: public void actionPerformed(ActionEvent e) {
startPushed = true;
}
which is then eventually checked by the main thread:
while (true) {
while (!g.startPushed) {
try {
Thread.sleep(100);
} catch (Exception e) {}
}
g.startPushed = false;
g.startGame();
}
But I find this solution to be very inelegant.
I have read the Concurrency in Swing lesson but I am still confused (should I implement a Worker Thread – isn't that a little overkill?). I haven't done any actual multithreading work yet so I am a little lost.
Isn't there a way to tell the main thread (which would be sleeping indefinitely, waiting for a user action) "ok, wake up now and do this (display the game panel and start the game)"?.
Thanks for your help.
EDIT:
Just to be clear, this is what my game loop looks like:
long lastLoopTime = System.currentTimeMillis();
long dTime;
int delay = 10;
while (running) {
// compute the time that has gone since the last frame
dTime = System.currentTimeMillis() - lastLoopTime;
lastLoopTime = System.currentTimeMillis();
// UPDATE STATE
updateState(dTime);
//...
// UPDATE GRAPHICS
// thread-safe: repaint() will run on the EDT
frame.repaint()
// Pause for a bit
try {
Thread.sleep(delay);
} catch (Exception e) {}
}

This doesn't make sense:
but this does not work because actionPerformed() is called from the event-dispatch thread, so the call to startGame() (which triggers the main loop: game logic update + repaint() call at each frame) blocks the whole thread.
Since your game loop should not block the EDT. Are you using a Swing Timer or a background thread for your game loop? If not, do so.
Regarding:
while (true) {
while (!g.startPushed) {
try {
Thread.sleep(100);
} catch (Exception e) {}
}
g.startPushed = false;
g.startGame();
}
Don't do this either, but instead use listeners for this sort of thing.
e.g.,
import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class GameState extends JPanel {
private CardLayout cardlayout = new CardLayout();
private GamePanel gamePanel = new GamePanel();
private StartPanel startpanel = new StartPanel(this, gamePanel);
public GameState() {
setLayout(cardlayout);
add(startpanel, StartPanel.DISPLAY_STRING);
add(gamePanel, GamePanel.DISPLAY_STRING);
}
public void showComponent(String displayString) {
cardlayout.show(this, displayString);
}
private static void createAndShowGui() {
GameState mainPanel = new GameState();
JFrame frame = new JFrame("GameState");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class StartPanel extends JPanel {
public static final String DISPLAY_STRING = "Start Panel";
public StartPanel(final GameState gameState, final GamePanel gamePanel) {
add(new JButton(new AbstractAction("Start") {
#Override
public void actionPerformed(ActionEvent e) {
gameState.showComponent(GamePanel.DISPLAY_STRING);
gamePanel.startAnimation();
}
}));
}
}
class GamePanel extends JPanel {
public static final String DISPLAY_STRING = "Game Panel";
private static final int PREF_W = 500;
private static final int PREF_H = 400;
private static final int RECT_WIDTH = 10;
private int x;
private int y;
public void startAnimation() {
x = 0;
y = 0;
int timerDelay = 10;
new Timer(timerDelay , new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
x++;
y++;
repaint();
}
}).start();
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.fillRect(x, y, RECT_WIDTH, RECT_WIDTH);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
}

you should be using a SwingWorker this will execute the code in doInBackground() in a background thread and the code in done() in the EDT after doInBackground() stops

The easiest way: use a CountDownLatch. You set it to 1, make it available in the Swing code by any means appropriate, and in the main thread you await it.

You can consider showing a modal dialog with the game panel using SwingUtilities.invokeAndWait() so that when the dialog is closed the control returns back to main thread.

You can make all code except the EDT run on single thread execution service and then just post runnables whenever you need some code executed.