So this is my code:
System.out.println("System Exiting...");
long current = System.currentTimeMillis();
long disired = current + 4000;
boolean done = false;
while (!done)
{
current = System.currentTimeMillis();
if (current == disired)
{
done = true;
System.exit(0);
}
}
My problem is that the print statement doesn't run, well it does run, but it runs at the same time as the exit statement, so you don't see it
[EDIT] Ok, so i just ran this code in its own file(with nothing else), and it works as i want, it prints "system Exiting..." it waits 4 seconds, and the code exits.
so it has to be something to do with the fact that i have this code inside an event listener
Your if condition is much too restrictive since your code will almost never get the times to be exactly equal, but the change needed is very simple:
Change
// hitting this exactly is like finding the proverbial needle
// in the haystack -- almost impossible to do.
if (current == disired)
to
// this is guaranteed to work.
// note if this is in English, you'll want to change disired to desired
if (current >= disired)
Having said this, your while (true) loop is not a good thing to do as it will needlessly tie up the CPU with empty cycles. Instead use some type of event notification or call-back system like ChangeListener or a PropertyChangeListener or a Timer.
You state:
yes it is within a swing GUI
You're calling a long while (true) block of code on the Swing event thread, rendering this thread ineffective. Since the event thread is responsible for all Swing graphics and user interactions, this effectively freezes your GUI until the while loop completes. The solution is obvious: 1) use a Swing Timer for your delay, not a while true loop (this is the callback mechanism that I mentioned in my original answer), and 2) in the future, please give us this important relevant information with the original question since it changes the entire nature of the question.
e.g.
// caveat: code not tested
System.out.println("System Exiting...");
int delay = 4 * 1000;
new Timer(delay, new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
System.out. println("Exited");
System.exit(0);
}
}).start();
e.g.,
import java.awt.Component;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.*;
#SuppressWarnings("serial")
public class TestDelayedExit extends JPanel {
private static final int GAP = 100;
public TestDelayedExit() {
add(new JButton(new DisposeAction("Exit", KeyEvent.VK_X)));
setBorder(BorderFactory.createEmptyBorder(GAP, GAP, GAP, GAP));
}
private static void createAndShowGui() {
JFrame frame = new JFrame("TestDelayedExit");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new TestDelayedExit());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
private class DisposeAction extends AbstractAction {
private int count = 4;
private Timer timer;
public DisposeAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic); // for alt-key combo
}
#Override
public void actionPerformed(ActionEvent e) {
if (timer != null && timer.isRunning()) {
return;
}
final Component c = (Component) e.getSource();
int timerDelay = 1000;
putValue(NAME, String.valueOf(count));
timer = new Timer(timerDelay, new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (count == 0) {
((Timer) e.getSource()).stop();
// this will not work for JMenuItems, and for that
// you would need to get the pop up window's parent component
Window win = SwingUtilities.getWindowAncestor(c);
if (win != null) {
win.dispose();
}
} else {
count--;
putValue(NAME, String.valueOf(count));
}
}
});
timer.start();
}
}
}
Related
Below is the compiled program replica of actual problem code,
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;
public class Dummy {
public static boolean getUserCheck(int size, boolean Check) {
if (Check) {
int ret = JOptionPane.showConfirmDialog(null, size + " entries, Yes or no?",
"Warning", 0);
if (ret > 0) {
System.out.println("User said No: " + ret);
return false;
} else if (ret <= 0) {
System.out.println("user said Yes: " + ret);
return true;
}
}
return true;
}
public static void workerMethod1() {
System.out.println("am worker method 1");
}
public static void workerMethod2() {
System.out.println("am worker method 2");
}
public static void main(String[] args) {
System.out.println("mainthread code line 1");
int size = 13;
boolean thresholdBreach = true;
if (getUserCheck(size, thresholdBreach)) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
workerMethod1();
}
});
SwingUtilities.invokeLater(new Runnable() {
public void run() {
workerMethod2();
}
});
}
System.out.println("mainthread code line 2");
System.out.println("mainthread code line 3");
}
}
where i would like to run the if{} block in main() on separate thread. Because these 2 lines,
System.out.println("mainthread code line 2");
System.out.println("mainthread code line 3");
need not wait for completion of if(){} block
Another problem is, experts recommend to run confirm-dialog methods on event thread.
int ret = JOptionPane.showConfirmDialog(null, size + " entries, Yes or no?",
"Warning", 0);
Please help me!!!!
JOptionPane is a Swing method and should be called on the EDT, the Event Dispatch Thread, and only on this thread, and so it suggests that all your code above should be on the EDT, and that most of your SwingUtilities.invokeLater(new Runnable() calls are completely unnecessary. The only necessary ones will be the main one, where you launch your Swing GUI code, and any areas where Swing calls need to be made from within background threads. Again, if any of the above code is being made within background threads, then the JOptionPane should not be in that thread.
For more specific information in this or any other answer, please provide more specific information in your question. Let's end all confusion. The best way to get us to fully and quickly understand your problem would be if you were to to create and post a minimal example program, a small but complete program that only has necessary code to demonstrate your problem, that we can copy, paste, compile and run without modification.
I have a sneaking suspicion that a decent refactoring along MVC lines could solve most of your problems. Your code is very linear with its lines of code that must follow one another and its if blocks, and it is also tightly coupled with your GUI, two red flags for me. Perhaps better would be less linear code, more event and state-driven code, code where your background code interacts with the GUI via observer notification, and where the background code likewise responds to state changes in the GUI from control notification.
Your control needs two SwingWorkers, one to get the row count and the other to get the rest of the data if the user decides to do so. I'd add a PropertyChangeListener to the first SwingWorker to be notified when the row count data is ready, and then once it is, present it to the view for the user to select whether or not to proceed. If he decides to proceed, I'd then call the 2nd SwingWorker to get the main body of the data.
For example, a rough sketch of what I'm talking about:
import java.awt.Dialog.ModalityType;
import java.awt.Dimension;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutionException;
import javax.swing.*;
#SuppressWarnings("serial")
public class SwingWorkerFooView extends JPanel {
private static final int PREF_W = 400;
private static final int PREF_H = 300;
private JProgressBar progressBar;
private JDialog dialog;
public SwingWorkerFooView() {
add(new JButton(new ButtonAction("Foo", this)));
}
#Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(PREF_W, PREF_H);
}
public boolean showOptionGetAllData(int numberOfRows) {
String message = "Number of rows = " + numberOfRows + ". Get all of the data?";
String title = "Get All Of Data?";
int optionType = JOptionPane.YES_NO_OPTION;
int result = JOptionPane.showConfirmDialog(this, message, title, optionType);
return result == JOptionPane.YES_OPTION;
}
public void showProgressBarDialog() {
progressBar = new JProgressBar();
progressBar.setIndeterminate(true);
Window window = SwingUtilities.getWindowAncestor(this);
dialog = new JDialog(window, "Hang on", ModalityType.APPLICATION_MODAL);
JPanel panel = new JPanel();
panel.add(progressBar);
dialog.add(panel);
dialog.pack();
dialog.setLocationRelativeTo(this);
dialog.setVisible(true);
}
public void closeProgressBarDialog() {
dialog.dispose();
}
private static void createAndShowGui() {
JFrame frame = new JFrame("SwingWorkerFoo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new SwingWorkerFooView());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
#SuppressWarnings("serial")
class ButtonAction extends AbstractAction {
Workers workers = new Workers();
private SwingWorker<Integer, Void> firstWorker;
private SwingWorker<List<String>, Void> secondWorker;
private SwingWorkerFooView mainGui;
public ButtonAction(String name, SwingWorkerFooView mainGui) {
super(name);
this.mainGui = mainGui;
}
#Override
public void actionPerformed(ActionEvent e) {
firstWorker = workers.createFirstWorker();
firstWorker.addPropertyChangeListener(new FirstPropertyChangeListener());
firstWorker.execute();
mainGui.showProgressBarDialog();
}
private class FirstPropertyChangeListener implements PropertyChangeListener {
#Override
public void propertyChange(PropertyChangeEvent evt) {
if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
mainGui.closeProgressBarDialog();
try {
int numberOfRows = firstWorker.get();
boolean getAllData = mainGui.showOptionGetAllData(numberOfRows);
if (getAllData) {
secondWorker = workers.createSecondWorker();
secondWorker.addPropertyChangeListener(new SecondPropertyChangeListener());
secondWorker.execute();
mainGui.showProgressBarDialog();
} else {
// user decided not to get all data
workers.cleanUp();
}
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}
}
private class SecondPropertyChangeListener implements PropertyChangeListener {
#Override
public void propertyChange(PropertyChangeEvent evt) {
if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
mainGui.closeProgressBarDialog();
try {
List<String> finalData = secondWorker.get();
// display finalData in the GUI
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}
}
}
class Workers {
// database object that may be shared by two SwingWorkers
private Object someDataBaseVariable;
private Random random = new Random(); // just for simulation purposes
private class FirstWorker extends SwingWorker<Integer, Void> {
#Override
protected Integer doInBackground() throws Exception {
// The Thread.sleep(...) is not going to be in final production code
// it's just to simulate a long running task
Thread.sleep(4000);
// here we create our database object and check how many rows there are
int rows = random.nextInt(10 + 10); // this is just for demonstration purposes only
// here we create any objects that must be shared by both SwingWorkers
// and they will be saved in a field of Workers
someDataBaseVariable = "Fubar";
return rows;
}
}
private class SecondWorker extends SwingWorker<List<String>, Void> {
#Override
protected List<String> doInBackground() throws Exception {
// The Thread.sleep(...) is not going to be in final production code
// it's just to simulate a long running task
Thread.sleep(4000);
List<String> myList = new ArrayList<>();
// here we go through the database filling the myList collection
return myList;
}
}
public SwingWorker<Integer, Void> createFirstWorker() {
return new FirstWorker();
}
public void cleanUp() {
// TODO clean up any resources and database stuff that will not be used.
}
public SwingWorker<List<String>, Void> createSecondWorker() {
return new SecondWorker();
}
}
The key to all of this is to not to think in a linear console program way but rather to use observer design pattern, i.e., listeners of some sort to check for change of state of both the GUI and the model.
It's essentially:
create worker
add observer to worker (property change listener)
execute worker
show progress bar dialog or notify user in some way that worker is executing.
The listener will be notified when the worker is done, and then you can query the worker (here via the get() method call) as to its end result.
Then the progress dialog can be closed
And the view can display the result or get additional information from the user.
Yes; SwingUtilities.invokeLater() simply places your runnable on the AWT event queue to be processed later, and it is safe to do so at any time.
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.
I have (what should be) a simple problem to tackle and I'm open to other ways to solve it. I am open to other solutions.
The problem:
We are using java swing to display the graphics of a turn-based, tile-based game. I'm using jlabels with icons, absolutely positioned.
To animate the movement, I am using a swing timer that updates the location by 4 pixels at a time, slowly moving the sprite right, left, etc.
To achieve this initially, I was running a timer, which works wonderfully. The problem comes in when I try to move down, then move right.
The sprite moves down, never moves right, and if I watch the execution with some console printing, it's clear to see that both timers are running at the same time. I've done a fair amount of digging on the internet and I wasn't able to find a way to tell a swing timer not to execute until the first timer has stopped, and if I try to busy-wait until one timer finishes (yuck) the UI never displays at all (clearly a step in the wrong direction.)
Now I can convert away from timers altogether and either have the sprite teleport to its new location, or use some awful busy-wait movement scheme, but I'm hoping some kind soul has a solution.
In short: I need a way to run a swing timer for a set period of time, stop it, and then start a new timer, so that they do not overlap. Preferably this method would allow each timer to be in its own method, and I could then call the methods one after the other.
Thanks in advance for any advice you might have.
Edit: Expanded example code. If a full scsse is a requirement for your advice then I'm sorry to have wasted your time, because the full code is a beast. This sample code does not work at all as it stands, sorry, but it should illustrate the point.
So. We have two functions, each with a timer that runs an animation cycle, one for moving down and right diagonally, one for moving straight down.
public class TestClass {
static int counter = 0;
static int counter2 = 0;
static Timer timerC;
static Timer timerX;
public static void main(String[] args) {
moveC();
moveX();
}
public static void moveC() {
int delay = 200; // milliseconds
timerC = new Timer(delay, null);
timerC.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
if (counter < 32) {
counter = counter + 4;
System.out.println("*C*");
} else {
timerC.stop();
System.out.println("*C STOP*");
}
}
});
timerC.start();
}
public static void moveX() {
int delay = 200; // milliseconds
timerX = new Timer(delay, null);
timerX.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
if (counter < 32) {
counter = counter + 4;
System.out.println("*X*");
} else {
timerX.stop();
System.out.println("*X STOP*");
}
}
});
timerX.start();
}
}
What I would want to see here eventually would be
*C*
*C*
*C*
*C*
*C STOP*
*X*
*X*
*X*
*X*
*X STOP*
What I actually get is
*C*
*X*
*C*
*X*
*C*
*X*
*C*
*X*
*C STOP*
*X STOP*
The point I'm trying to get at here is running one animation cycle to completion, then the other.
Thanks again.
Don't use multiple Timers, but rather only one Timer that deals with each direction as it's needed. You need some type of queue to hold the direction information, either a formal queue or a collection that you use as a queue (first in, first out), and then have your Timer extract the direction from this queue as it's running. For example, here I use my JList's model as my queue by removing and using the Direction that was added first (at the top of the JList):
import java.awt.GridLayout;
import java.awt.event.*;
import javax.swing.*;
public class TimerPlay extends JPanel {
private DefaultListModel directionJListModel = new DefaultListModel();
private JList directionJList = new JList(directionJListModel);
JButton startTimerButton = new JButton(
new StartTimerBtnAction("Start Timer"));
public TimerPlay() {
ActionListener directionBtnListener = new ActionListener() {
#Override
public void actionPerformed(ActionEvent actEvt) {
String actionCommand = actEvt.getActionCommand();
Direction dir = Direction.valueOf(actionCommand);
if (dir != null) {
directionJListModel.addElement(dir);
}
}
};
JPanel directionBtnPanel = new JPanel(new GridLayout(0, 1, 0, 10));
for (Direction dir : Direction.values()) {
JButton dirBtn = new JButton(dir.toString());
dirBtn.addActionListener(directionBtnListener);
directionBtnPanel.add(dirBtn);
}
add(directionBtnPanel);
add(new JScrollPane(directionJList));
add(startTimerButton);
}
private class StartTimerBtnAction extends AbstractAction {
protected static final int MAX_COUNT = 20;
public StartTimerBtnAction(String title) {
super(title);
}
#Override
public void actionPerformed(ActionEvent arg0) {
startTimerButton.setEnabled(false);
int delay = 100;
new Timer(delay, new ActionListener() {
private int count = 0;
private Direction dir = null;
#Override
public void actionPerformed(ActionEvent e) {
if (count == MAX_COUNT) {
count = 0; // restart
return;
} else if (count == 0) {
if (directionJListModel.size() == 0) {
((Timer)e.getSource()).stop();
startTimerButton.setEnabled(true);
return;
}
// extract from "queue"
dir = (Direction) directionJListModel.remove(0);
}
System.out.println(dir); // do movement here
count++;
}
}).start();
}
}
private static void createAndShowGui() {
TimerPlay mainPanel = new TimerPlay();
JFrame frame = new JFrame("TimerPlay");
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();
}
});
}
}
enum Direction {
UP, DOWN, LEFT, RIGHT;
}
For reference, this example manages four instances of Timer, two of which run (interleaved) while hovering in any corner. You might compare it to your approach. This related answer discusses animation in a similar tile-based game.
put all Icons in some form of array
create a single Swing Timer with a short delay
in Swing ActionListener, take each `Icon from the array, getBounds from screen, move Icon one step
repeat until target reached.
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.
I was reading different threads on the subject which suggested the Swing Timer class or SwingUtilities.InvokeLater
...but I am having a lot of trouble wrapping my head around them.
I used atomicInteger to create my countdown timer and it works fine in the console. However, When I try to incorporate it in Swing, it only updates the starting and ending value (e.g. set a 5 sec countdown will display in the frame: "5" -> after 5 seconds -> "0".
Is there any simple way for me to keep and "refresh" my atomicInteger countdown label, or the only way is using the Swing Timer class?
Thank you for your patience!
ps. not homework, just trying to make myself a custom timer to study. (ie. procrastinating)
I hope this class is enough, please let me know if you need the frame/panel code as well.
private class ClickListener implements ActionListener{
public void actionPerformed(ActionEvent e){
int t_study = 5;
atomicDown.set(t_study);
if (e.getSource() == b_study){
while(atomicDown.get() > 0){
t_study = atomicDown.decrementAndGet();
l_studyTime.setText(Integer.toString(t_study));
try {
Thread.sleep(1000);
}
catch (InterruptedException e1) {
System.out.println("ERROR: Thread.sleep()");
e1.printStackTrace();
}
}
}
else if(e.getSource() == b_exit){
System.exit(0);
}
else
System.out.println("ERROR: button troll");
}
}
After turning the code snippet into an SSCCE, this is what I get (which seems to work - as best as I understand the original code).
I have not changed the variable names. Please learn common Java naming conventions1 for class, method & attribute names & use it consistently.
Specifically names like b_study should be more along the lines of studyButton or similar. Some will note that 'button' should not be part of the name, but when you have a GUI with both a 'Study' button & label, I don't see any other logical way to separate them.
import java.awt.event.*;
import javax.swing.*;
import java.util.concurrent.atomic.AtomicInteger;
class TimerTicker {
public static final int STUDY_TIME = 15;
AtomicInteger atomicDown = new AtomicInteger(STUDY_TIME);
JButton b_study;
JButton b_exit;
JLabel l_studyTime;
TimerTicker() {
JPanel gui = new JPanel();
b_study = new JButton("Study");
ClickListener listener = new ClickListener();
b_study.addActionListener(listener);
gui.add(b_study);
b_exit = new JButton("Exit");
b_exit.addActionListener(listener);
gui.add(b_exit);
l_studyTime = new JLabel("" + atomicDown.get());
gui.add(l_studyTime);
JOptionPane.showMessageDialog(null, gui);
}
private class ClickListener implements ActionListener {
Timer timer;
public void actionPerformed(ActionEvent e){
if (e.getSource() == b_study) {
ActionListener countDown = new ActionListener() {
public void actionPerformed(ActionEvent ae) {
if (!(atomicDown.get() > 0)) {
timer.stop();
// reset the count.
atomicDown.set(STUDY_TIME);
} else {
l_studyTime.setText(
Integer.toString(
atomicDown.decrementAndGet()));
}
}
};
timer = new Timer(1000,countDown);
timer.start();
} else if(e.getSource() == b_exit) {
System.exit(0);
} else {
System.out.println("ERROR: button troll");
}
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new TimerTicker();
}
});
}
}