I am trying to control a while loop in my program to stop and start based on a user input. I have attempted this with a button and the "start" part of it works but then the code goes into an infinite loop which I cant stop without manually terminating it. The following is all my code:
Header Class
package test;
import javax.swing.JFrame;
public class headerClass {
public static void main (String[] args){
frameClass frame = new frameClass();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(150,75);
frame.setVisible(true);
}
}
Frame Class
package test;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class frameClass extends JFrame {
private JButton click;
public frameClass(){
setLayout(new FlowLayout());
click = new JButton("Stop Loop");
add(click);
thehandler handler = new thehandler();
click.addActionListener(handler);
}
private class thehandler implements ActionListener{
public void actionPerformed(ActionEvent e){
if(e.getSource()==click){
looper loop = new looper();
looper.buttonSet = !looper.buttonSet;
}
}
}
}
Looping class
package test;
public class looper {
public static boolean buttonSet;
public looper(){
while (buttonSet==false){
System.out.println("aaa");
}
}
}
How do I fix this and stop if from going into the infinite loop please?
Swing is a single threaded framework, this means that while the loop is running, the Event Dispatching Thread is been blocked and can't process new events, including repaint requests...
You need to start your Looper class inside it's own thread context. This would also mean that your loop flag would need to be declared volatile or you should use an AtomicBoolean so that state can be inspected and modified across thread boundaries
For example...
public class Looper implements Runnable {
private AtomicBoolean keepRunning;
public Looper() {
keepRunning = new AtomicBoolean(true);
}
public void stop() {
keepRunning.set(false);
}
#Override
public void run() {
while (keepRunning.get()) {
System.out.println("aaa");
}
}
}
Then you might be able to use something like...
private class thehandler implements ActionListener {
private Looper looper;
public void actionPerformed(ActionEvent e) {
if (e.getSource() == click) {
if (looper == null) {
looper = new Looper();
Thread t = new Thread(looper);
t.start();
} else {
looper.stop();
looper = null;
}
}
}
}
to run it...
Take a look at Concurrency in Swing and Concurrency in Java for some more details
Also beware, Swing is not thread safe, you should never create or modify the UI from out side the context of the EDT
The problem is you start an infinite loop and try to terminate it in the same thread. That doesn't work because the VM executes one task in a thread after another. It would execute the command to stop the looper directly after the loop is finished but an infinite loop never finishes. So it cannot be stopped like this.
You need to create a second Thread for the looper. This way you can stop it from your main thread.
Related
I understand that Swing GUIs themselves use Threads, but I am trying to use a separate thread to run my simulation. I created a class that implements Runnable and uses a custom Thread as most simple Runnable examples do. My run() method basically runs my simulation, updating every second (which works great), but I'm now trying to implement buttons that can pause/resume the simulation. My Start button successfully starts the thread, and my Pause button successfully pauses the thread. However, when Pause is selected, the entire GUI is paused, and you can see the button as still being selected and I am unable to select any buttons or interact with the GUI at all. As soon as I call wait() on my custom thread, my entire GUI halts, even though I'm using a Thread separate from this GUI. Why does calling wait() freeze up my GUI? How can I pause just this specific Thread and not the entire GUI?
Please note that the Start button should be what makes the program resume. Here's my code for the GUI:
import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class GridFrame extends JFrame {
private static final long serialVersionUID = 2857470112009359285L;
private MyGridPanel grid;
private Simulation sim;
GridFrame(Simulation sim, int w, int h, int rows, int cols) {
this.sim = sim;
setTitle("Simulation");
setSize(w, h);
grid = new MyGridPanel(w, h, rows, cols);
add(grid, BorderLayout.CENTER);
//Build bottom panel
JPanel buttons = new JPanel();
buttons.setLayout(new GridLayout(1,3));
JButton start = new JButton("Start");
JButton pause = new JButton("Pause");
JButton reset = new JButton("Reset");
start.setActionCommand("Start");
start.addActionListener(new ButtonActionListener());
pause.setActionCommand("Pause");
pause.addActionListener(new ButtonActionListener());
reset.setActionCommand("Reset");
reset.addActionListener(new ButtonActionListener());
buttons.add(start);
buttons.add(pause);
buttons.add(reset);
add(buttons, BorderLayout.SOUTH);
}
public MyGridPanel getGrid(){
return grid;
}
private class ButtonActionListener implements ActionListener{
#Override
public void actionPerformed(ActionEvent e) {
switch(e.getActionCommand()){
case "Start":
System.out.println("Start");
sim.start();
break;
case "Pause":
System.out.println("Pause");
sim.pause();
break;
case "Reset":
System.out.println("Reset");
break;
}
}
}
}
And here is my Runnable:
public class Simulation implements Runnable{
private Thread t;
private GridFrame frame;
private boolean paused;
public Simulation(){
frame = new GridFrame(this, 300, 300, 10, 10);
frame.setVisible(true);
paused = true;
}
public void start () {
if(t == null){
//Thread has not been created. Simulation has not started to run yet
System.out.println("Starting thread.");
t = new Thread(this);
t.start();
paused = false;
}
else if(paused){
//Simulation and thread already started to run but was paused. This should use notify() to resume the thread.
resume();
paused = false;
}
}
public void resume(){
synchronized(t){
t.notify();
}
}
public void pause(){
synchronized(t){
try {
t.wait();
paused = true;
} catch (InterruptedException e) {
System.out.println("Exception when trying to pause simulation");
e.printStackTrace();
}
}
}
#Override
public void run() {
while(true){
frame.getGrid().step();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
System.out.println("Thread interrupted while simulation was running.");
e.printStackTrace();
}
}
}
public static void main(String[] a) {
Simulation s = new Simulation();
}
}
Calling wait and notify on a Thread object behaves no differently than it does on any other object. Specifically, as you've noticed, it does not send a signal to the executing thread that it should pause, but rather it will block the calling thread (your UI thread in this case) until it receives a notify message.
You will need to implement a messaging system (such as a blocking queue) from your UI thread to your background thread in order to get what you want.
Here is my example code:
package javaapplication35;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.logging.Level;
import java.util.logging.Logger;
import static javaapplication35.ProgressBarExample.customProgressBar;
import javax.swing.JButton;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;
public class ProgressBarExample {
final static JButton myButton =new JButton("Start");
final static JProgressBar customProgressBar = new JProgressBar();
private static final JPanel myPanel = new JPanel();
public static void main(String[] args) {
customProgressBar.setMaximum(32);
customProgressBar.setStringPainted(true);
myPanel.add(customProgressBar);
myPanel.add(myButton);
myButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e)
{
Thread firstly =new Thread(new Runnable (
) {
#Override
public void run() {
Calculations a = new Calculations();
a.doCaculations();
}
});
Thread secondly =new Thread(new Runnable (
) {
#Override
public void run() {
JOptionPane.showMessageDialog(null,"just finished");
}
});
firstly.start();
try {
firstly.join();
} catch (InterruptedException ex) {
Logger.getLogger(ProgressBarExample.class.getName()).log(Level.SEVERE, null, ex);
}
secondly.start();
}
});
JOptionPane.showMessageDialog(null, myPanel, "Progress bar test", JOptionPane.PLAIN_MESSAGE);
}
}
class Calculations {
public void doCaculations() {
new SwingWorker<Void, Void>() {
#Override
protected Void doInBackground() throws Exception {
int value = 0;
while (value < customProgressBar.getMaximum()) {
Thread.sleep(250);
value ++;
customProgressBar.setValue(value);
}
return null;
}
}.execute();
}
private void doOtherStaff(){
//more methods, that don't need to run in seperate threads, exist
}
}
There are 2 Threads.
The firstly thread creates a Calculations class insance and then runs a doCaculations() method on it.
The secondly thread pops-up a message.
The doCaculations() method in my "real" code performs some time consuming maths and in order to simulate the time spent I added that Thread.sleep(250);. I need to inform the user on the progress of the calculations so I am using the progressbar, that is updated by the doCaculations() method.
I am trying to make the code work in a way that the secondly thread runs after the firstly thread finishes. But I cannot make it work. What happens is that the pop-up message pops-up immediately (and that means that it's thread run before I want it to run).
Note:The "just finished" message is there just to test the code. In my "real" program a method would be in it's place. I am making this note because if I just wanted a message to show I could just place it in the end of the doCaculations() method, and everything would work fine.
I know I must be doing wrong with the Thread handling but I cannot find it. Any ideas?
PS: A thought: Actually the doCaculations() method has its own thread. So it runs "in a SwingWorker inside a Thread". Iguess the firstly.join(); works correctly. But after the doCaculations() method is called the fistrly thread is considered finished, and that's why the code goes on with the secondly thread, not knowing that the doCaculations() thread is still doing something.
In java you can use swingworker and in the done() method call your Dialog
In android you can use AsyncTask for calling the new thread and in the OnPostExecute method, call show message dialog.
Try
a.doCaculations();
a.join();
edit:
Since you are using SwingWorker my previous answer is incorrect, but, as in you comment, you've extended Thread, the following should work for you:
Thread a = new Calculations();
a.start();
a.join();
Don't forget, that you have to override run method in Calculations class, like:
class Calculations extends Thread {
#Override
public void run() {
//your code here
}
}
Your Calculations class must extend SwingWorker. You do your calculations in doInBackground()
public class Calculations extends SwingWorker<Void, Void>{
#Override
protected Void doInBackground() throws Exception {
System.out.println("Calculating.");
Thread.sleep(3000);
return null;
}
}
And in your actionPerformed() you use Calculations like this.
public void actionPerformed(ActionEvent e)
{
//FISRT run method
Calculations a = new Calculations();
a.execute(); // Start calculations
try {
a.get(); // Wait for calculations to finish
} catch (InterruptedException | ExecutionException e1) {
e1.printStackTrace();
}
//THEN inform that just finished
JOptionPane.showMessageDialog(null,"just finished");
}
EDIT: If you have multiple methods that you would like to run in a SwingWorker you can keep your code almost like it is. But only add these lines.
public class Calculations{
protected void calculate() {
SwingWorker sw = new SwingWorker(){
#Override
protected Object doInBackground() throws Exception {
System.out.println("Calculating.");
Thread.sleep(3000);
return null;
}
};
sw.execute(); //Start
try {
sw.get(); //Wait
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
}
}
In each method of Calculations you create a new SwingWorker like you did and wait for it to finish by calling SwingWorker.get();
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 have created a GUI for starting a Thread which does something very simple. However, the child thread never starts.
The child thread, if started, will give some output; I don't get any output though. What am I missing?
Here's the Code:
The GUI class:
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
public class gui {
public static void main(String [] args) {
//final standalone s = new standalone();
final try2 t= new try2();
JFrame win = new JFrame();
win.setLayout(new FlowLayout());
JButton start = new JButton("Start");
JButton stop = new JButton("Stop");
start.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
t.t.start();
System.out.println("M on!");
try{
Thread.currentThread().sleep(10000);
}catch(Exception e1)
{
e1.printStackTrace();
}
System.out.println("M off!");
if(t.t.isInterrupted())
System.out.println("Stopped");
}
});
win.add(start);
win.add(stop);
win.setVisible(true);
}
}
And here is the Child Thread
public class try2 implements Runnable {
public Thread t;
int i;
try2() {
t=new Thread();
}
public void run() {
System.out.println(++i);
}
}
When you call t.t.start() it is starting the thread object in the t field of your try2 object. Unfortunately, this Thread has no Runnable, so when you start it, it will exit immediately. The try2.run() method is not called because the thread knows nothing about it.
Your code is convoluted. I'd simplify / fix it as follows:
Get rid of the try2.t field.
In the actionPerformed method create and run the thread as follows:
new Thread(t).start();
where t is your try2 instance.
And while you are fixing the code, try2 violates all Java style guides that I've ever come across. Class names should always start with a capital letter. Get into the habit of doing it right ...
Make your class try2 extends Thread (and remove the implements Runnable)., then simply call start() on your try2 instance.
Your class try2 should extend Thread (and implement the method run())
The way you are dealing with it, yuo are calling the run()-method of the thread-Object t inside try2. But the run()-method of this object is empty.
In my java swing application am having a Jframe and Jlabel for displaying current time.
here am using a thread for displaying time in jlablel which is added to the frame.my doubt is that when i dispose the jframe what will happen to the thread whether its running or stopped.
If you have NOT marked your thread as daemon by calling yourThread.setDaemon(true), it will keep running even if main thread in your application has finished. Remember you have to call setDaemon before starting the thread.
Refer my answer to some previous question for details.
The correct way in your case, I believe, would be you maintain a 'stop' flag which is watched by your timer thread. Timer thread should exit on reading this flag as 'false'. You can add a WindowListener to your jframe and on the window closed event set the 'stop' flag to true
Heres example code for what I am suggesting :
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
public class JFrameTest {
public static void main(String[] args) {
final Timer t = new Timer();
t.start();
JFrame jf = new JFrame("GOPI");
jf.setVisible(true);
jf.setSize(100, 100);
jf.addWindowListener(new WindowAdapter() {
#Override
public void windowClosing(WindowEvent e) {
t.stopTimer();
}
});
System.out.println("JFrameTest.main() DONE");
}
}
class Timer extends Thread {
boolean stop = false;
#Override
public void run() {
for (int i = 0; i < 50; i++) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
if (stop)
break;
System.out.println("Counting :" + i);
}
System.out.println("Timer exit");
}
public void stopTimer() {
stop = true;
}
}
Your thread will keep running.
You need to either do as suggested by Gopi or you could use System.exit(0) in close operation of your JFrame.
NOTE: I am assuming here that Your application needs to end if this Frame is closed.