We Keep Coding

Force call paint after property changed [duplicate]

I have something I can't understand: my Swing GUI contains a 'play' and 'pause' button. I have also a static variable that defines 'ON' and 'OFF' states. (The main program generates the GUI).
By cliking on 'play' I change the state of my static variable to 'ON' and I launch a time-consuming process in a thread that also modifies the GUI. As long as the static variable is 'ON' loops in the same process. Clicking on 'pause' would change the static variable to OFF.
But by clicking on 'play' the GUI is freezing and consequently:
The GUI doesn't update
The process can't be 'paused' with my 'pause' button.
I have heard about EDT and SwingWorker but I you have a simple way to do it I take it.
Thank you for your help and forgive my bad english...

The problem is that you're doing the intensive, time-consuming work on the same thread responsible for updating the GUI. SwingWorker allows you to move time-consuming tasks to a separate thread of execution, thereby leaving the UI thread to do its thing uninhibited.
However, it does add a further complication: affinity. Calling methods on UI components generally requires that you do so from the UI thread. Therefore, you need to use special functionality to get back to the UI thread from the worker thread. SwingWorker also gives you this ability.
I suggest you read through this documentation.

You need to read Concurrency in Swing to understand how the EDT and SwingWorkers operate.
All GUI updates are executed on the EDT so when you click a GUI component any method that this calls will be executed on the EDT. If this is a time consuming process then this will block the EDT from executing any futher GUI updates. Hence your GUI is freezing and you can't click the pause button.
You need to use SwingWorker to execute the time consuming process on another thread. The link I provided above details how to do this.

You should not start long-running processes in Swing’s event handler because it will freeze your GUI, you know that now. :) Start it in a new thread. You only need to use a SwingWorker if you’re planning on manipulating the GUI from the worker thread (because Swing is not thread-safe).

This is a pretty straightforward reason: while Java is working on your time-consuming process, it isn't able to update the GUI. Solution: run the time-consuming process in a separate thread. There are a bunch of ways to program that, and it would probably depend somewhat on how your program is written.

The event dispatch thread (EDT) is the only thread in which it's safe to read or update the GUI.
The pause button should be setting the on/off variable in the event dispatch thread.
The time-consuming operation, and the loop, should not be in the EDT. (The loop should also not be running continuously doing nothing but check the variable, or it can easily eat all your CPU. If it has nothing else to do it should check, and then call Thread.sleep() for some length of time (say 100ms).)
If you can prove that the on/off variable is being set to OFF, but that nonetheless it's always read as ON, it may be that the variable's value is not being copied from the EDT to the worker thread. Make it volatile, or synchronize access to it, or use an AtomicReference, or read it in the EDT using SwingUtilities.invokeAndWait().
SwingWorker probably is the simplest way to go, here. Implement your time-consuming operation, and the on/off check, in the doInBackground() method, and your GUI update in the done() method.
public enum State {
RUNNING, STOPPED
}
public class ThreadSafeStateModel {
private State state = State.STOPPED;
public synchronized void stop() {
state = State.STOPPED;
}
public synchronized void start() {
state = State.RUNNING;
}
public boolean isRunning() {
return state == State.RUNNING;
}
}
public class ExpensiveProcessWorker extends SwingWorker<Void, Void> {
private final ThreadSafeStateModel model;
public ExpensiveProcessWorker(ThreadSafeStateModel model) {
this.model = model;
}
#Override // Runs in background
protected Void doInBackground() throws Exception {
while (model.isRunning()) {
// do one iteration of something expensive
}
return null;
}
#Override // Runs in event dispatch thread
protected void done() {
// Update the GUI
}
}
public class StopButton extends JButton {
public StopButton(final ThreadSafeStateModel model) {
super(new AbstractAction("Stop") {
#Override
public void actionPerformed(ActionEvent e) {
model.stop();
}
});
}
}
public class StartButton extends JButton {
public StartButton(final ThreadSafeStateModel model) {
super(new AbstractAction("Start") {
#Override
public void actionPerformed(ActionEvent e) {
model.start();
new ExpensiveProcessWorker(model).execute();
}
});
}
}
(A lot could be done to clean this up depending on the real application, but you get the idea.)

#Override
public void actionPerformed(ActionEvent e) {
new Thread() {
public void run() {
//your code which runs on click event
}
}.start();
}

can't get sequential behavior Java Swing [duplicate]

basically, I have this code which was initially working with console i/o now I have to connect it to UI. It may be completely wrong, I've tried multiple things although it still ends up with freezing the GUI.
I've tried to redirect console I/O to GUI scrollpane, but the GUI freezes anyway. Probably it has to do something with threads, but I have limited knowledge on it so I need the deeper explanation how to implement it in this current situation.
This is the button on GUI class containing the method that needs to change this GUI.
public class GUI {
...
btnNext.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
controller.startTest(index, idUser);
}
});
}
This is the method startTest from another class which contains instance of Question class.
public int startTest() {
for (int i = 0; i < this.numberofQuestions; i++) {
Question qt = this.q[i];
qt.askQuestion(); <--- This needs to change Label in GUI
if(!qt.userAnswer()) <--- This needs to get string from TextField
decreaseScore(1);
}
return actScore();
}
askQuestion method:
public void askQuestion() {
System.out.println(getQuestion());
/* I've tried to change staticaly declared frame in GUI from there */
}
userAnswer method:
public boolean userAnswer() {
#SuppressWarnings("resource")
Scanner scanner = new Scanner(System.in);
if( Objects.equals(getAnswer(),userInput) ) {
System.out.println("Correct");
return true;
}
System.out.println("False");
return false;
}
Thanks for help.

You're correct in thinking that it related to threads.
When you try executing code that will take a long time to process (eg. downloading a large file) in the swing thread, the swing thread will pause to complete execution and cause the GUI to freeze. This is solved by executing the long running code in a separate thread.
As Sergiy Medvynskyy pointed out in his comment, you need to implement the long running code in the SwingWorker class.
A good way to implement it would be this:
public class TestWorker extends SwingWorker<Integer, String> {
#Override
protected Integer doInBackground() throws Exception {
//This is where you execute the long running
//code
controller.startTest(index, idUser);
publish("Finish");
}
#Override
protected void process(List<String> chunks) {
//Called when the task has finished executing.
//This is where you can update your GUI when
//the task is complete or when you want to
//notify the user of a change.
}
}
Use TestWorker.execute() to start the worker.
This website provides a good example on how to use
the SwingWorker class.

As other answers pointed out, doing heavy work on the GUI thread will freeze the GUI. You can use a SwingWorker for that, but in many cases a simple Thread does the job:
Thread t = new Thread(){
#Override
public void run(){
// do stuff
}
};
t.start();
Or if you use Java 8+:
Thread t = new Thread(() -> {
// do stuff
});
t.start();

Pausing Swingworker

I hava a GUI that has a button that need to be pressed periodically in the sense it should pause in between. But i am not able to do that. I have tried with Thread.sleep(). Below is the code.
protected Object doInBackground() throws Exception {
while(true){
btnSend.doClick();
try {
Thread.sleep(2000);
continue;
} catch (InterruptedException e1) {
}
}
return null;
}
Can anyone tell me where i am going wrong and how to solve it?

You shouldn't use a SwingWorker for this since you should not call doClick() off the event thread. If al you want to do is make this call intermittently, then simply use a Swing Timer for calls that need to be done intermittently and on the event thread.
int timerDelay = 2000;
new Timer(timerDelay, new ActionListener() {
public void actionPerformed(ActionEvent evt) {
btnSend.doClick();
}
}).start();
Edit
You ask in comment:
But i need to update another UI on that button click event. If i dont use swingworker the other UI will freeze. I have to use swingworker. Is it possible to do so?
You've got it wrong, I fear. The button click and GUI code should all be on the EDT. Any background non-GUI code that is generated by the button click's ActionListener should be done in a SwingWorker but not the click itself.
e.g.,
elsewhere
btnSend.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
new SwingWorker<Void, Void>() {
public Void doInBackground() throws Exception {
//.....
return null;
}
}
}
});
If you need more specific advice regarding your situation, then you'll want to consider creating and posting a Minimal, Complete, and Verifiable Example Program where you condense your code into the smallest bit that still compiles and runs, has no outside dependencies (such as need to link to a database or images), has no extra code that's not relevant to your problem, but still demonstrates your problem.

Progress bars in Java

I have a code with two methods.
public void fondo() { ... } //Gathers JFrame Background and system time
public void recuperarDatosInternet() {...} //Connects to a URL and gets data.
When the JFrame is running, at the beginning it takes four or five seconds to perform all the operations of those methods.
While it's loading, the frame displays totally empty for 3 or 4 seconds until all the methods are complete, then the frame shows up and it's all right.
How can I make a Progress Bar that shows the user that something it's loading?
I don't mean a ProgressBar that are predetermined to take "4000 ms". I am referring to a progressbar that can take whatever it takes, and the bar doesn't reach the 100% until the methods are complete.

You could use a SwingWorker for this. This class enables allows the time-consuming work to be done in background thread and does not hold up the user-interface in the meantime. It also has the facility to divide the work up into 'chunks' and to update the user-interface on the completion of these chunks of work. This is what you would need for a progress bar, although it depends on your task being 'chunkable'. The link above takes you to the JavaDoc for this class which contains an example for both the simple and the 'chunked' usage.

If you run heavy task in The Event Dispatch Thread it's gonna to freeze until finish to avoid that you can execute the download in another thread using SwingWorker.
Follow this link to see a complete example with progressBar , special attention to setProgress() publish() and process().
Example:
public class MyWorker extends SwingWorker<Integer, String> {
#Override
protected Integer doInBackground() throws Exception {
// Start
publish("Start Download");
setProgress(1);
// More work was done
publish("More work was done");
setProgress(10);
// Complete
publish("Complete");
setProgress(100);
return 1;
}
#Override
protected void process(List< String> chunks) {
// Messages received from the doInBackground() (when invoking the publish() method)
}
}
and in client code:
SwingWorker worker = new MyWorker();
worker.addPropertyChangeListener(new MyProgressListener());
worker.execute();
class MyProgressListener implements PropertyChangeListener {
#Override
public void propertyChange(final PropertyChangeEvent event) {
if(event.getPropertyName().equalsIgnoreCase("progress")) {
downloadProgressBar.setIndeterminate(false);
downloadProgressBar.setValue((Integer) event.getNewValue());
}
}
}

How can I push a selected tab update (java swing)?

I'm trying to update the tab being displayed, however it seems to wait until the end of the method and then update. Is there a way to make the tab being displayed update immediately?
Here is an example of the code where I'm having this issue:
private static void someButtonMethod()
{
Button = new JButton("My Button");
Button(new ActionListener() {
public void actionPerformed(ActionEvent e)
{
tabs.setSelectedIndex(1);
// Do some other things (In my case run a program that takes several seconds to run).
runProgram();
}
});
}

The reason for this is that the method is being executed in the Event Dispatch thread, and any repaint operations will also occur in this thread. One "solution" is to update the tab index and then schedule the remaining work to be invoked later on the EDT; this should cause the tab state to be updated immediately; e.g.
public void actionPerformed(ActionEvent evt) {
tab.setSelectedIndex(1);
SwingUtilities.invokeLater(new Runnable() {
public void run() {
// Do remaining work.
}
});
}
EDIT
Per your comment below an example of how to invoke a SwingWorker in order to call your runProgram method would look something like this:
// Typed using Void because runProgram() has no return value.
new SwingWorker<Void, Void>() {
protectedVoid doInBackground() {
runProgram();
return null; // runProgram() doesn't return anything so return null.
}
protected void done() {
// Called on the EDT when the background computation has completed.
// Could insert code to update UI here.
}
}.execute()
However, I sense a bigger problem here: The fact that you are seeing a significant delay in updating the tab makes me think you are performing long running calculations on the EDT. If this is the case you should consider performing this work on a background thread. Take a look at the SwingWorker class.