I am learning about multithreading right now.
I have a "main" class in which I build a JFrame with a Textfield and a Start and a Stop Button in it.
I also have another class/Thread from which I want to print the current time into my Textfield when I click the Start Button of my Frame. Everything works but the text doesn't change in my Textfield as I start the Thread even though Eclipse says my code is alright.
What am I doing wrong?
Class 1:
public class Uhr extends JFrame {
private JPanel contentPane;
public JTextPane tpZeit;
Thread t;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Uhr frame = new Uhr();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public Uhr() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
tpZeit = new JTextPane();
tpZeit.setText("test");
tpZeit.setBounds(43, 50, 212, 43);
contentPane.add(tpZeit);
JButton btnstart = new JButton("GO");
btnstart.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
tpZeit.setText("started");
if (t == null) {
t = new Thread(new Uhrsteuerung());
}
if(!t.isAlive()) {
t = new Thread(new Uhrsteuerung());
t.start();
}
}
});
btnstart.setBounds(10, 227, 89, 23);
contentPane.add(btnstart);
JButton btnstop = new JButton("Stop");
btnstop.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
t.interrupt();
}
});
btnstop.setBounds(248, 227, 89, 23);
contentPane.add(btnstop);
}
}
Class with additional Thread:
public class Uhrsteuerung extends Uhr implements Runnable {
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
String time;
boolean x ;
#Override
public synchronized void run() {
// TODO Auto-generated method stub
x = true;
while (x) {
try {
time = sdf.format(System.currentTimeMillis());
System.out.println(time);
tpZeit.setText(time);
repaint();
Thread.sleep(1000);
} catch (InterruptedException ex) {
x = false;
}
}
}
}
All code for Java's Swing classes must be executed on the Event Dispatch Thread (EDT). Swing provides some special classes for helping you do this.
To execute code off the EDT, use a SwingWorker class. SwingWorker will execute a task in the background (not using the EDT) and then return a result properly synchronized that executes on the EDT. https://docs.oracle.com/en/java/javase/16/docs/api/java.desktop/javax/swing/SwingWorker.html
Its application is pretty simple. Define your own class that extends SwingWorker.
class PrimeNumbersTask extends SwingWorker<List<Integer>, Integer> {
// ...
If you need to update a component, it's good to pass in the component so that you can refer to it later.
class PrimeNumbersTask extends SwingWorker<List<Integer>, Integer> {
private JTextArea textArea;
public PrimeNumbersTask( JTextArea textArea ) {
this.textArea = textArea;
}
// ...
Do your work in the method doInBackground() by overriding it. Don't touch the Swing classes in this method. Use the publish() method to send smaller chunks of data to the EDT if you want to provide progressive results instead of waiting for the whole task to complete.
#Override
public List<Integer> doInBackground() {
while (!done && ! isCancelled()) {
// do stuff
publish(number);
setProgress(100 * numbers.size() / numbersToFind);
}
}
return numbers;
}
Finally override the method process() to update your Swing classes.
#Override
protected void process(List<Integer> chunks) {
for (int number : chunks) {
textArea.append(number + "\n");
}
}
From the EDT, you can call execute() to start your background task.
JTextArea textArea = new JTextArea();
// manipulate and set up GUI...
PrimeNumbersTask task = new PrimeNumbersTask(textArea);
task.execute();
There's a lot more docs on SwingWorker if you Google for it, that's the basics of how to use it.
Related
I've downloaded a small Java project from oracle website to create a progress bar.
I understand it, but I need to apply it in a different way, the application is creating a thread in the background so the progress bar can be updated accordingly (doInBackground()).
My question is, how can I replace this kind of process in the background in this application by a method from my application (method is just doing a kind of batch processing on a database), can someone help please?
Here is code by Oracle:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.beans.*;
import java.util.Random;
public class ProgressBarDemo2 extends JPanel
implements ActionListener, PropertyChangeListener {
private JProgressBar progressBar;
private JButton startButton;
private JTextArea taskOutput;
private Task task;
class Task extends SwingWorker<Void, Void> {
/*
* Main task. Executed in background thread.
*/
#Override
public Void doInBackground() {
Random random = new Random();
int progress = 0;
//Initialize progress property.
setProgress(0);
//Sleep for at least one second to simulate "startup".
try {
Thread.sleep(1000 + random.nextInt(2000));
} catch (InterruptedException ignore) {}
while (progress < 100) {
//Sleep for up to one second.
try {
Thread.sleep(random.nextInt(1000));
} catch (InterruptedException ignore) {}
//Make random progress.
progress += random.nextInt(10);
setProgress(Math.min(progress, 100));
}
return null;
}
/*
* Executed in event dispatch thread
*/
public void done() {
Toolkit.getDefaultToolkit().beep();
startButton.setEnabled(true);
taskOutput.append("Done!\n");
}
}
public ProgressBarDemo2() {
super(new BorderLayout());
//Create the demo's UI.
startButton = new JButton("Start");
startButton.setActionCommand("start");
startButton.addActionListener(this);
progressBar = new JProgressBar(0, 100);
progressBar.setValue(0);
//Call setStringPainted now so that the progress bar height
//stays the same whether or not the string is shown.
progressBar.setStringPainted(true);
taskOutput = new JTextArea(5, 20);
taskOutput.setMargin(new Insets(5,5,5,5));
taskOutput.setEditable(false);
JPanel panel = new JPanel();
panel.add(startButton);
panel.add(progressBar);
add(panel, BorderLayout.PAGE_START);
add(new JScrollPane(taskOutput), BorderLayout.CENTER);
setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
}
/**
* Invoked when the user presses the start button.
*/
public void actionPerformed(ActionEvent evt) {
progressBar.setIndeterminate(true);
startButton.setEnabled(false);
//Instances of javax.swing.SwingWorker are not reusuable, so
//we create new instances as needed.
task = new Task();
task.addPropertyChangeListener(this);
task.execute();
}
/**
* Invoked when task's progress property changes.
*/
public void propertyChange(PropertyChangeEvent evt) {
if ("progress" == evt.getPropertyName()) {
int progress = (Integer) evt.getNewValue();
progressBar.setIndeterminate(false);
progressBar.setValue(progress);
taskOutput.append(String.format(
"Completed %d%% of task.\n", progress));
}
}
/**
* Create the GUI and show it. As with all GUI code, this must run
* on the event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("ProgressBarDemo2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new ProgressBarDemo2();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
First, I'd recommend by defining a concept of a "progressable" state
public interface Progressable {
public void setProgress(int progress); // I prefer double, but we'll keep it inline with the rest of the API
}
Then, the entry point for your tasks would take a reference to Progressable
public class MySuperAwesomeLongRunningTask ... {
//...
private Progressable progressable;
public void performTask(Progressable progressable) {
this.prgressable = progressable
}
protected void methodThatDoesSomeWork() {
// Do some super duper work...
// calculate the progress of that work some how,
// based on your implementation...
int progress = ...;
progressable.setProgress(progress);
}
}
Then, create a SwingWorker which implements Progressable and calls your work...
class Task extends SwingWorker<Void, Void> implements Progressable {
private MySuperAwesomeLongRunningTask taskToBeDone;
public Task(MySuperAwesomeLongRunningTask taskToBeDone) {
self.taskToBeDone = taskToBeDone;
}
/*
* Main task. Executed in background thread.
*/
#Override
public Void doInBackground() {
taskToBeDone.performTask(this);
return null;
}
/*
* Executed in event dispatch thread
*/
public void done() {
// What ever you need to do...
}
}
Now, because SwingWorker already has a method called setProgress(int) it automatically conforms to Progressable (so long as you implement it), so when MySuperAwesomeLongRunningTask calls setProgress, it will actually be calling the SwingWorkers implementation.
This means, that the rest of the code basically remains the same, expect, I'd change
if ("progress" == evt.getPropertyName()) {
to
if ("progress".equals(evt.getPropertyName())) {
because comparing Strings with == is bad idea (and freaks me out :P)
I have a JButton that will not allow me to perform the same action on any subsequent click on it after the first in the same Swing GUI instance.
JButton Run = new JButton("Run");
Run.setLocation(290, 70);
Run.setSize(120, 30);
buttonPanel.add(Run);
Run.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (Run.isEnabled()) {
errorLabel.setText("");
Result result = JUnitCore.runClasses(Run.class);
errorMessageDisplay(result);
}
}
});
totalGUI.setOpaque(true);
return totalGUI;
}
So far I thought about and tried removing the JPanel and painting all of the buttons back on, and disabling/renabling buttons.
The errorMessageDisplay method is as follows:
public void errorMessageDisplay(Result resultPass) {
if (resultPass.getFailureCount() > 0) {
errorLabel.setForeground(Color.red);
errorLabel.setVisible(true);
errorLabel.setText(" Failed");
}
else {
errorLabel.setForeground(Color.green);
errorLabel.setText(" Passed");
errorLabel.setVisible(true);
}
}
At first glance, the JUnitCore.runClasses(Run.class); call is suspicous. Also, it would be good to know what does the errorMessageDisplay() do. I believe, the problem is with one of these methods.
You can verify this with the following experimental code. Just be careful not to push it into production.
JButton run = new JButton("Run");
run.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (Run.isEnabled()) {
errorLabel.setText("");
System.out.println("Run action peformed.");
}
}
Update Since the errorMessageDisplay() looks okay, it's probably a Threading problem with JUniCore. Thus I'd try the following code:
final ExecutorService executor = Executors.newFixedThreadPool(5); // this runs stuff in background
JButton run = new JButton("Run");
// ..
run.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (Run.isEnabled()) {
executor.execute(new Runnable() { // This is how we run stuff in background. You can use lambdas instead of Runnables.
public void run() {
final Result result = JUnitCore.runClasses(Run.class); // Run.class is different from the current JButton run.
SwingUtilities.invokeLater(new Runnable() { // Now we go back to the GUI thread
public void run() {
errorMessageDisplay(result);
}
});
}
});
}
});
Consider this basic Swing program, consisting out of two buttons:
public class main {
public static void main(String[] args) {
JFrame jf = new JFrame("hi!");
JPanel mainPanel = new JPanel(new GridLayout());
JButton longAction = new JButton("long action");
longAction.addActionListener(event -> doLongAction());
JButton testSystemOut = new JButton("test System.out");
testSystemOut.addActionListener(event -> System.out.println("this is a test"));
mainPanel.add(longAction);
mainPanel.add(testSystemOut);
jf.add(mainPanel);
jf.pack();
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.setVisible(true);
}
public static void doLongAction() {
SwingUtilities.invokeLater(() -> {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
System.out.println("Interrupted!");
}
System.out.println("Finished long action");
});
}
}
I want my second button testSystemOut to be usable while the first one is working on its long action (here, I put a 3 second sleep in it). I can do that by manually putting doLongAction() in a Thread and call start(). But I've read I should use SwingUtilities instead, which works exactly like EventQueue here. However, if I do so, my Button freezes for the duration of its action.
Why?
By using SwingUtilities.invokeLater, you are calling the enclosed code, including the Thread.sleep(...) call, on the Swing event thread, which is something you should never do since it puts the entire event thread, the thread responsible for drawing your GUI's and responding to user input, to sleep -- i.e., it freezes your application. Solution: use a Swing Timer instead or do your sleeping in a background thread. If you are calling long-running code and using a Thread.sleep(...) to simulate it, then use a SwingWorker to do your background work for you. Please read Concurrency in Swing for the details on this. Note that there is no reason for the SwingUtilities.invokeLater where you have it since the ActionListener code will be called on the EDT (the Swing event thread) regardless. I would however use SwingUtilities.invokeLater where you create your GUI.
e.g.,
import java.awt.*;
import java.awt.event.*;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.concurrent.ExecutionException;
import javax.swing.*;
public class Main {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame jf = new JFrame("hi!");
JPanel mainPanel = new JPanel(new GridLayout());
JButton testSystemOut = new JButton("test System.out");
testSystemOut.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println("this is a test");
}
});
mainPanel.add(new JButton(new LongAction("Long Action")));
mainPanel.add(new JButton(new TimerAction("Timer Action")));
mainPanel.add(testSystemOut);
jf.add(mainPanel);
jf.pack();
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.setVisible(true);
}
});
}
#SuppressWarnings("serial")
public static class LongAction extends AbstractAction {
private LongWorker longWorker = null;
public LongAction(String name) {
super(name);
int mnemonic = (int) name.charAt(0);
putValue(MNEMONIC_KEY, mnemonic);
}
#Override
public void actionPerformed(ActionEvent e) {
setEnabled(false);
longWorker = new LongWorker(); // create a new SwingWorker
// add listener to respond to completion of the worker's work
longWorker.addPropertyChangeListener(new LongWorkerListener(this));
// run the worker
longWorker.execute();
}
}
public static class LongWorker extends SwingWorker<Void, Void> {
private static final long SLEEP_TIME = 3 * 1000;
#Override
protected Void doInBackground() throws Exception {
Thread.sleep(SLEEP_TIME);
System.out.println("Finished with long action!");
return null;
}
}
public static class LongWorkerListener implements PropertyChangeListener {
private LongAction longAction;
public LongWorkerListener(LongAction longAction) {
this.longAction = longAction;
}
#Override
public void propertyChange(PropertyChangeEvent evt) {
if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
// if the worker is done, re-enable the Action and thus the JButton
longAction.setEnabled(true);
LongWorker worker = (LongWorker) evt.getSource();
try {
// call get to trap any exceptions that might have happened during worker's run
worker.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
}
}
#SuppressWarnings("serial")
public static class TimerAction extends AbstractAction {
private static final int TIMER_DELAY = 3 * 1000;
public TimerAction(String name) {
super(name);
int mnemonic = (int) name.charAt(0);
putValue(MNEMONIC_KEY, mnemonic);
}
#Override
public void actionPerformed(ActionEvent e) {
setEnabled(false);
new Timer(TIMER_DELAY, new TimerListener(this)).start();
}
}
public static class TimerListener implements ActionListener {
private TimerAction timerAction;
public TimerListener(TimerAction timerAction) {
this.timerAction = timerAction;
}
#Override
public void actionPerformed(ActionEvent e) {
timerAction.setEnabled(true);
System.out.println("Finished Timer Action!");
((Timer) e.getSource()).stop();
}
}
}
Don't use SwingUtilities.invokeLater(...) when you want to execute some long-running code. Do that in a separate normal thread.
Swing is not multi-threaded, it's event-driven. Because of that there are methods like SwingUtilities.invokeLater(...). You have to use those methods if you want to alter Swing-Components from a different thread (since Swing is not thread-safe), for example if you want to change a Button's text.
Everything thats GUI-Related runs in that Swing-Thread, e.g. Cursor-Blinks, Messages from the OS, User Commands, etc.
Since its a single thread, every long running Code in this thread it will block your GUI.
If you just do some long-running code that isn't GUI-related, it shouldn't run in the Swing-Event-Thread, but in its own separated thread.
See
https://weblogs.java.net/blog/kgh/archive/2004/10/multithreaded_t.html
for why Swing is not Multi-Threaded.
I have a simple question relating to iPOJO.
When a component iPOJO sleeps, all remaining components will also disable although there are not dependencies between them. Why? Here's an example:
Component 1:
#Component(name="frame1", immediate=true)
#Instantiate(name="iframe1")
public class Frame1 implements Runnable{
String str;
Label lb = new Label();
TextField tf = new TextField();
Frame fr;
public void run() {
fr = new Frame("Frame1");
fr.setLayout(new BorderLayout());
fr.setSize(230, 200);
fr.setLocation(900,250);
fr.add(tf, BorderLayout.NORTH);
lb.setText("Result");
fr.add(lb, BorderLayout.CENTER);
Panel pn = new Panel();
fr.add(pn, BorderLayout.SOUTH);
pn.setLayout(new GridLayout(1,4,1,1));
Button bt = new Button("Printer 1");
pn.add(bt);
bt.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
try {
System.out.println("start sleep");
Thread.sleep(5000);
System.out.println("stop sleep");
} catch (InterruptedException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
});
fr.setVisible(true);
}
#Validate
public void start() {
//this.delayService = dls;
Thread th = new Thread(this);
th.start();
}
#Invalidate
public void stop() {
System.out.println("stop");
fr.setVisible(false);
}
}
Component 2:
#Component(name="frame2", immediate=true)
#Instantiate(name="iframe2")
public class Frame2 implements Runnable{
String str;
Label lb = new Label();
TextField tf = new TextField();
Frame fr;
public void run() {
System.out.println("start component 2");
fr = new Frame("Frame2");
fr.setLayout(new BorderLayout());
fr.setSize(230, 200);
fr.setLocation(900,250);
fr.add(tf, BorderLayout.NORTH);
lb.setText("Result");
fr.add(lb, BorderLayout.CENTER);
Panel pn = new Panel();
fr.add(pn, BorderLayout.SOUTH);
pn.setLayout(new GridLayout(1,4,1,1));
Button bt = new Button("Printer 2");
pn.add(bt);
bt.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
System.out.println("in 2");
}
});
fr.setVisible(true);
}
#Validate
public void start() throws Exception {
//this.delayService = dls;
System.out.println("start thread 2");
Thread th = new Thread(this);
th.start();
//fr.setVisible(true);
}
#Invalidate
public void stop() throws Exception {
System.out.println("stop");
fr.setVisible(false);
}
}
Two components are deployed and running. There are two independent components. But I click the "Printer 1" button. "frame1" component is sleeping during 5s. And during these 5 seconds, i can't click "Printer 2" of "frame2" component.
This is not an ipojo issue. Swing uses one thread (and only one thread) in order to dispatch events such as clicks. When you click your first button, swing runs your actionPerformed in this thread. This method puts your thread to sleep for 5 seconds. This means that the thread responsible for event handling cannot do anything during this time. This is why your program does not respond to your second click.
Whenever you have a long computation in swing (and also osgi), it is often a good idea to run your code in a separate thread in order to avoid blocking the execution (here you have a useless Thread.sleep() but I guess you could have an http request or anything that may take a long time instead). You should probably use an executor service or anything similar.
I have a constructor of a JFrame where I have a Thread(t1) which is running thanks to a
while(true)
I would like to know how to implement my JFrame so it can kill the thread when I close it, because t1 need to be running when the JFrame is active
EDIT:
Here is the code:
public class Vue_Session extends JFrame {
private JPanel contentPane;
private int idsess;
private User u;
public Vue_Session(User us, int id) {
this.u = us;
this.idsess = id;
toServ t=new toServ(idsess);
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
setBounds((int) screenSize.getWidth() / 2 - 800 + (800 / 2), 90, 800,
600);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(new BorderLayout());
Vue_Idee vueIdee = new Vue_Idee(this.idsess, this.u);
contentPane.add(vueIdee, BorderLayout.SOUTH);
Vue_IdeeSession vueSess = new Vue_IdeeSession(this.idsess);
contentPane.add(vueSess, BorderLayout.CENTER);
Thread t1 = new Thread( new Runnable(){
public void run(){
while(true){
try{
Thread.sleep(500);
}catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
t.getIdee();
vueSess.act();
revalidate();
}
}
});
t1.start();
}
You can handle it with a boolean variable like
boolean end = false;
while (!end){...}
Also I suggest you use ExecutorService or ForkJoinPool so you can simply control your tasks, threads, etc
EDIT:
boolean end = false;
new Thread(() -> {
while (!end) {
//...
}
}).start();
and this is where you should end your tasks:
addWindowListener(new java.awt.event.WindowAdapter() {
public void windowClosed(java.awt.event.WindowEvent evt) {
end = true;
System.exit(0);
// or this.dispose();
}
});
good luck :)
It's a controversial topic but in general I would replace the while (true) construct with
while(!Thread.currentThread().isInterrupted()){
try{
Thread.sleep(500);
}catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
t.getIdee();
vueSess.act();
revalidate();
}
More information on this topic can be found here:
http://www.javaspecialists.eu/archive/Issue056.html
Okay, here was the answer:
I needed to add en WindowListenne:
addWindowListener(new WindowAdapter() {
#Override
public void windowClosing(WindowEvent b) {
t1.stop();
dispose();
}
});
And also:
setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
First, you need to make the thread kill-able. To do this, instead of looping forever, loop as long as certain looping flag is true.
After that, you need to create a listener that gets called whenever the user closes the frame. You can use WindowAdapter to do this. When the listener is called, set the looping flag to false. Once the thread dies, you can safely terminate the program.
For example:
public class Vue_Session extends JFrame {
Thread thread = null;
boolean threadAlvie = true;
boolean threadDie = false;
public Vue_Session(User us, int id) {
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent windowEvent) {
threadAlive = false;
// Wait until the thread dies
while (!threadDie) {
// Sleep for 100 milliseconds.
Thread.sleep(100);
}
System.exit(0);
}
});
thread = new Thread(new Runnable() {
public void run(){
while (threadAlive){
// do something
}
threadDie = true;
}
});
thread.start();
}
}