Java

What is the difference between a static and an instance variable in Java?

5-Sep-23 22:43

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Ashley OP7-Aug-23 23:31

Ashley OP

7-Aug-23 23:31

What is the difference between a static and an instance variable in Java?

Re: What is the difference between a static and an instance variable in Java?

Richard MacCutchan7-Aug-23 23:33

JavaFX multithreading operation changing GUI elements

7-Aug-23 23:33

See Java Tutorials Learning Paths[^].

JohnCodding21-Jul-23 6:37

JohnCodding

21-Jul-23 6:37

I want to make it so that when the user launches the app, it will display the GUI but at the same time it will launch other threads (multithreading) that will do some calculations and when those are finished they will update some GUI elements (which are always created before the thread with calculations is launched, that is not a problem of getting null), also when a button is pressed same as before using multithreading it will do some calculation and update the GUI after each thread is done.

Now the problem I have is that if you are using Thread(new Runnable)/start(); to launch multiple threads (even one) you get into the error Not on FX application thread. As possible solutions I read about JavaFX Task and Service but those were freezing the GUI thread until they were done.

This is what I tried ("Functions.functionX" is the placeholder, the real function takes between 0-20 seconds to finish):

button.setOnAction(event -> {
    Service<Void> doSomething = new Service<Void>() {
        @Override
        protected Task<Void> createTask() {
            Functions.functionX("parameter");
            return null;
        }
    };
    doSomething.start();
});

Now the problem with this is like I said, when the button is pressed, the GUI is unusable until the function finishes. Using straight Task had the same effect unfortunately.
What do I need to change/add to make it so that I can launch multiple threads at a time, and inside them to change elements from GUI (right now I only want to update some Labels with .setText() inside those threads, each thread updates one Label)?

modified 21-Jul-23 13:02pm.

Re: JavaFX multithreading operation changing GUI elements

JudyL_MD21-Jul-23 9:01

JudyL_MD

21-Jul-23 9:01

Where do you get the "Not on FX application thread" error? When trying to launch all those threads or when you try to update the GUI from within one of those threads? If it's the former, I can't help. If it's the latter, you simply need to run your update code on the UI thread. I don't use JavaFX but in my Java / Android, this works fine.

Java

// called from a fragment
Thread worker = new Thread (new Runnable ()
{
    @Override public void run ()
    {
        // stuff to do not on the UI thread
        // ...

        // stuff is done, time to tell the UI
        activity.runOnUiThread (new Runnable ()
        {
            @Override public void run ()
            {
                // code that touches the UI
            }
        });
    }
});
worker.start ();

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modified 21-Jul-23 15:11pm.

Re: JavaFX multithreading operation changing GUI elements

JohnCodding21-Jul-23 9:44

JohnCodding

21-Jul-23 9:44

I get the error when I call .setText(). Everything related to the GUI must run on FX thread, but if you are running something intensive on that, then the interface will freeze, that is why you should run that on a different thread and make the updates later.

Re: JavaFX multithreading operation changing GUI elements

JudyL_MD21-Jul-23 10:46

JudyL_MD

21-Jul-23 10:46

And that is exactly what my code does. It creates the thread worker from the UI thread and starts it. It then exits that UI function, effectively releasing the UI thread. Meanwhile, worker is executing its Run method separately from the UI. After it finishes doing stuff, worker then creates and runs a UI thread that updates the UI. JavaFX may have a different method to call instead of runOnUiThread, but the logic is the same. JavaFX has to have an equivalent.

Don't be confused by the code appearing to all be in the initial UI function. Each of those Run methods is a chunk of code that executes in a separate and distinct thread.

One caveat -- when running on Android, I have found that this doesn't always work to release the UI when it is done from within view creation / fragment startup. I don't know if JavaFX has the same issue. What I've shown works when launched from the UI once the screen is up and established; for example, from a menu item click handler.

Be wary of strong drink. It can make you shoot at tax collectors - and miss.
Lazarus Long, "Time Enough For Love" by Robert A. Heinlein

Re: JavaFX multithreading operation changing GUI elements

JohnCodding21-Jul-23 9:49

JohnCodding

21-Jul-23 9:49

I managed to make it work but not with Task or Service. On button action I created a new Thread thread = new Thread(new Runnable() {...});, and after I was done with the calculation, still inside thread run function I called:

Platform.runLater(new Runnable() {
    @Override
    public void run() {
        label.setText(newValue);
    }
});

I am still interested what I should do to make it work with those too, if someone can explain what I was doing wrong.

Operator precedence

darek2902198812-Jul-23 5:41

12-Jul-23 5:41

I am complete fresher at Java. Could You help me with https://www.udemy.com/course/learn-java-to-master/learn/quiz/5933562#questions task, please?

Dave Kreskowiak12-Jul-23 6:11

Dave Kreskowiak

12-Jul-23 6:11

Asking the same question will not change the answers.

No, we're not doing your work for you, and you haven't described a problem you're having.

Asking questions is a skill
CodeProject Forum Guidelines
Google: C# How to debug code
Seriously, go read these articles.

Dave Kreskowiak

Operator precedence

darek2902198811-Jul-23 3:06

11-Jul-23 3:06

I am complete fresher at Java. Could You help me with https://www.udemy.com/course/learn-java-to-master/learn/quiz/5933562#questions task, please?

Richard Deeming11-Jul-23 3:30

Richard Deeming

11-Jul-23 3:30

No, nobody here is going to help you cheat on a test.

If you can't answer the questions after taking the course, then go back and review the course again. If you still can't answer the questions, then find a better course.

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

darek2902198812-Jul-23 5:44

12-Jul-23 5:44

My solution:

public class Exercise {
double a = 234.89;
double b = 789.456;
double c = 567.89;
double d = 78.345;
 
double e = System.out.println(((a+b) * (c-d)) / (a/d));
double f = System.out.println(((a*b) + (c/d)) - (a-d));
if(e>f):
println(e);
else:
println(f);
}

jeron112-Jul-23 6:15

jeron1

12-Jul-23 6:15

Your solution to what? Can you describe your problem? and no, I'm not going to follow a link.

"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
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Richard MacCutchan11-Jul-23 5:24

11-Jul-23 5:24

You can find the answer(s) at Java Tutorials Learning Paths[^].

darek2902198812-Jul-23 5:46

12-Jul-23 5:46

public class Exercise {
double a = 234.89;
double b = 789.456;
double c = 567.89;
double d = 78.345;
 
double e = System.out.println(((a+b) * (c-d)) / (a/d));
double f = System.out.println(((a*b) + (c/d)) - (a-d));
if(e>f):
println(e);
else:
println(f);
}

Richard MacCutchan12-Jul-23 6:15

12-Jul-23 6:15

And what happens when you run this code?

Andre Oosthuizen14-Jul-23 1:36

Andre Oosthuizen

14-Jul-23 1:36

It's going to crash as he cannot assign the result of his method to a variable like his trying to do with 'double e' and 'double f'.

For him to assign the result to variables, he need to separate his calculation and printing steps. Confused | :confused:

Richard MacCutchan14-Jul-23 1:52