Threading

Updating the UI using Platform.runLater

Long-running operations must not be run on the JavaFX application thread, since this prevents JavaFX from updating the UI, resulting in a frozen UI.

Furthermore any change to a Node that is part of a “live” scene graph must happen on the JavaFX application thread. Platform.runLater can be used to execute those updates on the JavaFX application thread.

The following example demonstrates how to update a Text Node repeatedly from a different thread:

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class CounterApp extends Application {

    private int count = 0;
    private final Text text = new Text(Integer.toString(count));

    private void incrementCount() {
        count++;
        text.setText(Integer.toString(count));
    }

    @Override
    public void start(Stage primaryStage) {
        StackPane root = new StackPane();
        root.getChildren().add(text);

        Scene scene = new Scene(root, 200, 200);

        // longrunning operation runs on different thread
        Thread thread = new Thread(new Runnable() {

            @Override
            public void run() {
                Runnable updater = new Runnable() {

                    @Override
                    public void run() {
                        incrementCount();
                    }
                };

                while (true) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException ex) {
                    }

                    // UI update is run on the Application thread
                    Platform.runLater(updater);
                }
            }

        });
        // don't let thread prevent JVM shutdown
        thread.setDaemon(true);
        thread.start();

        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }

}

Grouping UI updates

The following code makes the UI unresponsive for a short while after the button click, since too many Platform.runLater calls are used. (Try scrolling the ListView immediately after the button click.)

@Override
public void start(Stage primaryStage) {
    ObservableList<Integer> data = FXCollections.observableArrayList();
    ListView<Integer> listView = new ListView<>(data);
    
    Button btn = new Button("Say 'Hello World'");
    btn.setOnAction((ActionEvent event) -> {
        new Thread(() -> {
            for (int i = 0; i < 100000; i++) {
                final int index = i;
                Platform.runLater(() -> data.add(index));
            }
        }).start();
    });

    Scene scene = new Scene(new VBox(listView, btn));

    primaryStage.setScene(scene);
    primaryStage.show();
}

To prevent this instead of using a large number of updates, the following code uses a AnimationTimer to run the update only once per frame:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.animation.AnimationTimer;

public class Updater {

    @FunctionalInterface
    public static interface UpdateTask {

        public void update() throws Exception;
    }

    private final List<UpdateTask> updates = new ArrayList<>();

    private final AnimationTimer timer = new AnimationTimer() {

        @Override
        public void handle(long now) {
            synchronized (updates) {
                for (UpdateTask r : updates) {
                    try {
                        r.update();
                    } catch (Exception ex) {
                        Logger.getLogger(Updater.class.getName()).log(Level.SEVERE, null, ex);
                    }
                }
                updates.clear();
                stop();
            }
        }
    };

    public void addTask(UpdateTask... tasks) {
        synchronized (updates) {
            updates.addAll(Arrays.asList(tasks));
            timer.start();
        }
    }

}

which allows grouping the updates using the Updater class:

private final Updater updater = new Updater();

...

        // Platform.runLater(() -> data.add(index));
        updater.addTask(() -> data.add(index));

How to use JavaFX Service

Instead of running intensive tasks into JavaFX Thread that should be done into a Service.So what basically is a Service?

A Service is a class which is creating a new Thread every time you are starting it and is passing a Task to it to do some work.The Service can return or not a value.

Below is a typical example of JavaFX Service which is doing some work and return a Map<String,String>():

public class WorkerService extends Service<Map<String, String>> {

    /**
     * Constructor
     */
    public WorkerService () {

        // if succeeded
        setOnSucceeded(s -> {
            //code if Service succeeds
        });

        // if failed
        setOnFailed(fail -> {
            //code it Service fails
        });

        //if cancelled
        setOnCancelled(cancelled->{
            //code if Service get's cancelled
        });
    }

    /**
    * This method starts the Service
    */
    public void startTheService(){
        if(!isRunning()){
           //...
           reset();
           start();
        }

    }

    @Override
    protected Task<Map<String, String>> createTask() {
        return new Task<Map<String, String>>() {
            @Override
            protected Void call() throws Exception {

                    //create a Map<String, String>
                    Map<String,String> map  = new HashMap<>();

                   //create other variables here

                   try{
                        //some code here
                        //.....do your manipulation here

                        updateProgress(++currentProgress, totalProgress);
                    }

                } catch (Exception ex) {                  
                    return null; //something bad happened so you have to do something instead of returning null
                }

                return map;
            }
        };
    }

}