如何在JavaFX应用程序内部等待JFrame线程完成？

Question

I'm trying to create a JFrame window from inside a JavaFX application. I'm using Oracle Java 8 and I'm able to do what I need in Linux, Windows but not in Mac OS. It seems like a JVM implementation issue. Here are my requirements:

• I need to call a library method which creates a game window(an extended class from JFrame). I need to be able to use keyboard in game.
• I can access the source code of the library but I don't have any intention to change the source code of the library
• I need to process game information after the game finished, so my main thread needs to wait until the game finishes

I created sample application below. Application works fine under Linux and Windows, but in Mac OS when I try to wait for the JFrame thread to finish app freezes and JFrame is not shown. SwingUtilities.invokeLater doesn't freeze but it doesn't wait for JFrame thread to finish. Since I need to wait for the JFrame thread invokeLater is not an option for me.

JFrameCreator.java

public class JFrameCreator implements Runnable {
    @Override
    public void run() {
        System.out.println("Creating JFrame");
        JFrame frame=new JFrame();
        frame.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
        frame.setSize(300,300);
        frame.setVisible(true);
        for (int i = 0; i < 100; i++) {
            frame.getContentPane().getGraphics().drawOval(150-i/2,150-i/2,i,i);
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

sample.fxml

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="100.0" prefWidth="200.0" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <Button layoutX="51.0" layoutY="10.0" mnemonicParsing="false" onAction="#createJFrame" text="New JFrame" />
      <RadioButton fx:id="cbThread" layoutX="10.0" layoutY="40.0" mnemonicParsing="false" selected="true" text="Thread">
         <toggleGroup>
            <ToggleGroup fx:id="tg" />
         </toggleGroup>
      </RadioButton>
      <RadioButton fx:id="cbInvokeWait" layoutX="10.0" layoutY="60.0" mnemonicParsing="false" text="invokeAndWait" toggleGroup="$tg" />
      <RadioButton fx:id="cbInvokeLater" layoutX="10.0" layoutY="80.0" mnemonicParsing="false" text="invokeLater" toggleGroup="$tg" />
   </children>
</AnchorPane>

Controller.java

public class Controller {
    @FXML RadioButton cbThread;
    @FXML RadioButton cbInvokeWait;
    @FXML RadioButton cbInvokeLater;

    public void createJFrame(javafx.event.ActionEvent actionEvent) {
        Runnable r=new JFrameCreator();
        try {
            if (cbThread.isSelected()) {
                Thread t=new Thread(new JFrameCreator());
                t.start();
                t.join();
            }
            else if(cbInvokeWait.isSelected())
                SwingUtilities.invokeAndWait(r);
            else
                SwingUtilities.invokeLater(r);
        }
         catch (InterruptedException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}

Main.java

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Swing in JavaFX");
        primaryStage.setScene(new Scene(root, 200, 100));
        primaryStage.show();
    }


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

I also tried a while loop with Thread.isAlive() method but that also behaves like Thread.join(). How can I achieve my requirements?

Answer 1

You could use one of the synchronization classes such as CountDownLatch . Pass it to your Runnable and call latch.countDown() at the end of the run() method. Meanwhile, your JavaFX thread would be paused on latch.await() . This will freeze the JavaFX UI, however, so this might not be what you want.

Another option would be to use a callback. Something like:

public class JFrameCreator implements Runnable {

    private final Runnable onFinished;

    public JFrameCreator(Runnable onFinished) {
        this.onFinished = onFinished;
    }

    @Override
    public void run() {
        // do your work...
        Platform.runLater(onFinished); // to communicate to JavaFX Application
                                       // Thread that JFrameCreator is complete
    }

}

This second option won't cause the JavaFX thread to wait but it does allow you to react at the appropriate time. You could change the type of onFinished to whatever you need; such as a Consumer if you want to pass the callback some object.