Launch JavaFX application from another class

Suppose this is our JavaFX class:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.Stage;

public class OKButton extends Application {

    @Override
    public void start(Stage stage) {
        Button btn = new Button("OK");
        Scene scene = new Scene(btn, 200, 250);
        stage.setTitle("OK");
        stage.setScene(scene);
        stage.show();
    }
}

Then we may launch it from another class like this:

import javafx.application.Application;

public class Main {
    public static void main(String[] args) {
        Application.launch(OKButton.class, args);
    }
}

I had the same problem as this and got round it using this hack:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

import java.util.concurrent.CountDownLatch;

public class StartUpTest extends Application {
    public static final CountDownLatch latch = new CountDownLatch(1);
    public static StartUpTest startUpTest = null;

    public static StartUpTest waitForStartUpTest() {
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return startUpTest;
    }

    public static void setStartUpTest(StartUpTest startUpTest0) {
        startUpTest = startUpTest0;
        latch.countDown();
    }

    public StartUpTest() {
        setStartUpTest(this);
    }

    public void printSomething() {
        System.out.println("You called a method on the application");
    }

    @Override
    public void start(Stage stage) throws Exception {
        BorderPane pane = new BorderPane();
        Scene scene = new Scene(pane, 500, 500);
        stage.setScene(scene);

        Label label = new Label("Hello");
        pane.setCenter(label);

        stage.show();
    }

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

and then the class you are launching the application from:

public class StartUpStartUpTest {
    public static void main(String[] args) {
        new Thread() {
            @Override
            public void run() {
                javafx.application.Application.launch(StartUpTest.class);
            }
        }.start();
        StartUpTest startUpTest = StartUpTest.waitForStartUpTest();
        startUpTest.printSomething();
    }
}

Hope that helps you.

I'm not sure what you're trying to achieve, but note that you can e.g call from another class Application.launch to start the JavaFX Application thread and Platform.exit to stop it.

The above ways of invoking other javafx class from another sometimes work. Struggling to find an ultimate way to do this brought me to the following walk around:

Suppose this is the javafx class that exteds Application we wish to show from a different class, then we should add the following lines

class ClassToCall extends Application{

  //Create a class field of type Shape preferably static...

  static Stage classStage = new Stage();

  @Override
  public void start(Stage primaryStage){

  // Assign the class's stage object to 
  // the method's local Stage object:

   classStage = primaryStage ;

  // Here comes some more code that creates a nice GUI.....
   // ......
  } 

}

And now from the other place in the project, in order to open the window that the above class creates do the following:

    // Suppose we want to do it with a button clicked:

    btn1.setOnAction(new EventHandler<ActionEvent>() {
        @Override
        public void handle(ActionEvent event) {

           //create an object of the class you wish to invoke its   
            //start() method:

            ClassToCall ctc = new ClassToCall();

          // Then call its start() method in the following way:

            ctc.start(ClassToCall.classStage);


       }// End handle(ActionEvent event)
     });// End anonymous class

Launch JavaFX in other Class using Button:

class Main extends Application{
 public void start(Stage s)throws Exception{
  event();
  s.show();
 }
 public void event(){
  btn.setOnAction(new EventHandler<ActionEvent>(){
   public void handle(ActionEvent ae){

    Stage s = new Stage();
    new SubClassName().start(s);

   }
  });

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

        launch(args);

}
}

class SubClassName{
 public void start(Stage s){

  Pane pane = new Pane();
  Scene addFrame = new Scene(pane,280,450);

  s.setScene(addFrame);     
  s.show();

 }

}