I'll try to demonstrate some different approaches for passing a reference between a java program, and a java-fx program.
I post it in hope it will help some future readers having similar need. I also hope it may encourage other answers with additional solutions.
The posted code should not be considered proper implementation, but rather a short code aiming to clarify the different approaches. For this purpose I'll introduce a simple listening interface :
interface Observe{ void update(int i); }
A java class, that represents an exiting business application :
public class JavaApp {
private Observe observer; private int counter = 0;
JavaApp(Observe observer){ //not null safe
this.observer = observer;
}
void process() {
new Timer().scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
observer.update(counter >=100 ? 0 : ++counter);
}
}, 1000,1000);
}
}
A java-fx application that should be added to the existing business application, listen to it and serve as view:
public class JavaFxApp extends Application implements Observe{
private Label label;
@Override public void start(Stage stage) {
label = new Label("waiting");
BorderPane pane = new BorderPane(label);
Scene scene = new Scene(pane, 100, 100);
stage.setScene(scene);
stage.show();
}
@Override public void update(int i) {
Platform.runLater(()-> label.setText(String.valueOf(i)));
}
}
How do we share a reference, in this case a reference to Observe instance, between the two applications ?
Approach 1: Consider the start() method as the entry point to the application (see James_D answer)
This is simple and straight forward if you want to tie the existing java application with java-fx and use java-fx Application as the entry point:
public class JavaFxApp extends Application implements Observe{
private Label label;
@Override public void start(Stage stage) {
JavaApp main = new JavaApp(this);
label = new Label("waiting");
BorderPane pane = new BorderPane(label);
Scene scene = new Scene(pane, 100, 100);
stage.setScene(scene);
stage.show();
new Thread(()-> { main.process();}).start(); //launch the business process
}
@Override public void update(int i) {
Platform.runLater(()-> label.setText(String.valueOf(i)));
}
public static void main(String[] args) { launch(); }
}
Approach 2: Use JavaFX 9 Platform#startup
This is the best solution I found, when you can not use the Application#start method as the entry point to the application.
As demonstrated in fabians answer, as off java-fx 9 you can launch without extending Application. All you have to do is modify the main of the java application:
public class JavaApp {
private Observe observer; private int counter = 0;
JavaApp(Observe observer){//not null safe
this.observer = observer;
}
void process() {
new Timer().scheduleAtFixedRate(new TimerTask() {
@Override public void run() {
observer.update(counter >=100 ? 0 : ++counter);
}
}, 1000,1000);
}
public static void main(String[] args) {
JavaFxApp view = new JavaFxApp(); //initialize JavaFx application
JavaApp main = new JavaApp(view);
Platform.startup(() -> {//launch JavaFx application
Stage stage = new Stage();
try {
view.start(stage);
} catch (Exception ex) {ex.printStackTrace();}
});
main.process(); //run business process
}
}
Approach 3: Use Static members
For example introduce a static getter in the java-fx application :
public class JavaFxApp extends Application {
private static Label label = new Label("waiting");
@Override public void start(Stage stage) {
BorderPane pane = new BorderPane(label);
Scene scene = new Scene(pane, 100, 100);
stage.setScene(scene);
stage.show();
}
static Observe getObserver() {
return JavaFxApp::update;
}
private static void update(int i) {
Platform.runLater(()-> label.setText(String.valueOf(i)));
}
}
and use it in the java application:
public class JavaApp {
private Observe observer; private int counter = 0;
JavaApp(Observe observer){//not null safe
this.observer = observer;
}
void process() {
new Timer().scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
observer.update(counter >=100 ? 0 : ++counter);
}
}, 1000,1000);
}
public static void main(String[] args){
new Thread(()-> Application.launch(JavaFxApp.class)).start();
Observe observer = JavaFxApp.getObserver(); //get static observer reference
JavaApp main = new JavaApp(observer);
main.process();
}
}
A better approach to get a static reference might be (based on this answer) :
public class JavaFxApp extends Application implements Observe{
private static final CountDownLatch latch = new CountDownLatch(1);
private static Observe observer = null;
private Label label;
@Override public void init() {
observer = this;
latch.countDown();
}
@Override public void start(Stage stage){
label = new Label("waiting");
BorderPane pane = new BorderPane(label);
Scene scene = new Scene(pane, 100, 100);
stage.setScene(scene);
stage.show();
}
@Override public void update(int i) {
Platform.runLater(()-> label.setText(String.valueOf(i)));
}
static Observe getObserver() {
try {
latch.await();
} catch (InterruptedException e) { e.printStackTrace(); }
return observer;
}
}
