Sure, here is a simple “Hello, World!” program written in JavaFX. It simply creates a small window that says “Hello, World!”:

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

public class HelloWorld extends Application {

    @Override
    public void start(Stage primaryStage) {
        Label helloWorldLabel = new Label("Hello, World!");
        Scene scene = new Scene(helloWorldLabel, 200, 100);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

}

Now, let’s break it down:

1. Import Statements: These lines import the necessary classes from the JavaFX library that will be used in this program.

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

2. Class Declaration: This line declares a new public class called HelloWorld that extends the Application class. The Application class is part of JavaFX and serves as the base class for creating desktop applications.

public class HelloWorld extends Application {

3. Start Method: This is the main entry point for all JavaFX applications. It is called when the program is launched. The Stage object, primaryStage, is the main top-level container.

@Override
public void start(Stage primaryStage) {

4. Label Creation: This line creates a new Label object, helloWorldLabel, and sets its text to “Hello, World!”.

Label helloWorldLabel = new Label("Hello, World!");

5. Scene Creation: This line creates a new Scene object, scene, adds helloWorldLabel to it, and sets its width to 200 pixels and its height to 100 pixels.

Scene scene = new Scene(helloWorldLabel, 200, 100);

6. Setting the Scene: This line sets the primaryStage’s scene to scene.

primaryStage.setScene(scene);

7. Displaying the Stage: This line shows the primaryStage, which makes the GUI visible.

primaryStage.show();

8. Main Method: This is the entry point for the Java program and is the first method that gets executed when the program starts. It calls the launch method, which then calls the start method.

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