Object-Oriented Programming (Narva College) 2018/19 spring

Session 7

First graphic program

Let's start with a new class called BlackBox: File -> New -> JavaFXApplication. Here is the code:

import javafx.application.Application;
import javafx.stage.Stage;

public class BlackBox extends Application {

    @Override
    public void start(Stage primaryStage) {

    }

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

}

Every JavaFX program has to be defined in a class that extends javafx.application.Application. The program starts its work from the main method, as usually.

• launch method (line 12) is a static method defined in Application class for launching a stand-alone JavaFX application.
• The main class overrides start method defined in Application class (line 7). The method's argument is an object of Stage type. A Stage type object (called primaryStage) is a window which is automatically created by the JVM when the application is launched.

Add the following content to the start method:

    public void start(Stage primaryStage) {
        Group root = new Group(); // create a root node
        Rectangle rectangle1 = new Rectangle(50, 50, 435, 435);
        root.getChildren().add(rectangle1);  // place the rectangle onto the scene
        Scene scene1 = new Scene(root, 535, 535, Color.SNOW);  // create the scene
        primaryStage.setTitle("Black square");  // set a title for the stage
        primaryStage.setScene(scene1);  // place the scene onto the stage
        primaryStage.show();  // display the stage
    }

The method start normally places shapes and controls on the scene, and also displays the scene on the stage, as shown below:

Line 2 creates a Group type object that acts as a root. A Rectangle type object is a shape that we would like to see. Line 4 places the rectangle onto the Scene type object. The Scene type object is created using the constructor Scene(root, width, height, color). This constructor specifies the color, width and height of the scene and places the root on the scene. Finally, we place the scene onto the stage (Line 7).

JavaFX names Stage and Scene classes using an analogy with the theatre. We can assume that the stage is a platform which supports scenes, and in each scene there are actors(shapes) who perform in the scenes.

Session 7