Objektorienteeritud programmeerimine (Narva Kolledž) 2017/18 kevad

Session 7

First graphic program

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

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

public class BlackSquare extends Application {

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

    @Override
    public void start(Stage primaryStage) {

    }
}

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 7) 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 11). The method's argument is an object of Stage type. A Stage type object (called primary stage) is a window which is automatically created by the JVM when the application is launched.

Supplement start method with some content.

    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 UI 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 into a 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