问JavaFX代码gui不执行代码建议的操作

EN

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Ellipse;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class OlympicRings extends Application {

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

    @Override
    public void start(Stage

    primaryStage) {
        primaryStage.setTitle("Olympic Rings");

        StackPane root = new StackPane();

        // create 5 ellipses
        Ellipse e1 = new Ellipse(60, 40);
        e1.setFill(Color.BLUE);
        e1.setStroke(Color.BLACK);
        e1.setStrokeWidth(2);

        Ellipse e2 = new Ellipse(80, 50);
        e2.setFill(Color.YELLOW);
        e2.setStroke(Color.BLACK);
        e2.setStrokeWidth(2);

        Ellipse e3 = new Ellipse(100, 60);
        e3.setFill(Color.BLACK);
        e3.setStroke(Color.BLACK);
        e3.setStrokeWidth(2);

        Ellipse e4 = new Ellipse(120, 70);
        e4.setFill(Color.GREEN);
        e4.setStroke(Color.BLACK);
        e4.setStrokeWidth(2);

        Ellipse e5 = new Ellipse(140, 80);
        e5.setFill(Color.RED);
        e5.setStroke(Color.BLACK);
        e5.setStrokeWidth(2);

        // create 5 rectangles
        Rectangle r1 = new Rectangle(60, 20);
        r1.setFill(Color.BLUE);
        r1.setStroke(Color.BLACK);
        r1.setStrokeWidth(2);

        Rectangle r2 = new Rectangle(80, 30);
        r2.setFill(Color.YELLOW);
        r2.setStroke(Color.BLACK);
        r2.setStrokeWidth(2);

        Rectangle r3 = new Rectangle(100, 40);
        r3.setFill(Color.BLACK);
        r3.setStroke(Color.BLACK);
        r3.setStrokeWidth(2);

        Rectangle r4 = new Rectangle(120, 50);
        r4.setFill(Color.GREEN);
        r4.setStroke(Color.BLACK);
        r4.setStrokeWidth(2);

        Rectangle r5 = new Rectangle(140, 60);
        r5.setFill(Color.RED);
        r5.setStroke(Color.BLACK);
        r5.setStrokeWidth(2);

        // create a text
        Text t = new Text("The Olympic Rings");
        t.setStyle("-fx-font-size: 16px;");

        // put all the shapes together
        root.getChildren().addAll(e1, e2, e3, e4, e5, r1, r2, r3, r4, r5, t);

        // create a scene
        Scene scene = new Scene(root, 600, 400);

        // set the scene on the stage
        primaryStage.setScene(scene);

        // show the stage
        primaryStage.show();
    }
}