Main.java

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import java.util.ArrayList;

public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        ArrayList<CreateRect> rects = new ArrayList<>();
        Group root = new Group();
        Scene scene = new Scene(root, 300, 250);

        CreateRect rectangle = new CreateRect(50, 50, 200, 100);
        rects.add(rectangle);

        for (Rectangle rect : rects) {
            root.getChildren().add(rect);
        }
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}