如何使用JavaFX将可移动对象保留在窗口内？

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class Main extends Application {

    private static final int WINDOW_WIDTH = 800;
    private static final int WINDOW_HEIGHT = 600;
    private static final int RECTANGLE_SIZE = 50;

    @Override
    public void start(Stage primaryStage) {
        // 创建可移动对象
        Rectangle rectangle = new Rectangle(RECTANGLE_SIZE, RECTANGLE_SIZE);

        // 添加可移动对象到场景
        Pane root = new Pane(rectangle);
        Scene scene = new Scene(root, WINDOW_WIDTH, WINDOW_HEIGHT);

        // 处理键盘事件
        scene.setOnKeyPressed(event -> {
            KeyCode keyCode = event.getCode();
            double x = rectangle.getX();
            double y = rectangle.getY();

            // 根据按下的键盘按键来移动可移动对象的位置
            switch (keyCode) {
                case UP:
                    if (y > 0) {
                        rectangle.setY(y - 10);
                    }
                    break;
                case DOWN:
                    if (y < WINDOW_HEIGHT - RECTANGLE_SIZE) {
                        rectangle.setY(y + 10);
                    }
                    break;
                case LEFT:
                    if (x > 0) {
                        rectangle.setX(x - 10);
                    }
                    break;
                case RIGHT:
                    if (x < WINDOW_WIDTH - RECTANGLE_SIZE) {
                        rectangle.setX(x + 10);
                    }
                    break;
            }
        });

        // 设置窗口属性
        primaryStage.setTitle("Moving Object");
        primaryStage.setScene(scene);
        primaryStage.setResizable(false);
        primaryStage.show();
    }

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