Question

我试图制作一个带有球的程序（首先）在关闭屏幕边框时反弹。

然而，当检查bounds.getmaxY（）值时，我可以看到该值正在增加，因为if-loops永远不会被使用。

public class bouncyFX extends Application {


public static void main(String[] args) {
    launch(args);
}
static Pane pane = new Pane();

@Override
public void start(final Stage primaryStage) {
    Scene scene = new Scene(pane, 500, 200);
    primaryStage.setScene(scene);
    primaryStage.show();
    pane.setOnMouseClicked(new EventHandler<MouseEvent>() {
        public void handle(final MouseEvent event) {
            final Ball ball = new Ball(event.getX(), event.getY(), 12, Color.AQUA);
            ball.relocate(event.getX(), event.getY());
            pane.getChildren().addAll(ball);
            final Timeline loop = new Timeline(new KeyFrame(Duration.millis(10), new EventHandler<ActionEvent>() {
                double deltaX = 2;
                double deltaY = 2;
                public void handle(final ActionEvent event) {
                    ball.setLayoutX(ball.getLayoutX() + deltaX);
                    ball.setLayoutY(ball.getLayoutY() + deltaY);
                    ball.Collision(deltaX, deltaY);

                    final Bounds bounds = pane.getBoundsInLocal();
                    final boolean atRightBorder = ball.getLayoutX() >= (bounds.getMaxX()-ball.getRadius());
                    final boolean atLeftBorder = ball.getLayoutX() <= (bounds.getMinX()+ball.getRadius());
                    final boolean atBottomBorder = ball.getLayoutY() >= (bounds.getMaxY()-ball.getRadius());
                    final boolean atTopBorder = ball.getLayoutY() <= (bounds.getMinY()+ball.getRadius());
                    if(atRightBorder || atLeftBorder)
                        deltaX *= -1;
                    if(atBottomBorder ||atTopBorder)
                        deltaY *= -1;
                }
            }));
            loop.setCycleCount(Timeline.INDEFINITE);
            loop.play();
        }
    });
}

Answer 1

您的Bounds变量根本没有变化，您每次都会得到一个新的实例。

我认为这里发生的事情是在查询窗格的边界之前更改球的布局。窗格正在增长，以适应球的位置变化。所以试试

                final Bounds bounds = pane.getBoundsInLocal();
                final boolean atRightBorder = ball.getLayoutX() + deltaX >= (bounds.getMaxX()-ball.getRadius());
                final boolean atLeftBorder = ball.getLayoutX() + deltaX <= (bounds.getMinX()+ball.getRadius());
                final boolean atBottomBorder = ball.getLayoutY() + deltaY >= (bounds.getMaxY()-ball.getRadius());
                final boolean atTopBorder = ball.getLayoutY() + deltaY <= (bounds.getMinY()+ball.getRadius());
                if(atRightBorder || atLeftBorder)
                    deltaX *= -1;
                if(atBottomBorder ||atTopBorder)
                    deltaY *= -1;

                ball.setLayoutX(ball.getLayoutX() + deltaX);
                ball.setLayoutY(ball.getLayoutY() + deltaY);

                // not sure what this line does, so you will need to put it where it makes sense:
                ball.Collision(deltaX, deltaY);

Answer 2

将值声明为final不会使对象不可变。它只是意味着对对象的引用不会改变 - 即每次引用bounds时，您将获得相同的对象。分配后，无法将最终变量更改为指向另一个Bounds对象。

Answer 3

无法分配最终变量，但您可以更改它的属性，因为您没有将其变为不可变。

看一下关于定义不可变对象的this article。

在您的情况下，如果您可以访问Bounds对象，则可以使用此解决方案来实现它，但如果您无法修改Bounds对象以使其成为不可变，则需要为Bounds编写包装类。

即使声明为final，也会更新边界

3 个答案: