java - 即使声明为最终边界也会更新

Question

我正在尝试制作一个带有球的程序，这些球(首先)在靠近屏幕边界时会弹起。

但是，当检查bounds.getmaxY()值时，我可以看到该值正在增加，并且我猜是因为if循环从未被使用过。

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 变量根本没有改变，您只是每次都会获得它的一个新实例。

我认为这里发生的情况是，您在查询 Pane 的边界之前更改了球的布局。 Pane 不断增大以适应球位置的变化。所以尝试一下

                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);