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[英]My Face class does not seem to be immutable even though I already declared it as final, how do I correct it?
[英]Bounds updating even though declared as final
我正在嘗試制作一個程序,它的球在接近屏幕邊界時會(首先)反彈。
但是,當檢查bounds.getmaxY()值時,我可以看到該值正在增加,並且由於我猜想從來沒有使用過if循環。
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();
}
});
}
您的Bounds
變量根本沒有改變,您每次都只獲得一個新實例。
我認為這里發生的事情是,您在查詢窗格的邊界之前更改了球的布局。 窗格正在增長以適應球位置的變化。 所以嘗試
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);
將值聲明為final不會使對象不變。 這僅表示對對象的引用將不會更改-即,每次引用bounds
,您將獲得相同的對象。 一旦賦值,最終變量就不能更改為指向另一個Bounds
對象。
不能分配最終變量,但是您可以更改它的屬性,因為您不會使其不可變。
看一下有關定義不可變對象的文章 。
在您的情況下,如果可以訪問Bounds對象,則可以使用此解決方案來實現它,但是如果您不能修改Bounds對象以使其不可變,則需要為Bounds編寫包裝類。
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