题目：编写一个程序，在面板上移动小球。应该定义一个面板类来显示小球，并提供向上下左右移动小球的方法。请进行边界检查以防止小球移动到视线之外。
问题：我写的程序可以运行但是无法显示小球的移动，如果将移动改为改变小球颜色则可以显示，检查许久也检查不到问题在哪，所以贴上来问问大佬们，问题出在哪里？应该如何改？
代码如下：
public class MoveBall_3 extends Application{
private CirclePane circlePane = new CirclePane(250,250);
public static void main(String[] args) {
Application.launch(args);
}
public void start(Stage primaryStage) throws Exception {
Button bt1 = new Button("Left");
Button bt2 = new Button("Right");
Button bt3 = new Button("Up");
Button bt4 = new Button("Down");
bt1.setOnAction(new EventHandler<ActionEvent>(){
@Override
public void handle(ActionEvent event) {
// TODO 自动生成的方法存根
circlePane.moveLeft();
}
});
bt2.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
// TODO 自动生成的方法存根
circlePane.moveRight();
}
});
bt3.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
// TODO 自动生成的方法存根
circlePane.moveUp();
}
});
bt4.setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
// TODO 自动生成的方法存根
circlePane.moveDown();
}
});
FlowPane pane2 = new FlowPane();
pane2.getChildren().addAll(bt1,bt2,bt3,bt4);
circlePane.getChildren().addAll(pane2);
Scene scene = new Scene(circlePane,500,500);
primaryStage.setTitle("MoveBall");
primaryStage.setScene(scene);
primaryStage.show();
}
}
class CirclePane extends StackPane{
private Circle circle = new Circle(250,250,50);
public CirclePane() {
getChildren().add(circle);
circle.setStroke(Color.BLACK);
circle.setFill(Color.WHITE);
}
public CirclePane(double a,double b) {
getChildren().add(circle);
circle.setCenterX(a);
circle.setCenterY(b);
circle.setStroke(Color.BLACK);
circle.setFill(Color.WHITE);
}
public void moveLeft() {
if(circle.getCenterX()-50-15 >= 0) {
circle.setCenterX(circle.getCenterX()-15);
circle.setCenterY(circle.getCenterY());
}
else {
circle.setCenterX(50);
circle.setCenterY(circle.getCenterY());
}
}
public void moveRight() {
if(circle.getCenterX()+50+15 <= 500) {
circle.setCenterX(circle.getCenterX()+15);
circle.setCenterY(circle.getCenterY());
}
else {
circle.setCenterX(450);
circle.setCenterY(circle.getCenterY());
}
}
public void moveUp() {
if(circle.getCenterY()-50-15 >= 0) {
circle.setCenterY(circle.getCenterY()-15);
circle.setCenterX(circle.getCenterX());
}
else {
circle.setCenterY(50);
circle.setCenterX(circle.getCenterX());
}
}
public void moveDown() {
if(circle.getCenterY()+50+15 <= 500) {
circle.setCenterY(circle.getCenterY()+15);
circle.setCenterX(circle.getCenterX());
}
else {
circle.setCenterY(450);
circle.setCenterX(circle.getCenterX());
}
}
}
