如何正确实现按钮

Question

该程序首先显示由三个不同大小的cirlces创建的靶心。 单击animate me按钮（btn）后，函数animation（）将使现有圆圈向内缩小，直到cirlces的大小为零。将在先前存在的圆圈后面创建新的圆圈，这些圆圈正在向零收缩。新的圆圈也将趋于零。此过程将继续，直到用户再次点击动画我按钮。

在这个片段中，我有一个过程，可以在已经存在于屏幕上的预先存在的圆圈之后创建新按钮。在已经创建的新圈子之后，已经缩小到零的圈​​子将被重复使用以保持循环：

public class Target extends Application 
{
    Circle[] cir = new Circle[7];
    Button btn = new Button("Animate me!");
    StackPane root = new StackPane();

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

    /** 
     * @param primaryStage will create the target and the start button first 
     *        displayed onscreen to the user 
     */
    @Override
    public void start(Stage primaryStage) 
    {
        root.setStyle("-fx-border-color:black;");      

        cir[0] = new Circle(400, 250, 200);
        cir[0].setFill(Color.RED);
        cir[0].setStyle("-fx-border-color:black;");

        cir[1] = new Circle(315, 165, 115);
        cir[1].setFill(Color.WHITE);
        cir[1].setStyle("-fx-border-color:black;");

        cir[2] = new Circle(230, 80, 30);
        cir[2].setFill(Color.RED);
        cir[2].setStyle("-fx-border-color:black;");

        root.getChildren().addAll(cir[0], cir[1], cir[2]);      
        root.getChildren().add(btn);      

        primaryStage.setScene(new Scene(root));
        primaryStage.show();

        btn.setOnAction(e ->
        {
            animation();
            btn.setText("Press to Stop");
        });
    }

    public void animation()
    {
        ScaleTransition[] st = new ScaleTransition[7];
        boolean recycleCircles = false;


        st[0]= new ScaleTransition(Duration.seconds(7), cir[0]);
        st[0].setToX(0.0f);
        st[0].setToY(0.0f);
        st[0].play();

        st[1] = new ScaleTransition(Duration.seconds(5.5), cir[1]);
        st[1].setToX(0.0f);
        st[1].setToY(0.0f);
        st[1].play();

        st[2] = new ScaleTransition(Duration.seconds(4), cir[2]);
        st[2].setToX(0.0f);
        st[2].setToY(0.0f);
        st[2].play();

       // int delayInc = 1;
        int delay = 1;

        //will create circles (will rotate between white and red) and then add 
        //to scaleTransitions
        while(btn.isPressed() == false)
        {
            for(int i = 3; i<st.length; i++)
            {     
                if(recycleCircles == true)
                {
                    i = 0;
                    recycleCircles = false;
                }
                if(i % 2 == 1)
                {
                    cir[i] = new Circle(400,250,200);
                    cir[i].setFill(Color.WHITE);
                    cir[i].setStyle("-fx-border-color:black;");
                    root.getChildren().add(cir[i]);
                    cir[i].toBack();

                    st[i] = new ScaleTransition(Duration.seconds(7), cir[i]);
                    st[i].setDelay(Duration.seconds(delay));
                    delay++;
                    st[i].setToX(0.0f);
                    st[i].setToY(0.0f);
                    st[i].play();

                }

                else if(i%2==0)
                {
                    cir[i] = new Circle(400, 250, 200);
                    cir[i].setFill(Color.RED);
                    cir[i].setStyle("-fx-border-color:black;");
                    root.getChildren().add(cir[i]);
                    cir[i].toBack();

                    st[i] = new ScaleTransition(Duration.seconds(7), cir[i]);
                    st[i].setDelay(Duration.seconds(delay));
                    delay++;
                    st[i].setToX(0.0f);
                    st[i].setToY(0.0f);
                    st[i].play();

                }

                if(i == 6)
                    recycleCircles = true;
            }
        }

        btn.setOnMousePressed(event ->
        {



        });   

        btn.setOnMouseReleased(event -> 
        {
            for(int y = 0; y<st.length;y++)
            {

            }
        });


    }  
}