help with a code package application; import javafx.application.Application; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.geometry.Pos; import javafx.stage.Stage;...

help with a code

package application;


import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;

public class Main extends Application {
private CirclePane circlePane=new CirclePane();
@Override
public void start(Stage primaryStage) {
//holds two bottoms in an HBox
HBox hBox=new HBox();
hBox.setSpacing(10);
hBox.setAlignment(Pos.CENTER);
Button btEnlarge = new Button("Enlarge");
Button btShrink = new Button("Shrink");
hBox.getChildren().add(btEnlarge);
hBox.getChildren().add(btShrink);


//create and register the handler
btEnlarge.setOnAction(new EnlargeHandler());
btShrink.setOnAction(new ShrinkHandler());


BorderPane borderPane=new BorderPane();
borderPane.setCenter(circlePane);
borderPane.setBottom(hBox);
BorderPane.setAlignment(hBox,Pos.CENTER);


//create a scene and place it on the stage
Scene scene =new Scene(borderPane,200,150);
primaryStage.setTitle("Control Circle");
primaryStage.setScene(scene);
primaryStage.show();
}
class EnlargeHandler implements EventHandler{
@Override
public void handle(ActionEvent e) {
circlePane.enlarge();
}
}
class ShrinkHandler implements EventHandler{
@Override
public void handle(ActionEvent e) {
circlePane.shrink();
}
}
}


class CirclePane extends StackPane{
private Circle circle = new Circle();


public CirclePane() {
getChildren().add(circle);
circle.setStroke(Color.BLACK);
circle.setFill(Color.WHITE);
}
public void enlarge() {
circle.setRadius(circle.getRadius()+2);
}
public void shrink() {
circle.setRadius(circle.getRadius()>2?
circle.getRadius()-2 :circle.getRadius());
}



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