JavaFX Circle drag and drop to move

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class Main extends Application {
   @Override//from  w  w  w.j  a va  2  s . co m
   public void start(Stage primaryStage) {
      final double WIDTH = 500.0;
      final double HEIGHT = 500.0;
      final double RADIUS = 10.0;

      Circle c1 = new Circle(40, 40, RADIUS);
      c1.setFill(Color.WHITE);
      c1.setStroke(Color.BLACK);
      Circle c2 = new Circle(120, 150, RADIUS);
      c2.setFill(Color.WHITE);
      c2.setStroke(Color.BLACK);

      Line line = new Line(c1.getCenterX(), c1.getCenterY(), c2.getCenterX(), c2.getCenterY());
      line.startXProperty().bind(c1.centerXProperty());
      line.startYProperty().bind(c1.centerYProperty());
      line.endXProperty().bind(c2.centerXProperty());
      line.endYProperty().bind(c2.centerYProperty());

      Text text = new Text(getMidX(line), getMidY(line), String.valueOf(distance(line)));

      Pane pane = new Pane();
      pane.getChildren().addAll(line, text, c1, c2);

      EventHandler<MouseEvent> dragCircle = e -> {
         ((Circle) e.getSource()).setCenterX(e.getX());
         ((Circle) e.getSource()).setCenterY(e.getY());
         text.setX(getMidX(line));
         text.setY(getMidY(line));
         text.setText(String.valueOf(distance(line)));
      };

      c1.setOnMouseDragged(dragCircle);
      c2.setOnMouseDragged(dragCircle);

      Scene scene = new Scene(pane, WIDTH, HEIGHT);
      primaryStage.setTitle("java2s.com");
      primaryStage.setScene(scene);
      primaryStage.show();
   }

   public static double distance(Line line) {
      double x1 = line.getStartX();
      double y1 = line.getStartY();
      double x2 = line.getEndX();
      double y2 = line.getEndY();
      return Math.sqrt(Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2));
   }

   public static double getMidX(Line line) {
      return (line.getStartX() + line.getEndX()) / 2;
   }

   public static double getMidY(Line line) {
      return (line.getStartY() + line.getEndY()) / 2;
   }

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