JavaFX MouseEvent drag vertices of a triangle

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.shape.Polygon;
import javafx.scene.shape.Circle;
import javafx.scene.text.Text;
import javafx.scene.paint.Color;
import javafx.collections.ObservableList;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
import java.util.ArrayList;

public class Main extends Application {
   @Override//from  w ww.j a v  a2 s  .c  om
   public void start(Stage primaryStage) {
      Pane pane = new Pane();

      // Create three points and add them to a list
      Circle p1 = new Circle(50, 100, 5);
      Circle p2 = new Circle(100, 25, 5);
      Circle p3 = new Circle(150, 80, 5);
      ArrayList<Circle> points = new ArrayList<>();
      points.add(p1);
      points.add(p2);
      points.add(p3);

      // Place nodes in the pane
      drawTriangle(pane, points);
      pane.getChildren().addAll(p1, p2, p3);
      placeText(pane, points);

      // Create and register the handle
      pane.setOnMouseDragged(e -> {
         for (int i = 0; i < points.size(); i++) {
            if (points.get(i).contains(e.getX(), e.getY())) {
               pane.getChildren().clear();
               points.get(i).setCenterX(e.getX());
               points.get(i).setCenterY(e.getY());
               drawTriangle(pane, points);
               pane.getChildren().addAll(p1, p2, p3);
               placeText(pane, points);
            }
         }
      });         

      // Create a scene and place it in the stage
      Scene scene = new Scene(pane, 200, 200);
      primaryStage.setTitle("java2s.com");
      primaryStage.setScene(scene);
      primaryStage.show();
   }

   /** Adds three angles to the pane */
   private void placeText(Pane pane, ArrayList<Circle> p) {
      double[] sides = getSides(p);
      double[] angles = getAngles(sides);
      pane.getChildren().add(new Text(p.get(0).getCenterX(),
         p.get(0).getCenterY() - 5, String.format("%.2f", angles[0])));
      pane.getChildren().add(new Text(p.get(1).getCenterX(), 
         p.get(1).getCenterY() - 5, String.format("%.2f", angles[1])));
      pane.getChildren().add(new Text(p.get(2).getCenterX(), 
         p.get(2).getCenterY() - 5, String.format("%.2f", angles[2])));
   }

   /** Calculates and returns an array of sides in a triangle */
   private double[] getSides(ArrayList<Circle> p) {
      double[] sides = new double[3];
      sides[0] = Math.sqrt(Math.pow(p.get(0).getCenterX() - 
         p.get(1).getCenterX(), 2) + Math.pow(p.get(0).getCenterY() - 
         p.get(1).getCenterY(), 2));
      sides[1] = Math.sqrt(Math.pow(p.get(1).getCenterX() - 
         p.get(2).getCenterX(), 2) + Math.pow(p.get(1).getCenterY() - 
         p.get(2).getCenterY(), 2));
      sides[2] = Math.sqrt(Math.pow(p.get(2).getCenterX() - 
         p.get(0).getCenterX(), 2) + Math.pow(p.get(2).getCenterY() - 
         p.get(0).getCenterY(), 2));
      return sides;
   }

   /** Calculates and returns an array of angles in a triangle */
   private double[] getAngles(double[] s) {
      double[] angles = new double[3];
      angles[0] = Math.toDegrees(Math.acos((s[0] * s[0] - s[1] * 
         s[1] - s[2] * s[2]) / (-2 * s[1] * s[2])));
      angles[1] = Math.toDegrees(Math.acos((s[1] * s[1] - s[0] * 
         s[0] - s[2] * s[2]) / (-2 * s[0] * s[2])));
      angles[2] = Math.toDegrees(Math.acos((s[2] * s[2] - s[1] * 
         s[1] - s[0] * s[0]) / (-2 * s[0] * s[1])));
      return angles;
   }

   /** Create a polygon */
   private void drawTriangle(Pane pane, ArrayList<Circle> p) {
      Polygon polygon = new Polygon();
      pane.getChildren().add(polygon);
      ObservableList<Double> points = polygon.getPoints();
      for (int i = 0; i < p.size(); i++) {
         points.add(p.get(i).getCenterX());
         points.add(p.get(i).getCenterY());
      }
      polygon.setFill(Color.WHITE);
      polygon.setStroke(Color.BLACK);
   }  public static void main(String[] args) {
      launch(args);
   }
}