JavaFX Line draw arrow from random start to random end

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Line;
import javafx.stage.Stage;

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

      double paneWidth = 300;
      double paneHeight = 250;
      double x1 = Math.random() * (paneWidth - 12);
      double y1 = Math.random() * (paneHeight - 12);
      double x2 = Math.random() * (paneWidth - 12);
      double y2 = Math.random() * (paneHeight - 12);

      drawArrowLine(x1, y1, x2, y2, pane);

      Scene scene = new Scene(pane, 400, 250);
      primaryStage.setTitle("java2s.com");
      primaryStage.setScene(scene);
      primaryStage.show();
   }

   public static void drawArrowLine(double x1, double y1, double x2, double y2, Pane pane) {
      pane.getChildren().add(new Line(x1, y1, x2, y2));

      // find slope of this line
      double slope = ((((double) y1) - (double) y2)) / (((double) x1) - (((double) x2)));

      double arctan = Math.atan(slope);

      double set45 = 1.57 / 2;

      if (x1 < x2) {
         // add 90 degrees to arrow lines
         set45 = -1.57 * 1.5;
      }

      int arrlen = 15;

      pane.getChildren().add(
            new Line(x2, y2, (x2 + (Math.cos(arctan + set45) * arrlen)), ((y2)) + (Math.sin(arctan + set45) * arrlen)));

      pane.getChildren().add(
            new Line(x2, y2, (x2 + (Math.cos(arctan - set45) * arrlen)), ((y2)) + (Math.sin(arctan - set45) * arrlen)));
   }

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