snippet to find angle between 2 points - working on GRAPHICAL CANVAS

public static void GetAngleOfLineBetweenTwoPoints(Point2D p1, Point2D p2)
    {
          double deltaY = p1.getY() - p2.getY() ;
          double deltaX = p2.getX() - p1.getX() ;

            double angleInDegrees = Math.toDegrees(Math.atan(deltaY / deltaX)) ; // * 180 / Math.PI ;
            double angleInDegrees2 = Math.toDegrees(Math.atan2(deltaY, deltaX)) ;// * 180 / Math.PI ;
            System.out.println( " angle using atan\t" + angleInDegrees ) ;
            System.out.println( " angle using atan2\t" + angleInDegrees2 ) ;
          /*
        double xDiff = p2.getX() - p1.getX() ;
        double yDiff = p2.getY() - p1.getY() ;
        return Math.toDegrees(Math.atan2(yDiff, xDiff));
        */
    }