Here you can find the source of angle(Point2D from, Point2D to)
public static double angle(Point2D from, Point2D to)
//package com.java2s; /* /*from w ww. ja v a2 s .c o m*/ Created on Mar 4, 2005 The Bungee View applet lets you search, browse, and data-mine an image collection. Copyright (C) 2006 Mark Derthick This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. See gpl.html. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. You may also contact the author at mad@cs.cmu.edu, or at Mark Derthick Carnegie-Mellon University Human-Computer Interaction Institute Pittsburgh, PA 15213 */ import java.awt.geom.Point2D; public class Main { public static double angle(Point2D from, Point2D to) { Point2D delta = subtract(from, to); return Math.atan2(delta.getY(), delta.getX()); } public static Point2D subtract(Point2D from, Point2D to) { return new Point2D.Double(to.getX() - from.getX(), to.getY() - from.getY()); } }