Here you can find the source of angle(double aX, double aY, double bX, double bY)
public static double angle(double aX, double aY, double bX, double bY)
//package com.java2s; /*/*from ww w . j av a2s.co m*/ * The MIT License * * Copyright 2014 emerson. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ public class Main { public static double angle(double aX, double aY, double bX, double bY) { double deltaX = bX - aX; double deltaY = bY - aY; if (deltaX == 0) { return 90; } if (deltaY == 0) { return 0; } double tang = deltaY / deltaX; double tangRad = Math.atan(tang); double tangGrau = tangRad * 36 / 2 * Math.PI; return tangGrau; } }