Here you can find the source of join(Collection
public static String join(Collection<String> in, String joinS)
//package com.java2s; /************************************************************************* * Copyright 2012 Regents of the University of Michigan * /* w w w . j a v a 2s. c o m*/ * NCIBI - The National Center for Integrative Biomedical Informatics (NCIBI) * http://www.ncib.org. * * This product may includes software developed by others; in that case see specific notes in the code. * * 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 3 of the License, or (at your option) any later version, along with the following terms: * 1. You may convey a work based on this program in accordance with section 5, * provided that you retain the above notices. * 2. You may convey verbatim copies of this program code as you receive it, * in any medium, provided that you retain the above notices. * * 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, http://www.gnu.org/licenses/. * * This work was supported in part by National Institutes of Health Grant #U54DA021519 * ******************************************************************/ import java.util.Collection; public class Main { public static String join(Collection<String> in, String joinS) { String ret = null; for (String s : in) { if (ret == null) ret = s; else ret += joinS + s; } if (ret == null) ret = ""; return ret; } }