Here you can find the source of join(Collection
public static String join(Collection<String> src, String delim)
//package com.java2s; /*/*from w w w . j av a 2 s. c om*/ * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ import java.util.*; public class Main { public static String join(Collection<String> src, String delim) { StringBuilder sb = new StringBuilder(); boolean first = true; for (String s : src) { if (first) { first = false; } else { sb.append(delim); } sb.append(s); } return sb.toString(); } public static String join(String[] src, String delim) { return join(Arrays.asList(src), delim); } }