Here you can find the source of join(String[]... values)
public static String[] join(String[]... values)
//package com.java2s; import java.util.ArrayList; import java.util.Collections; import java.util.List; public class Main { public static String[] join(String[]... values) { List<String> list = new ArrayList<String>(); for (String[] strings : values) Collections.addAll(list, strings); return list.toArray(new String[list.size()]); }//from www . j ava 2 s. com }