Here you can find the source of concat(List
static String[] concat(List<String>... lists)
//package com.java2s; //License from project: Apache License import java.util.List; import java.util.ArrayList; public class Main { static String[] concat(List<String>... lists) { List<String> c = new ArrayList<String>(); for (List<String> l : lists) { c.addAll(l);// ww w. j a va 2s. c om } return c.toArray(new String[c.size()]); } }