Here you can find the source of addAll(List dest, List src)
public static List addAll(List dest, List src)
//package com.java2s; /*//from w ww . j av a 2s . c o m Jazzy - a Java library for Spell Checking Copyright (C) 2001 Mindaugas Idzelis Full text of license can be found in LICENSE.txt This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library 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 Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ import java.util.Iterator; import java.util.List; public class Main { public static List addAll(List dest, List src) { return addAll(dest, src, true); } public static List addAll(List dest, List src, boolean allow_duplicates) { for (Iterator e = src.iterator(); e.hasNext();) { Object o = e.next(); if (allow_duplicates || !dest.contains(o)) dest.add(o); } return dest; } }