Here you can find the source of union(List ls, List ls2)
@SuppressWarnings({ "unchecked", "rawtypes" })
public static <T> List<T> union(List ls, List ls2)
//package com.java2s; /**/*w w w . j a va2 s . c om*/ * MIT License * * Copyright (c) 2017 CaiDongyu * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all * copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. */ import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class Main { @SuppressWarnings({ "unchecked", "rawtypes" }) public static <T> List<T> union(List ls, List ls2) { List list = new ArrayList(Arrays.asList(new Object[ls.size()])); Collections.copy(list, ls); list.addAll(ls2); return list; } }