Here you can find the source of union(Collection firstSet, Collection secondSet)
public static Collection union(Collection firstSet, Collection secondSet)
//package com.java2s; /*L//from ww w.j a va 2 s . c o m * Copyright Ekagra Software Technologies Ltd. * Copyright SAIC, SAIC-Frederick * * Distributed under the OSI-approved BSD 3-Clause License. * See http://ncip.github.com/common-security-module/LICENSE.txt for details. */ import java.util.*; public class Main { public static Collection union(Collection firstSet, Collection secondSet) { return null; } }