Here you can find the source of concat(Collection
public static <T> List<T> concat(Collection<T> list1, Collection<T> list2)
//package com.java2s; //License from project: Open Source License import java.util.ArrayList; import java.util.Collection; import java.util.List; public class Main { public static <T> List<T> concat(Collection<T> list1, Collection<T> list2) { List<T> result = new ArrayList<>(list1); result.addAll(list2);//from w w w . j a va2s . co m return result; } }