Java去重合並List

之前寫C#的項目，去重合並List很方便，使用list1.Union(list2).ToList()即可(Enumerable.Union)。並且，如果想要從list1裏移除list2的item，也很方便，list2.Except(list1).ToList()

現在寫Java的項目，它沒有此類原生方法可以直接調用，操作起來，稍微多點步驟。

    public static void main(String[] args){
        List<String> listA = Arrays.asList("Unicorn","Penguin","Koala","Hippo","Unicorn");
        List<String> listB = Arrays.asList("Swan","Penguin","Ape");
        //Merge lists and remove duplicated entries
        Set<String> set = new LinkedHashSet<>();
        set.addAll(listA);
        set.addAll(listB);
        System.out.println("Merge and remove duplicates: " + set);
        //Intersection
        List<String> intersection = new ArrayList<>(listA);
        intersection.retainAll(listB);
        System.out.println("Intersection of two lists: " + intersection);
        //Concat
        List<String> concat = new ArrayList<>(listA);
        concat.addAll(listB);
        System.out.println("Concat of two lists: " + concat);
        //listA - listB
        List<String> minus = new ArrayList<>(listA);
        minus.removeAll(listB);
        System.out.println("Remove items that are in listB from listA: " + minus);
    }

程序輸出：
Merge and remove duplicates: [Unicorn, Penguin, Koala, Hippo, Swan, Ape]
Intersection of two lists: [Penguin]
Concat of two lists: [Unicorn, Penguin, Koala, Hippo, Unicorn, Swan, Penguin, Ape]
Remove items that are in listB from listA: [Unicorn, Koala, Hippo, Unicorn]