Steam list between two intersection, union, difference

public static void main(String[] args) {
    List<String> list1 = new ArrayList();
    list1.add("1111");
    list1.add("2222");
    list1.add("3333");

    List<String> list2 = new ArrayList();
    list2.add("3333");
    list2.add("4444");
    list2.add("5555");

    // 交集
    List<String> intersection = list1.stream().filter(item -> list2.contains(item)).collect(Collectors.toList());
    System.out.println("---得到交集 intersection---");
    intersection.parallelStream().forEach(System.out :: println);

    // 差集 (list1 - list2)
    List<String> reduce1 = list1.stream().filter(item -> !list2.contains(item)).collect(Collectors.toList());
    System.out.println("---得到差集 reduce1 (list1 - list2)---");
    reduce1.parallelStream().forEach(System.out :: println);

    // 差集 (list2 - list1)
    List<String> reduce2 = list2.stream().filter(item -> !list1.contains(item)).collect(Collectors.toList());
    System.out.println("---得到差集 reduce2 (list2 - list1)---");
    reduce2.parallelStream().forEach(System.out :: println);

    // 并集
    List<String> listAll = list1.parallelStream().collect(Collectors.toList());
    List<String> listAll2 = list2.parallelStream().collect(Collectors.toList());
    listAll.addAll(listAll2);
    System.out.println("---得到并集 listAll---");
    listAll.parallelStream().forEach(System.out :: println);

    // to re-union
    List <String> listAllDistinct = listAll.stream () DISTINCT () the collect (Collectors.toList ());.. 
    System.out.println ( "to get a weight --- --- union listAllDistinct"); 
    listAllDistinct.parallelStream () .forEach (System.out :: println); 

    System.out.println ( "--- --- original List1"); 
    . list1.parallelStream () forEach (System.out :: println); 
    System. out.println ( "--- --- original List2"); 
    . list2.parallelStream () forEach (System.out :: println); 

    // generally when the filter operation instead of parallel streams parallelStream, if used, may causes the thread safety problems 
　　// determine the object to be rewritten hash 

}