java获取两个集合的交集，并集，差集，去重复并集-蒲公英云

java获取两个集合的交集，并集，差集，去重复并集

一.利用java8的新特性
java8 lambda表达式流操作不影响原始list对象;

对象类型处理

List<Student> list1 = new ArrayList<>();
        list1.add(new Student("name100","100"));
        list1.add(new Student("name102","102"));
        list1.add(new Student("name103","103"));
        List<Student> list2 = new ArrayList<>();
        list2.add(new Student("name103","103"));
        list2.add(new Student("name104","104"));
        Set<Student> set1 = new HashSet<>(list1);
        Set<Student> set2 = new HashSet<>(list2);
1）.交集
List<Student> intersection = list1.stream().filter(set2::contains).collect(toList());
        System.out.println("---得到交集 intersection---");
        intersection.parallelStream().forEach(System.out::println);
2）.差集（list1--->list2）
List<Student> reduce1 = list1.stream().filter(item -> !set2.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce1 (list1 - list2)---");
        reduce1.parallelStream().forEach(System.out::println);
3）.差集（list2--->list1）
List<Student> reduce2 = list2.stream().filter(item -> !set1.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce2 (list2 - list1)---");
        reduce2.parallelStream().forEach(System.out::println);
4）.并集
List<Student> listAll = list1.parallelStream().collect(toList());
        List<Student> listAll2 = list2.parallelStream().collect(toList());
        listAll.addAll(listAll2);
        System.out.println("---得到并集 listAll---");
        listAll.parallelStream().forEach(System.out::println);
5）.去重并集
set1.addAll(set2);
        List<Student> listDistinctAll = new ArrayList<>(set1);
        System.out.println("---得到去重并集 listDistinctAll---");
        listDistinctAll.parallelStream().forEach(System.out::println);

简单类型的处理

List<String> list1 = new ArrayList<>();
        list1.add("1");
        list1.add("2");
        list1.add("3");
        List<String> list2 = new ArrayList<>();
        list2.add("3");
        list2.add("4");
        Set<String> set1 = new HashSet<>(list1);
        Set<String> set2 = new HashSet<>(list2);
1）.交集
List<String> intersection = list1.stream().filter(set2::contains).collect(toList());
        System.out.println("---得到交集 intersection---");
        intersection.parallelStream().forEach(System.out::println);
2）.差集(list1 - list2)
List<String> reduce1 = list1.stream().filter(item -> !set2.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce1 (list1 - list2)---");
        reduce1.parallelStream().forEach(System.out::println);
3）.差集(list2 - list1)
List<String> reduce2 = list2.stream().filter(item -> !set1.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce2 (list2 - list1)---");
        reduce2.parallelStream().forEach(System.out::println);
4）.并集
List<String> listAll = list1.parallelStream().collect(toList());
        List<String> listAll2 = list2.parallelStream().collect(toList());
        listAll.addAll(listAll2);
        System.out.println("---得到并集 listAll---");
        listAll.parallelStream().forEach(System.out::println);
5）.去重并集
set1.addAll(set2);
        List<String> listDistinctAll = new ArrayList<>(set1);
        System.out.println("---得到去重并集 listDistinctAll---");
        listDistinctAll.parallelStream().forEach(System.out::println);

二.利用ArrayList自带的方法

List<String> list1 = new ArrayList<String>();
        list1.add("1");
        list1.add("2");
        List<String> list2 = new ArrayList<String>();
        list2.add("2");
        list2.add("3");
1）. 差集（List1中有的但是List2中没有的元素）
list1.removeAll(list2);
        System.out.println(list1);
2）. 并集（不去重）
list1.addAll(list2);
        System.out.println(list1);
3）. 并集（去重）
list1.removeAll(list2);
        list1.addAll(list2);
        System.out.println(list1);
4）. 交集
list1.retainAll(list2);
        System.out.println(list1);