java获取两个集合的交集，并集，差集，去重复并集

不念不忘少年蓝@ 2023-10-05 19:08 23阅读 0赞

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

> 1.  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);

> 1.  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);