java8List 元素对象单字段去重多字段去重交集差集多字段排序

ゝ一世哀愁。 2023-09-25 23:39 84阅读 0赞

### 1.排序 ###

List list = new ArrayList<>();  
list.add(new User(1, “张三”));  
list.add(new User(4, “赵六”));

list.forEach(f -> f.setUserName("zhao"));
        System.out.println(list);
         list.forEach（f  - > f.setName（f.getName（ ）+"s"））
    
        //条件删除
         list.removeIf(user -> user.getUserId() == 3);
        System.out.println("--------------排序前");
        list.forEach(user -> {
            System.out.println(user);
        });
         list.sort((user1,user2)->user1.getUserId() - user2.getUserId());
        System.out.println("_-------------------正序排序后");
        list.forEach(user -> {
            System.out.println(user);
        });
    
        System.out.println("--------------------倒序排序后：");
         list.sort((((o1, o2) -> o2.getUserId() - o1.getUserId())));
        list.forEach(user -> {
            System.out.println(user);
        });
    	 //多字段排序
        //ArrayList<Student> oldList1 = oldList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(table -> table.getAge() + ";" + table.getNo()))), ArrayList::new));

### 2.list 转成 map ;key:name value:stockCode ###

List list = new ArrayList();  
list.add(new User1(“zhao”, 1, “000002”, “万科A”));  
list.add(new User1(“zhao”, 1, “000002”, “万科A”));  
list.add(new User1(“zhao”, 1, “000002”, “万科A12”));  
//key-value (String-String) key对应字符  
Map<String, String> userMap = list.stream().collect(Collectors.toMap(User1::getName, User1::getStockCode, (k1, k2) -> k2));  
//key-value (String-entity) key对应对象  
Map<String, User1> list2 = list.stream().collect(Collectors.toMap(User1::getName, Function.identity(), (key1, key2) -> key2));  
//key-value (String-entity) 多字段拼接key对应对象  
Map<String, User1> list3 = list.stream().collect(Collectors.toMap(item->item.getName()+item.getAge(),Function.identity(), (key1, key2) -> key2));  
//key-value (String-list) key对应list  
Map<String, List> list4= list.stream().collect(Collectors.groupingBy(t->t.getName()));

### 3. list 去重 ###

List aa = list1.stream().distinct().collect(Collectors.toList());

### 4.list根据对象某一字段值去重 ###

System.out.println(“--------list根据对象某一字段值去重--------”);  
List userList = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User1::getName))), ArrayList::new));

### 5.list多属性去重 辩解 ###

List list1 = list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(u -> u.getName() + “;” + u.getAge()))), ArrayList::new));

### 6.list 取交集 ###

List intersection = list1.stream().filter(item -> list2.contains(item)).collect(Collectors.toList());

### 7.获取元素对象属性值集合 ###

### 8.List 根据Bean的一个属性求两个list的交集 差集 ###

### 9.list 和 List 取差集 ###

Student s1 = new Student(11, “black”, 456);  
Student s2 = new Student(12, “red”, 123);//old  
Student s6 = new Student(13, “red”, 123);//old

Student s3 = new Student(11, "black", 123);
        Student s4 = new Student(12, "red1", 123);
        Student s5 = new Student(15, "white", 123);//new
    
        List<Student> oldList = new ArrayList<Student>() {
       {
            add(s1);
            add(s2);
            add(s6);
        }};
        List<Integer> oldAgeList = oldList.stream().map(x -> x.getAge()).collect(Collectors.toList());
    
        List<Student> newList = new ArrayList<Student>() {
       {
            add(s3);
            add(s4);
            add(s5);
        }};
        //获取元素对象属性值集合
        List<Integer> newAgeList = oldList.stream().map(x -> x.getAge()).collect(Collectors.toList());
    
        //List<Bean> 根据Bean的一个属性求两个list的交集 差集
        //交集
        List<Student> updList = newList.stream()
                .filter(item -> oldList.stream()
                        .map(e -> e.getAge())
                        .collect(Collectors.toList())
                        .contains(item.getAge()))
                .collect(Collectors.toList());
        System.out.println(updList);
    
        // 差集 (new - old)
        List<Student> addList = newList.stream()
                .filter(item -> !oldList.stream()
                        .map(e -> e.getAge())
                        .collect(Collectors.toList())
                        .contains(item.getAge()))
                .collect(Collectors.toList());
        System.out.println(addList);
    
        // 差集 (old - new)
        List<Student> delList = oldList.stream()
                .filter(item -> !newList.stream()
                        .map(e -> e.getAge())
                        .collect(Collectors.toList())
                        .contains(item.getAge()))
                .collect(Collectors.toList());
        System.out.println(delList);
        //list<String> 和 List<Bean> 取差集
        List<String> list3 = new ArrayList<String>() {
       {
            add("aa");
            add("black");
            add("black");
        }};
        List<String> listStr = list3.stream()
                .filter(item -> !newList.stream()
                        .map(e -> e.getHaircolor())
                        .collect(Collectors.toList())
                        .contains(item))
                .collect(Collectors.toList());
        System.out.println(listStr);

### 10.list 获取元素对象单属性值重复的字段数据 返回String ###

List uniqueList = list.stream().collect(Collectors.groupingBy(User1::getStockCode, Collectors.counting()))  
.entrySet().stream().filter(e -> e.getValue() > 1)  
.map(Map.Entry::getKey).collect(Collectors.toList());

### 11.list 获取元素对象多属性值重复的字段数据 返回String ###

List uniqueList2 = list.stream().collect(Collectors.groupingBy(user1 -> user1.getStockCode() + “\#” + user1.getAge() + “\#” + user1.getStockName(), Collectors.counting()))  
.entrySet().stream().filter(e -> e.getValue() > 1)  
.map(Map.Entry::getKey).collect(Collectors.toList());

### 12.list 条件过滤 ###

List<User1> ss = list.stream().filter(user -> (user.getName().equals("zhao") && user.getAge() == Integer.valueOf(1))).collect(Collectors.toList());

### 13.多字段排序 ###

ArrayList oldList1 = oldList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(table -> table.getAge() + “;” + table.getNo()))), ArrayList::new));