java8的lambda过滤list遍历集合，排序

1.根据属性过滤list

List<AllManagerBean> testLists = broadCastRoomMapper.allManagerlist();

List<AllManagerBean> mans = testLists.stream().filter(j->j.getRoomId().equals(roomid)).collect(Collectors.toList());

 //过滤某一属性，成一个新集合

 List<String> uids = testLists.stream().map(e->e.getUserid()).collect(Collectors.toList());

 

2.遍历集合

List<ManagerBean> managerListNew = new ArrayList<ManagerBean>();

if (mans != null ){
mans.forEach(man->{
managerListNew.add(man);
});
}

3.根据某一集合对象中的某一属性，排序

List<Model> thlistbysort = thlist.stream().sorted(Comparator.comparing(Model::getSort)).collect(Collectors.toList());                    //正序

List<Model> thlistbysort = thlist.stream().sorted(Comparator.comparing(Model::getSort).reversed()).collect(Collectors.toList());   //倒序

 

4.对List<String>进行正序，倒序排列

//正序排列

Collections.sort(s);

//倒序排列（先对list正序排列，然后反向排序）

Collections.sort(s);

Collections.reverse(s);//反向排序

5.转成setSet<Integer> ageSet = list.stream().map(Student::getAge).collect(Collectors.toSet()); // [20, 10]

 

6.转成map,注:key不能相同，否则报错
Map<String, Integer> studentMap = list.stream().collect(Collectors.toMap(Student::getName, Student::getAge)); // {cc=10, bb=20, aa=10}

7.字符串分隔符连接
String joinName = list.stream().map(Student::getName).collect(Collectors.joining(",", "(", ")")); // (aa,bb,cc)

8.查询总数
Long count = list.stream().collect(Collectors.counting()); 

9.最大年龄 (最小的minBy同理)
Integer maxAge = list.stream().map(Student::getAge).collect(Collectors.maxBy(Integer::compare)).get(); /

10.所有人的年龄
Integer sumAge = list.stream().collect(Collectors.summingInt(Student::getAge)); 

11.平均年龄
Double averageAge = list.stream().collect(Collectors.averagingDouble(Student::getAge)); 

12.带上以上所有方法
DoubleSummaryStatistics statistics = list.stream().collect(Collectors.summarizingDouble(Student::getAge));
System.out.println("count:" + statistics.getCount() + ",max:" + statistics.getMax() + ",sum:" + statistics.getSum() + ",average:" + statistics.getAverage());

13.分组
Map<Integer, List<Student>> ageMap = list.stream().collect(Collectors.groupingBy(Student::getAge));

14.多重分组,先根据类型分再根据年龄分
Map<Integer, Map<Integer, List<Student>>> typeAgeMap = list.stream().collect(Collectors.groupingBy(Student::getType, Collectors.groupingBy(Student::getAge)));

15.分区
//分成两部分，一部分大于10岁，一部分小于等于10岁
Map<Boolean, List<Student>> partMap = list.stream().collect(Collectors.partitioningBy(v -> v.getAge() > 10));

16.规约
Integer allAge = list.stream().map(Student::getAge).collect(Collectors.reducing(Integer::sum)).get(); //40

 

原创博客，引用请注明出处  https://www.cnblogs.com/guangxiang/p/11077860.html