拉姆达表达式实现对集合中的对象中的某个属性求和以及查询某个特定属性以及对特定属性求和以及针对集合根据某个属性以key-value形式分组

本文主要是介绍拉姆达表达式实现对集合中的对象中的某个属性求和以及查询某个特定属性以及对特定属性求和以及针对集合根据某个属性以key-value形式分组，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

废话不多说直接上代码求和

List<UserEntity> userEntities = new ArrayList<UserEntity>();userEntities.add(new UserEntity(20L, "张三",1,1L));userEntities.add(new UserEntity(20L, "张三",1,1L));userEntities.add(new UserEntity(22L, "李四",2,2L));userEntities.add(new UserEntity(10L, "王五",3,3L));//        Map<String, List<UserEntity>> user = userEntities.stream().collect
//                (Collectors.groupingBy(UserEntity::getAge));Long collect1 = userEntities.stream().collect(Collectors.summingLong(UserEntity::getAge));Long collect2 = userEntities.stream().collect(Collectors.summingLong(UserEntity::getSex));Long collect3 = userEntities.stream().collect(Collectors.summingLong(UserEntity::getUserId));System.out.println(collect1+"000");System.out.println(collect2+"+++");System.out.println(collect3+"---");

运行结果

7000
7+++
72---

代码查询特定属性

 List<UserEntity> userEntities = new ArrayList<UserEntity>();userEntities.add(new UserEntity(20L, "张三",1,1L));userEntities.add(new UserEntity(20L, "张三",1,1L));userEntities.add(new UserEntity(22L, "李四",2,2L));userEntities.add(new UserEntity(10L, "王五",3,3L));//        Map<String, List<UserEntity>> user = userEntities.stream().collect
//                (Collectors.groupingBy(UserEntity::getAge));List<Long> collect1 = userEntities.stream().map(UserEntity::getAge).collect(Collectors.toList());List<Long> collect2 = userEntities.stream().map(UserEntity::getUserId).collect(Collectors.toList());List<Integer> collect3 = userEntities.stream().map(UserEntity::getSex).collect(Collectors.toList());System.out.println(collect1+" ===");System.out.println(collect2+" ---");System.out.println(collect3+" 000");double sum = userEntities.stream().mapToDouble(UserEntity::getUserId).sum();System.out.println(sum+" sum");

运行结果

[1, 1, 2, 3] ===
[20, 20, 22, 10] ---
[1, 1, 2, 3] 000
72.0 sum

代码分组

List<UserEntity> userEntities = new ArrayList<UserEntity>();userEntities.add(new UserEntity(20L, "张三",1,1L));userEntities.add(new UserEntity(20L, "张三",1,1L));userEntities.add(new UserEntity(22L, "李四",2,2L));userEntities.add(new UserEntity(10L, "王五",3,3L));//        Map<String, List<UserEntity>> user = userEntities.stream().collect
//                (Collectors.groupingBy(UserEntity::getAge));Map<Long, List<UserEntity>> collect = userEntities.stream().collect(Collectors.groupingBy(UserEntity::getAge));System.out.println(collect+" collect");

结果

{1=[UserEntity{userId=20, username='张三', sex=1, age=1}, UserEntity{userId=20, username='张三', sex=1, age=1}],
2=[UserEntity{userId=22, username='李四', sex=2, age=2}],
3=[UserEntity{userId=10, username='王五', sex=3, age=3}]} collect