java 集合分組,集合根據某一條件分組,封裝成map形式
阿新 • • 發佈:2018-12-11
集合中為物件,根據物件中的某一屬性值分組
例子
1、實體類:構造方法、get/set方法、toString方法省略
public class User {
private String id;
private String name;
private String age;
.......
.......
}
2、測試類:
public static void main(String[] args){ List<User> list = new ArrayList<>(); User user1 = new User("1", "張三", "10"); User user2 = new User("2", "張三", "11"); User user3 = new User("2", "張三", "12"); User user4 = new User("4", "李四", "13"); User user5 = new User("5", "李四", "14"); User user6 = new User("6", "李四", "15"); User user7 = new User("7", "王五", "16"); User user8 = new User("8", "王五", "17"); User user9 = new User("9", "王五", "18"); list.add(user1); list.add(user2); list.add(user3); list.add(user4); list.add(user5); list.add(user6); list.add(user7); list.add(user8); list.add(user9); Map<String,List<User>> userGroupMap = list.stream(). collect(Collectors.groupingBy(User::getName)); Set<String> keySet = userGroupMap.keySet(); keySet.forEach((key)->{ System.out.println(key); userGroupMap.get(key).forEach((user)->System.out.println(user)); }); }
結果為:
李四
User [id=4, name=李四, age=13]
User [id=5, name=李四, age=14]
User [id=6, name=李四, age=15]
張三
User [id=1, name=張三, age=10]
User [id=2, name=張三, age=11]
User [id=2, name=張三, age=12]
王五
User [id=7, name=王五, age=16]
User [id=8, name=王五, age=17]
User [id=9, name=王五, age=18]
、
注意:
Map<String,List<User>> userGroupMap = list.stream().
collect(Collectors.groupingBy(User::getName
此句中的User::getName
getName 為物件中某屬性的get方法