我有一个List<UserVO>
每个UserVO都有一个getCountry()
我想根据List<UserVO>
将getCountry()
分组
我可以通过流来完成,但是必须在Java6中完成
这在Java8中。我想要用Java6
Map<String, List<UserVO>> studentsByCountry
= resultList.stream().collect(Collectors.groupingBy(UserVO::getCountry));
for (Map.Entry<String, List<UserVO>> entry: studentsByCountry.entrySet())
System.out.println("Student with country = " + entry.getKey() + " value are " + entry.getValue());
我想要像Map<String, List<UserVO>>
一样输出:
CountryA - UserA, UserB, UserC
CountryB - UserX, UserY
这是使用纯Java的方法。请注意,Java 6不支持Diamond运算符,因此您一直都在明确使用<String, List<UserVO>>
。
Map<String, List<UserVO>> studentsByCountry = new HashMap<String, List<UserVO>>();
for (UserVO student: resultList) {
String country = student.getCountry();
List<UserVO> studentsOfCountry = studentsByCountry.get(country);
if (studentsOfCountry == null) {
studentsOfCountry = new ArrayList<UserVO>();
studentsByCountry.put(country, studentsOfCountry);
}
studentsOfCountry.add(student);
}
流越短,对吗?因此,尝试升级到Java 8!