Java学习记录－Lambda表达式示例

//list
List<Integer> userIds=userInfoList.stream().map(m->m.getUserId()).collect(Collectors.toList());
//distinct
List<Integer> userIdsDis=userInfoList.stream().map(m->m.getUserId()).distinct().collect(Collectors.toList());
//array
Integer[] userIdsArray = userInfoList.stream().map(m->m.getUserId()).distinct().collect(Collectors.toList()).toArray(new Integer[0]);
int[] userIdsArray2=userInfoList.stream().mapToInt(m-> Integer.valueOf(m.getUserId())).toArray();
//join
String userIdStr = userInfoList.stream().map(m->m.getUserName()).collect(Collectors.joining(", "));
//filter
List<UserInfo> userInfoList1=userInfoList.stream().filter(m->m.getAge()>10).collect(Collectors.toList());
//get
UserInfo userInfo=userInfoList.stream().filter(m->m.getUserId()==1).findFirst().get();
//new object
List<UserWithCompany> userWithCompanies =userInfoList.stream().map(m->new UserWithCompany(m.getUserId())).collect(Collectors.toList());
//map
Map<Integer,UserInfo> userInfoMap=userInfoList.stream().collect(Collectors.toMap(UserInfo::getUserId, m -> m));
//group
Map<String, List<UserInfo>> singleMap = studentList.stream().collect(Collectors.groupingBy(UserInfo::getCode));
//多条件分组

　Map<String, List<Student>> complexMap = studentList.stream().collect(Collectors.groupingBy(e -> fetchGroupKey(e)));

　　private static String fetchGroupKey(Student student){
　　　　return student.getUsername() +"+"+ student.getCode();
　　}

//for
userInfoList.stream().forEach(m->{ 
　　System.out.println(m.getUserName()); 
　　System.out.println(m.getUserId()); 
});

 

参考资料：

使用java8将list转为map