Java8 新特性 list集合利用stream根据对象得某一属性对集合进行分组,附加8之前分组
Java8之后很多新特性，接下来主要讲一下， list集合利用stream根据对象得某一属性对集合进行分组！
话不多说，上代码：
首先准备实体类：
@Data @AllArgsConstructor @NoArgsConstructor public class Student { private Integer id; private String name; //成绩 private Double score; }
然后开始写测试类：
import java.util.*; import java.util.stream.Collectors; public class GroupByName { public static void main(String[] args) { //准备要分组得集合 List<Student> students = Arrays.asList( new Student(1,"伽罗",99d), new Student(2,"后羿",97d), new Student(3,"鲁班",98d), new Student(4,"后羿",90d), new Student(5,"百里",88d), new Student(6,"狼狗",59d), new Student(7,"艾琳",78d), new Student(8,"伽罗",94d) ); //jdk8.0新特性来分组,根据学生姓名来进行分组 Map<String,List<Student>> result = new HashMap<>(); result = students.stream().collect(Collectors.groupingBy(Student::getName)); result.forEach((x,y) -> System.out.println(x+"--"+y)); System.out.println("华丽分割线"+"------------------------"); //jdk1.8之前手写分组 Map<String,List<Student>> map = new HashMap<>(); for (Student student : students) { List<Student> list = map.get(student.getName()); if (list == null) { list = new ArrayList<>(); list.add(student); map.put(student.getName(), list); } else { list.add(student); } } map.forEach((x,y) -> System.out.println(x+"--"+y)); /** * 结果： * 伽罗--[Student(id=1, name=伽罗, score=99.0), Student(id=8, name=伽罗, score=94.0)] * 百里--[Student(id=5, name=百里, score=88.0)] * 狼狗--[Student(id=6, name=狼狗, score=59.0)] * 艾琳--[Student(id=7, name=艾琳, score=78.0)] * 后羿--[Student(id=2, name=后羿, score=97.0), Student(id=4, name=后羿, score=90.0)] * 鲁班--[Student(id=3, name=鲁班, score=98.0)] */ } }
到这里新特性分组就介绍完了，列子简单，直接上手简单，谢谢大家支持！！
