按属性将对象列表分组：Java

  • Z时代
  • 2024-01-10
  • 分类：问答

我需要使用特定对象的属性（位置）对对象（学生）列表进行分组，代码如下所示，

public class Grouping {
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        List<Student> studlist = new ArrayList<Student>();
        studlist.add(new Student("1726", "John", "New York"));
        studlist.add(new Student("4321", "Max", "California"));
        studlist.add(new Student("2234", "Andrew", "Los Angeles"));
        studlist.add(new Student("5223", "Michael", "New York"));
        studlist.add(new Student("7765", "Sam", "California"));
        studlist.add(new Student("3442", "Mark", "New York"));
        //Code to group students by location
        /*  Output should be Like below
            ID : 1726   Name : John Location : New York
            ID : 5223   Name : Michael  Location : New York
            ID : 4321   Name : Max  Location : California
            ID : 7765   Name : Sam  Location : California    
         */
        for (Student student : studlist) {
            System.out.println("ID : "+student.stud_id+"\t"+"Name : "+student.stud_name+"\t"+"Location : "+student.stud_location);
        }
    }
}
class Student {
    String stud_id;
    String stud_name;
    String stud_location;
    Student(String sid, String sname, String slocation) {
        this.stud_id = sid;
        this.stud_name = sname;
        this.stud_location = slocation;
    }
}

请给我建议一个干净的方法。

回答：

In Java 8:

Map<String, List<Student>> studlistGrouped =
    studlist.stream().collect(Collectors.groupingBy(w -> w.stud_location));

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