重写Compare方法对集合以指定对象的属性进行排序

import java.io.Serializable;

public class Student implements Serializable {
private static final long serialVersionUID = 8553487662223781924L;
private Integer id;
private String name;
private String birthday;

public Student() {
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getBirthday() {
return birthday;
}

public void setBirthday(String birthday) {
this.birthday = birthday;
}

@Override
public String toString() {
return "Student{" + "id=" + id + ", name='" + name + ", birthday=" + birthday + "}";
}
}

import com.ucarinc.bean.Student;

import java.util.Comparator;

public class SortStudentsById implements Comparator {
@Override
public int compare(Object o1, Object o2) {
Student stu1 = (Student)o1;
Student stu2 = (Student)o2;
// ID从小到大排列
return stu1.getId().compareTo(stu2.getId());
// ID从大到小排列
// return stu2.getId().compareTo(stu1.getId());
}
}

import com.ucarinc.bean.Student;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Comparator;
import java.util.Date;

/**
* 按照生日对学生进行排序
*/
public class SortStudentsByBirthday implements Comparator {
@Override
public int compare(Object o1, Object o2) {
Student stu1 = (Student) o1;
Student stu2 = (Student) o2;
DateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
try {
Date birthday1 = sdf.parse(stu1.getBirthday());
Date birthday2 = sdf.parse(stu2.getBirthday());
// 按照生日从早到晚排序
return birthday1.compareTo(birthday2);
// 按照生日从晚到早排序
// return birthday2.compareTo(birthday1);
} catch (ParseException e) {
e.printStackTrace();
}
return 0;
}
}

public static void main(String[] args) {
// 得到学生的集合
List<Student> studentList = getStudentList();
printStudentList("排序前", studentList);
System.out.println("------------------------------------");
// 根据ID进行排序
Collections.sort(studentList, new SortStudentsById());
printStudentList("根据ID排序后", studentList);
System.out.println("------------------------------------");
// 根据生日进行排序
Collections.sort(studentList, new SortStudentsByBirthday());
printStudentList("根据ID排序后,再根据生日排序", studentList);
}

private static List<Student> getStudentList() {
List<Student> students = new ArrayList<>();

Student stu1 = new Student();
stu1.setId(3);
stu1.setBirthday("1973-01-01 00:00:00");
stu1.setName("刘能");

Student stu2 = new Student();
stu2.setId(1);
stu2.setBirthday("1973-01-01 12:00:00");
stu2.setName("赵四");

Student stu3 = new Student();
stu3.setId(2);
stu3.setBirthday("1999-09-09 09:09:19");
stu3.setName("谢广坤");

students.add(stu1);
students.add(stu2);
students.add(stu3);
return stu
4000
dents;
}

private static void printStudentList(String type, List<Student> students) {
for (Student student : students) {
System.out.println(type + student);
}
}

排序前Student{id=3, name='刘能, birthday=1973-01-01 00:00:00}
排序前Student{id=1, name='赵四, birthday=1973-01-01 12:00:00}
排序前Student{id=2, name='谢广坤, birthday=1999-09-09 09:09:19}
------------------------------------
根据ID排序后Student{id=1, name='赵四, birthday=1973-01-01 12:00:00}
根据ID排序后Student{id=2, name='谢广坤, birthday=1999-09-09 09:09:19}
根据ID排序后Student{id=3, name='刘能, birthday=1973-01-01 00:00:00}
------------------------------------
根据ID排序后,再根据生日排序Student{id=3, name='刘能, birthday=1973-01-01 00:00:00}
根据ID排序后,再根据生日排序Student{id=1, name='赵四, birthday=1973-01-01 12:00:00}
根据ID排序后,再根据生日排序Student{id=2, name='谢广坤, birthday=1999-09-09 09:09:19}