jdk1.7List集合中按照对象中指定字段排序

题目：现在有一个list集合、里面存放着多个Student对象，现要求按照Student的score进行排序

代码演示：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Student {
    public Student(String name, int score) {
        this.name = name;
        this.score = score;
    }

    private String name;
    private int score;

    public String getName() {
        return name;
    }

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

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
    public static void main(String[] args) {
        Student student = new Student("张三",60);
        Student student2 = new Student("李四",30);
        Student student3 = new Student("王五",80);
        Student student4 = new Student("赵六",90);
        List<Student> studentList = new ArrayList<>();
        studentList.add(student);
        studentList.add(student2);
        studentList.add(student3);
        studentList.add(student4);
        System.out.println("排序前");
        for (Student o : studentList) {
            System.out.println(o.getName()+"  "+o.getScore());
        }
        Collections.sort(studentList, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                //排序字段   正序    如果需要倒序则将两个值调换
                return o1.getScore()-o2.getScore();   
            }
        });
        System.out.println("排序后");
        for (Student o : studentList) {
            System.out.println(o.getName()+"  "+o.getScore());
        }

    }
}

结果输出：

jdk1.7List集合中按照map中指定字段排序

题目：现在有一个list集合、里面存放着多个Map，Map中用于存储学生的姓名，语文成绩、数学成绩、英语成绩，现在需要按照语文成绩进行排序输出

代码演示：

import java.util.*;

public class Student {
    public static void main(String[] args) {
       List<Map> studentList = new ArrayList();
    Map map = new HashMap();map.put("姓名","张三");map.put("语文",60);map.put("数学",65);map.put("英语",70);
    studentList.add(map);
        map = new HashMap();map.put("姓名","李四");map.put("语文",80);map.put("数学",40);map.put("英语",50);
        studentList.add(map);
        map = new HashMap();map.put("姓名","王五");map.put("语文",70);map.put("数学",90);map.put("英语",30);
        studentList.add(map);
        System.out.println("排序前");
        for (Map o : studentList) {
            System.out.println(o.get("姓名")+"  "+o.get("语文")+"  "+o.get("数学")+"  "+o.get("英语"));
        }

        Collections.sort(studentList, new Comparator<Map>() {
            @Override
            public int compare(Map o1, Map o2) {
                //排序字段   正序    如果需要倒序则将两个值调换
                return Integer.parseInt(o1.get("语文").toString())-Integer.parseInt(o2.get("语文").toString());
            }
        });
        System.out.println("排序后");
        for (Map o : studentList) {
            System.out.println(o.get("姓名")+"  "+o.get("语文")+"  "+o.get("数学")+"  "+o.get("英语"));
        }
    }
}

结果输出：

 jdk1.8List集合中按照对象中指定字段排序