java - 如何在java中对具有多个数据排序的对象列表进行排序

Question

我在 pojo 类中有很多单值排序示例。

但我想用多个值排序，如下例所示

排序前

Name          City           Roll
--------------------------------------

    sekhar ---------bbsr------------23
    himanshu -------agra------------23
    nitin ----------delhi------------23
    nitin ----------delhi------------22
    nitin ----------bbsr------------23
    arun -----------patna------------23
    arun -----------kendrapara-------23

排序后

Name          City           Roll
--------------------------------------

    arun -------kendrapara------------23
    arun -------patna------------23
    himanshu ----agra------------23
    nitin -------bbsr------------23
    nitin -------delhi------------22
    nitin -------delhi------------23
    sekhar -------bbsr------------23

我的代码在这里

package example;

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

public class Demo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Demo demo = new Demo();
        List<Student> list = new ArrayList<Student>(); // your Car list
        Student st = demo.new Student();
        st.setName("sekhar");
        st.setCity("bbsr");
        st.setRoll(23);
        list.add(st);
        st = demo.new Student();
        st.setName("himanshu");
        st.setCity("agra");
        st.setRoll(23);
        list.add(st);
        st = demo.new Student();
        st.setName("nitin");
        st.setCity("delhi");
        st.setRoll(23);
        list.add(st);
        st = demo.new Student();
        st.setName("nitin");
        st.setCity("delhi");
        st.setRoll(22);
        list.add(st);
        st = demo.new Student();
        st.setName("nitin");
        st.setCity("bbsr");
        st.setRoll(23);
        list.add(st);
        st = demo.new Student();
        st.setName("arun");
        st.setCity("patna");
        st.setRoll(23);
        list.add(st);
        st = demo.new Student();
        st.setName("arun");
        st.setCity("kendrapara");
        st.setRoll(23);
        list.add(st);
        System.out.println("before sort");
        System.out.println("Name:" + "-------------------" + "City...........roll");
        for (Student st1 : list) {
            System.out.println(st1.getName() + " --------------" + st1.getCity() + "------------" + st1.getRoll());
        }

        Collections.sort(list, demo.new CarHorsePowerComparator());
        System.out.println("after sort");
        System.out.println("Name:" + "-------------------" + "City...............roll");
        for (Student st1 : list) {
            System.out.println(st1.getName() + " --------------" + st1.getCity() + "------------" + st1.getRoll());
        }
    }

    public class Student {

        String name;
        String city;
        int roll;

        public int getRoll() {
            return roll;
        }

        public void setRoll(int roll) {
            this.roll = roll;
        }

        public String getCity() {
            return city;
        }

        public void setCity(String city) {
            this.city = city;
        }

        public String getName() {
            return name;
        }

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

    class CarHorsePowerComparator implements Comparator<Student> {
        public int compare(Student stu, Student stu1) {
            int sort = (stu.getName() + stu.getCity() + stu.getRoll()).compareTo((stu1.getName() + stu1.getCity() + stu1.getRoll()));
            return sort;
        }
    }
}

但我正在使用自定义比较器

class CarHorsePowerComparator implements Comparator<Student> {
            public int compare(Student stu, Student stu1) {
                int sort = (stu.getName() + stu.getCity() + stu.getRoll()).compareTo((stu1.getName() + stu1.getCity() + stu1.getRoll()));
                return sort;
            }

它对我有用，但不是正确的方法。如何以正确的方式编写此代码请给我建议。

int sort = (stu.getName() + stu.getCity() + stu.getRoll()).compareTo((stu1.getName() + stu1.getCity() + stu1.getRoll()));

Answer 1

(stu.getName() + stu.getCity() + stu.getRoll()).compareTo((stu1.getName() + stu1.getCity() + stu1.getRoll())) 

表示您正在连接名称、城市和卷号并对结果字符串进行排序。

您应该首先确定排序优先级，然后按该顺序对字段进行排序。查看预期结果似乎您想先按名称排序，然后按城市排序，最后按滚动排序。

class CarHorsePowerComparator implements Comparator<Student> {
            public int compare(Student stu, Student stu1) {
                int sort;
                // Sort on Name first 
                sort = stu.getName().compareTo(stu1.getName);
                if(sort == 0){
                  // If name is equal, sort on city
                  sort = stu.getCity().compareTo(stu1.getCity);
                }   
                if(sort == 0){
                  // If name and city is equal, sort on Roll
                  sort = Integer.compare(stu.getRoll(),stu1.getRoll());
                } 
                return sort;
            }
}