Arraylist的sort方法使用，arraylistsort方法

Arraylist的sort方法使用，arraylistsort方法

package com.mac.test;

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

public class ArraylistSort {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<Student>();
        Student s1 = new Student();
        Student s2 = new Student();
        Student s3 = new Student();
        Student s4 = new Student();
        s1.setId(1);
        s1.setName("s1");
        s2.setId(2);
        s2.setName("s2");
        s3.setId(3);
        s3.setName("s3");
        s4.setId(4);
        s4.setName("s4");
        list.add(s2);
        list.add(s1);
        list.add(s4);
        list.add(s3);
        for (Student student : list) {
            System.out.println(student.getId());
        }
        System.out.println("-----------------");
        SortById sb = new SortById();
        Collections.sort(list, sb);
        for (Student student : list) {
            System.out.println(student.getId());
        }
    }
}

class SortById implements Comparator<Object> {
    @Override
    public int compare(Object o1, Object o2) {
        Student s1 = (Student) o1;
        Student s2 = (Student) o2;
        if (s1.getId() < s2.getId()) {
            return 1;
        } else if (s1.getId() == s2.getId()) {
            return 0;
        } 
        return -1;
    }

}
class Student{
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}