怎么给list内的对象排序？

首先，对象要实现Comparable接口，自然需要重写compareTo方法

在compareTo里定义哪个排前面,中间就是return 0

compareTo方法中要确定：

1.拿哪个属性比较

2.怎么样就可以排在前面

3.排在前面返回1，排在后面返回-1

public class Employee implements Comparable<Employee>{
    private int id;
    private String name;
    private int age;
    public Employee(int id,String name,int age){
        this.id = id;
        this.name = name;
        this.age = age;
    }
    @Override
    public int compareTo(Employee o) {

        if(id > o.getId()){
            return 1;
        }else if(id < o.getId()){
            return -1;
        }

        return 0;
    }
    /**
     * @return the id
     */
    public int getId() {
        return id;
    }
    /**
     * @param id the id to set
     */
    public void setId(int id) {
        this.id = id;
    }
    /**
     * @return the name
     */
    public String getName() {
        return name;
    }
    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
    /**
     * @return the age
     */
    public int getAge() {
        return age;
    }
    /**
     * @param age the age to set
     */
    public void setAge(int age) {
        this.age = age;
    }
    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("员工编号:"+getId()+",");
        sb.append("员工姓名:"+getName()+",");
        sb.append("员工年龄:"+getAge());
        return sb.toString();
    }
    

list内对象的排序：

1.声明list

2.添加元素

3.用Collections.sort(list);方法完成排序

public static void main(String[] args) {

        List<Employee> list = new ArrayList<Employee>();
        list.add(new Employee(3,"王志",21));
        list.add(new Employee(2,"李农",22));
        list.add(new Employee(1,"郭楠",23));
        //先遍历，在遍历中打印每个对象
        System.out.println("排序前:");
        for(Employee e : list){
            System.out.println(e);
        }
        Collections.sort(list);
        System.out.println("排序后:");
        for(Employee e : list){
            System.out.println(e);
        }

    }