问题描述：

我运行编程练习,报错如下,请问哪里有问题?

相关代码：

//实现Comparator接口
public class StudentTest implements Comparator<Student>{

    //实现接口中的方法
    public int compare(Student s1, Student s2){
        String name1 = s1.getName();
        String name2 = s2.getName();
        return name1.compareTo(name2);
    }
    public static void main(String[] args){
        //定义Student类的对象
        Student s1 = new Student(40,20,"peter");
        Student s2 = new Student(28,5,"angel");
        Student s3 = new Student(35,18,"tom");

        //将对象添加到List中
        List<Student> list = new ArrayList<Student>();
        list.add(s1);
        list.add(s2);
        list.add(s3);

        //输出排序前的数据
        System.out.println("按名字排序前:");
        for(Student s:list){
            System.out.println(s);
        }

        //排序
        Collections.sort(list, new StudentTest());

        //输出排序后的数据
        System.out.println("按名字排序后:");
        for(Student s:list){
            System.out.println(s);
        }
    }
}

public class Student {
    //成员变量
    private int num;
    private int age;
    private String name;

    //构造方法
    public Student(){};
    public Student(int num, int age, String name){
        this.setNum(num);
        this.setAge(age);
        this.setName(name);
    }

    //getter和setter方法
    public void setNum(int num){
        this.num = num;
    }
    public int getNum(){
        return this.num;
    }
        public void setAge(int age){
        this.age = age;
    }
    public int getAge(){
        return this.age;
    }
        public void setName(String name){
        this.name = name;
    }
    public String getName(){
        return this.name;
    }
    //toString()方法
    public String toString(){
        return "[学号:"+this.getNum()+", 年龄:"+this.getAge()+", 姓名:"+this.getName()+"]";
    }
}

相关截图：