谢谢解答，本人太粗心了

package com.imooc.collection;
import java.util.HashSet;
public class Student {
    public String id;
    public String name;
    public Set<Course> courses;
    public Student (String id,String name) {
        this.id = id;
        this.name = name;
        this.courses = new HashSet<Course>();
    }

Student类写对了吗？是不是写成下面这样了

public Set<Course> Courses;