为什么会报错呢？

这是Student类

package com.imooc.collection;

import java.util.HashSet;

import java.util.Set;

public class Student {

public String id;

public String name;

public Set<Course> courses;

public Student(String id, String name) {

// TODO Auto-generated constructor stub

this.id =id;

this.name = name;

this.courses = new HashSet<Course>();

}

}

这是在main 中定义的student对象

Student student = new Student("1","小明");

 为什么会报错呢求大神解答