假设：
20名老师：T01, T02, ... , T20
8间教室：C01, C02, ... , C08
1.
Teacher.java
int id;
String teacherName;
2.
ClassRoom.java
int id;
String roomName;
3.
TCRelt.java (Teacher_ClassRoom_Relation 的缩写)
int id;
int teacher_id;
int room_id;
然后写 method
public List<ClassRoom> findClassRoomByTeacher(Teacher teacher){};
public List<Teacher> findTeacherByClassRoom(ClassRoom){};
多对多的问题先简化成一对多，然后再求解，比较好思考。
不知道有没有回复到你的问题。