用hibernate注解写了一个多对多的案例，为何中间表数据只插入了一部分？

Question

@Test
 public void test2(){
     Session session = HibernateUtils.getSession();
     Transaction tx = session.beginTransaction();
     Teacher t1=new Teacher("T001","张老师");
     Teacher t2=new Teacher("T002","李老师");
     Teacher t3=new Teacher("T003","王老师");
     Teacher t4=new Teacher("T004","胡老师");
     //创建学生类
     Student stu1=new Student(2,"男","java",new Date(),"lg");
     Student stu2=new Student(1,"女","java",new Date(),"lr");
     Student stu3=new Student(3,"男","java",new Date(),"zs");
     Student stu4=new Student(4,"女","java",new Date(),"lh");
     //创建教师集合
     Set<Teacher> s1=new HashSet<Teacher>();
     s1.add(t1);
     s1.add(t2);
     s1.add(t3);
    
     Set<Teacher> s2=new HashSet<Teacher>();
     s1.add(t1);
     s1.add(t4);
     s1.add(t3);
    
     Set<Teacher> s3=new HashSet<Teacher>();
     s1.add(t1);
     s1.add(t2);
     s1.add(t4);
    
     Set<Teacher> s4=new HashSet<Teacher>();
     s1.add(t3);
     s1.add(t2);
     s1.add(t4);
    
     stu1.setTeachers(s1);
     stu2.setTeachers(s2);
     stu3.setTeachers(s3);
     stu4.setTeachers(s4);
     session.save(t1);
     session.save(t2);
     session.save(t3);
     session.save(t4);
    
     session.save(stu1);
     session.save(stu2);
     session.save(stu3);
     session.save(stu4);
     tx.commit();
     session.close();
 }

Answer 1

  Set<Teacher> s1=new HashSet<Teacher>();      s1.add(t1);//这边是S1      s1.add(t2);//这边是S1      s1.add(t3);//这边是S1            Set<Teacher> s2=new HashSet<Teacher>();      s1.add(t1);//这边是S1,这边不应该是s2.add(t1)?依次类推      s1.add(t4);//这边是S1      s1.add(t3);//这边是S1            Set<Teacher> s3=new HashSet<Teacher>();      s1.add(t1);//这边是S1      s1.add(t2);//这边是S1      s1.add(t4);//这边是S1            Set<Teacher> s4=new HashSet<Teacher>();      s1.add(t3);//这边是S1      s1.add(t2);//这边是S1      s1.add(t4);//这边是S1