@Entity
class Student{
long 
@ManyToMany
Set<Course> courses;
}

@Entity
class Course{
@ManyToMany
Set<Student> students;
}

  Course couse1=new Course();
  Course couse2=new Course();
  Student student1=new Student();
  Student student2=new Student();
 student1.setCourses(Arrays.asList(couse1,couse2));
 student2.setCourses(Arrays.asList(couse1,couse2));