Scala UpperBound和LowerBound概念

class Student {
  def printDetails = println("I am a student")
  def printSomeOtherDetails = println("I love Studying")
}

class ComputerScienceStudent extends Student {
  override def printDetails = println("I am a Computer Science Student")
  override def printSomeOtherDetails = println("I love Scala")
}

class InformationTechnologyStudent extends Student {
  override def printDetails = println("I am an Information Technology Student")
  override def printSomeOtherDetails = println("I love Java")
}

class MyGenericClassForUpperBound {
  def printStudentDetails[S <: Student](student: S) = {
    student.printDetails
    student.printSomeOtherDetails
  }
}

class MyGenericClassforLowerBound {
  def printStudentDetails[S >: ComputerScienceStudent](student: S) = {
    student.printDetails
    student.printSomeOtherDetails
  }
}

MyGenericClassforLowerBound的方法printStudentDetails正在创建问题. student.printDetails和student.printSomeOtherDetails语句告诉我

value printDetails is not a member of type parameter S

据我所知：

> Q [A<：B]表示类/方法Q可以采用A类的任何对象,其中A类是B类的子类型.这称为上限.
> Q [A>：B]表示类/方法Q可以接受类A的任何对象,其中类A是类B的超类型.这称为下限.

如果我的理解是错误的,请帮助我,并帮助我理解为什么上述问题即将到来.多谢你们.