Other methods, which are necessary for the account all of the semiconductor lasers characteristics, are possible to make pure virtual. In this case class C Laser is abstract, that is, it's impossible directly to create the object of a C Laser class. It was possible to create the object, it is necessary in heir-classes to realize virtual methods. And it is valid from the physical point of view there cannot be simply a laser, it should be concrete, for example multi-mode (BH, CSP) or single-mode (DBR, DFB).