我试图理解一个开源项目，我在其中遇到了以下类声明:classSTATE_APIAttributeSubject:publicAttributeGroup,publicSubject{public:AttributeSubject(constchar*);virtual~AttributeSubject();virtualvoidSelectAll()=0;virtualconststd::stringTypeName()const;virtualvoidNotify();virtualAttributeSubject*CreateCompatible(conststd::string&