How to collapse the inheritance hierarchy into a linear chain?

Question

OOP

In Robert Martin's book, How to Become a Software Development Professional, there is a phrase "They turn the switch into a polymorphic construct or collapse the inheritance hierarchy into a linear chain."
Please clarify the second.

Answer 1

They'll transform a switch statement into polymorphic deployment, or collapse an
inheritance hierarchy into a chain-of-command . In short, they treat software
the way a sculptor treats clay—they continuously shape and mold it.
inheritance hierarchy into a linear order of subordination
(see comment for an example)