Why cast after an instanceOf?

Question

In the example below (from my coursepack), we want to give to the Square instance c1 the reference of some other object p1, but only i

Answer 1

E.g. If you hand over p1 as of type Object, the compiler wouldn't know that it is in fact an instance of Square, so that Methods etc. wouldn't be accessible. The if simply checks for a certain type to return true/false, but that doesn't change the type of the variable p1.