Question

I have seen general discussions on OOP and Java with the statement “polymorphism is just a bottom-up method call.” It is not clear to me how is it so. An example would help a lot.

Answer 1

class Top {
   void foo() {...}
}
class Middle extends Top
class Bottom extends Middle

Consider method foo() that is present in Top but can be also in Middle or Bottom. If you have object declared as type Top

Top obj = ...

You can always call method foo() on it. However, obj may be of type Bottom as well, so in polymorphic case you will call foo() on Bottom and if Bottom does not have foo() you call it on Middle and if Middle does not have it, you call it on Top.

So your method call goes from Bottom to Top in a way…