Why can't reference to child Class object refer to the parent Class object?

Question

I was explaining OOP to my friend. I was unable to answer this question. (How shameful of me? :( )

I just escaped by saying, since OOP depicts the real world. In rea

Answer 1

class "Child" extends "Parent"

"child class object is inherently a parent class object"

 Child aChild = new Child();
 Parent aParent = new Parent();
 aParent = aChild;// is perfectly valid.
 aChild = aParent;// is not valid.

in a code segment like a normal assignment operation, the above is read from right to left. line 3 of the code segment reads - "aChild (a Child class object) is a Parent" (due to inheritence child class objects become superclass objects inherently) thus line no.3 is valid.

whereas in line no.4 it reads, "aParent (a Parent class object) is a child" (inheritence doesn't say that superclass objects will become child class objects. it says the opposite) thus line no.4 is invalid.