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

If I have a class, say

class A{
    getA(){

    }
}

class B extend A{
    getB(){

    }
}

Now class B knows two methods getA() and getB(). but class A knows only getA() method.

So, if we have class B obj = new class A(); we have made a mess , as it is valid for class B to reference methods getA() and getB() but only getA() is valid. That explains the issue.

This is my understanding of not allowing child class hold reference of parent class.