This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You really should name your classes something other than Parent and Child, if you want to understand inheritance in this regard... but... the reason the first is allowed is because a Child IS-A Parent, but a Parent may not be a Child.
This would make better sense, if you named parent and child to something else... Maybe name the parent class the Dog class. And name the child classes the Beagle class, the Akita class, the Terrier class, etc... The first is allowed because the Akita is a Dog, but a Dog may not be an Akita.
I do understand the base class - child class relation and the idea of inheritance. I am interested in knowing what goes on behind the scenes. The real reason, I mean. Why is it that we can assign the derived class instance to that of a parent class while the other way round is not permitted?
Raj Kamal wrote:
Why is it that we can assign the derived class instance to that of a parent class while the other way round is not permitted?
Another way to think about it is that a Child is a specialized version of a Parent. It can behave like the Parent, and be used everywhere a Parent is used, plus it has extra stuff / features. A Parent cannot be used in place of a Child because it doesn't have the stuff that is specific to a Child.