File APIs for Java Developers
Manipulate DOC, XLS, PPT, PDF and many others from your application.
The moose likes Beginning Java and the fly likes Array Reference assignment Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login

Win a copy of Java Interview Guide this week in the Jobs Discussion forum!
JavaRanch » Java Forums » Java » Beginning Java
Bookmark "Array Reference assignment" Watch "Array Reference assignment" New topic

Array Reference assignment

Anup Om
Ranch Hand

Joined: Dec 30, 2009
Posts: 62
Considering Animal is the superclass of Dog

when I say

An array object is created. Its reference is assigned to a.
This array object can hold three references to Animal.

What is it when I say

Thanks in advance for help.

Maciej Drozdzowski
Ranch Hand

Joined: Dec 30, 2009
Posts: 40

an array object holding three references to Animal - so you can refer to them only by Animal reference, unless you do a cast. inside, it's 3 Dog objects.
a Dog object can also be referenced by an Animal reference, cause Dog-IS-A-Animal
Henry Wong

Joined: Sep 28, 2004
Posts: 20535

Anu Kota wrote:
What is it when I say

In Java, arrays have an hierarchy which mirrors the elements that they contain. Meaning a Dog array IS-A Animal array, since a Dog IS-A Animal. This is why you can assign a Dog array to an Animal array reference.

IMO, you should try to avoid this, because a dog array isn't really an animal array. For example, an animal array can hold cat objects too. If you try to assign a Cat element to the array referred to by reference b, the compiler will allow it, in this case (and yes, it will fail at runtime).


Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor)
I agree. Here's the link:
subject: Array Reference assignment
It's not a secret anymore!