How much memory does a Java object use when all its members are null?

Question

Is it correct to assume a Java object only takes up the 8 bytes for the object reference as long as all it's members are set to null or does the definition of members already use up space in the instance for some reason?

In other words, if I have a large collection of objects that I want to be space efficient, can I count on leaving unused members set to null for reducing memory footprint?

Answer 1

No, you need either 4 or 8 bytes ( depending whether it's a 32 or 64 bit system ) for each null you are storing in a field. How would the object know its field was null if there wasn't something stored somewhere to tell it so?

Answer 2

No, null is also information and has also to be stored.