How to get the unique ID of an object which overrides hashCode()?

Question

When a class in Java doesn't override hashCode(), printing an instance of this class gives a nice unique number.

The Javadoc of Object says about hashCode():

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects.

But when the class overrides hashCode(), how can I get its unique number?

Answer 1

System.identityHashCode(yourObject) will provide the 'original' hash code of yourObject as an integer. Uniqueness isn't fundamentally confirmed. The Sun JVM implementation will give you a value which is similar to the original memory address for this object, but that's an implementation feature and you shouldn't rely on it.

 re. memory addresses and rolling objects.