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

hashcodeidentityjava

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?

Best Solution

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

EDIT: Answer modified following Tom's comment below re. memory addresses and moving objects.