In the apidocs I see that an IMendixObject has a method "getState" and the result is something of type "ObjectState" which is an enumeration with values CREATE, NEW, NORMAL. So I think
obj.getState() == ObjectState.NEW
will do the trick.
My best guess would be implementing your own "isNew" in Java.
But I hope there is a prettier easier way :)
public boolean isNew(IMendixObject object) throws CoreException {
Date createdDate = object.getCreatedDate(getContext());
Date changedDate = object.getChangedDate(getContext());
return createdDate != null && changedDate != null && createdDate.equals(changedDate);
}