code: public static String objectId(Object o) {
          if (o == null) {
              return "null";
          } else {
              return o.getClass().getName() + "@" + System.identityHashCode(o);
          }
      }
docs: Returns a string that uniquely identifies the specified object, including
  its class.
  <p>
  The returned string is of form "classname@hashcode", i.e. is the same as the
  return value of the Object.toString() method, but works even when the
  specified object's class has overridden the toString method.
  
  @param o
  may be null.
  @return a string of form classname@hashcode, or "null" if param o is null.
  @since 1.1