code: public Mac createMac() {
          try {
              Mac mac = Mac.getInstance(ALGORITHM);
              mac.init(getKey());
              return mac;
          } catch (GeneralSecurityException e) {
              // Javadoc says HmacSHA256 must be supported by every Java implementation.
              throw new Error(ALGORITHM+" not supported?",e);
          }
      }
docs: Creates a new {@link Mac} object.