code: public final DataHash getHash() {
          if (outputHash == null) {
              byte[] hash = messageDigest.digest();
              outputHash = new DataHash(algorithm, hash);
          }
          return outputHash;
      }
docs: Gets the final hash value for the digest.
  <p> This will not reset hash calculation.</p>
  
  @return hashValue with computed hash value.
  
  @throws HashException when exception occurs during hash calculation.