code: public final IDigest create (final String digestName) {
  
          IDigest digest;
          if (digestName.compareTo("None") == 0) {
              digest = new NullDigest();
          } else if (digestName.compareTo("CRC32C") == 0) {
              digest = new CRC32CDigest();
          } else {
              throw new IllegalArgumentException("Digest Type (" + digestName + ") is unknown.");
          }
  
          return digest;
      }
docs: This method creates an <code>IDigest</code> instance of the given type.
  
  @param digestName The name of the digest type.
  @return The <code>IDigest</code> instance of the given type.