code: @Override
      public void decode(byte[] bytes, StringBuilder buffer) {
          if (bytes == null) {
              // append nothing
              return;
          }
  
          char[] table = CHAR_TABLE;
          for (int i = 0; i < bytes.length; i++) {
              int code = (int)bytes[i] & 0x000000ff;
              if (code == EXTENDED_ESCAPE) {
                  // take next char from extension table
                  table = EXT_CHAR_TABLE;
              } else {
                  buffer.append((code >= table.length) ? '?' : table[code]);
                  // go back to the default table
                  table = CHAR_TABLE;
              }
          }
      }
docs: Decode an SMS default alphabet-encoded octet string into a Java String.