code: public boolean isTypical()
      {
          if (tables.size() == 0) {
              return false;
          }
          for (HuffmanTable table : tables) {
              if (!table.isTypical()) {
                  return false;
              }
          }
          return true;
      }
docs: Evaluates whether all the tables in this {@link HuffmanTablesDirectory}
  are "typical" Huffman tables.
  <p>
  "Typical" has a special meaning in this context as the JPEG standard
  (ISO/IEC 10918 or ITU-T T.81) defines 4 Huffman tables that has been
  developed from the average statistics of a large set of images with 8-bit
  precision. Using these instead of calculating the optimal Huffman tables
  for a given image is faster, and is preferred by many hardware encoders
  and some hardware decoders.
  <p>
  Even though the JPEG standard doesn't define these as "standard tables"
  and requires a decoder to be able to read any valid Huffman tables, some
  are in reality limited decoding images using these "typical" tables.
  Standards like DCF (Design rule for Camera File system) and DLNA (Digital
  Living Network Alliance) actually requires any compliant JPEG to use only
  the "typical" Huffman tables.
  <p>
  This is also related to the term "optimized" JPEG. An "optimized" JPEG is
  a JPEG that doesn't use the "typical" Huffman tables.
  
  @return Whether or not all the tables in this
  {@link HuffmanTablesDirectory} are the predefined "typical"
  Huffman tables.