code: public boolean truncate(long length)
      throws IOException
    {
      if (length == 0) {
        if (exists()) {
          StreamImpl stream = openWriteImpl();
          stream.close();
  
          clearStatusCache();
  
          return true;
        }
        else
          return false;
      }
      else
        throw new UnsupportedOperationException(getClass().getName() + ": truncate");
    }
docs: Sets the length of the file.
  
  @return true if successful