code: public static boolean isDBCCase(String str)
      {
          if (str != null)
          {
              str += " ";
              for (int i = 0; i < str.length(); i++)
              {
                  String s = str.substring(i, i + 1);
                  int length = 0;
                  try
                  {
                      length = s.getBytes("GBK").length;
                  }
                  catch (UnsupportedEncodingException e)
                  {
                      e.printStackTrace();
                      length = s.getBytes().length;
                  }
                  if (length != 1)
                      return false;
              }
  
              return true;
          }
  
          return false;
      }
docs: 判断该字符串是否是半角字符
  
  @param str
  @return