code: public static String or(final String first, final String second) {
      final StringBuilder buffer = new StringBuilder();
      for (int i = 0; i < first.length(); i++) {
        if ('0' == first.charAt(i) && '0' == second.charAt(i)) {
          buffer.append('0');
        } else {
          buffer.append('1');
        }
      }
      return buffer.toString();
    }
docs: 比较两个等长字符串的每一位，相或<br>
  适用于仅含有1和0的字符串.
  
  @param first a {@link java.lang.String} object.
  @param second a {@link java.lang.String} object.
  @return a {@link java.lang.String} object.