code: public static final String showControlCharacters(String str) {
  		int len = str.length();
  		StringBuilder sb = new StringBuilder();
  
  		for (int i = 0; i < len; i += 1) {
  			char c = str.charAt(i);
  			switch (c) {
  			case '\b':
  				sb.append("\\b");
  				break;
  			case '\t':
  				sb.append("\\t");
  				break;
  			case '\n':
  				sb.append("\\n");
  				break;
  			case '\f':
  				sb.append("\\f");
  				break;
  			case '\r':
  				sb.append("\\r");
  				break;
  			default:
  				sb.append(c);
  			}
  		}
  
  		return sb.toString();
  	}
docs: Replaces control characters by their escape-coded version. For example,
  if the string contains a line break character ('\n'), this character will
  be replaced by the two characters backslash '\' and 'n'. As a consequence, the
  resulting string will not contain any more control characters.
  
  @param str The string in which to replace the control characters.
  @return The string with the replaced characters.