code: public void setIllegalCharacters(final String illegalCharacters) {
          // Create a simple sub-rule taking care of the check
          this.illegalCharacters = illegalCharacters;
          delegatePattern = new NegateBooleanRule<String>(new StringRegexRule("[" + Pattern.quote(illegalCharacters) +
                  "]"));
  
          // Create a nicely space-separated list of illegal characters
          final int illegalCharacterCount = illegalCharacters.length();
          final StringBuilder illegalCharactersSeparatedBySpacesStringBuilder = new StringBuilder(illegalCharacterCount
                  * 2);
          for (int i = 0; i < illegalCharacterCount; i++) {
              illegalCharactersSeparatedBySpacesStringBuilder.append(illegalCharacters.toCharArray()[i]);
              if (i < (illegalCharacterCount - 1)) {
                  illegalCharactersSeparatedBySpacesStringBuilder.append(' ');
              }
          }
          illegalCharactersSeparatedBySpaces = illegalCharactersSeparatedBySpacesStringBuilder.toString();
      }
docs: Sets the list of illegal characters in a string.
  
  @param illegalCharacters String containing all illegal characters.