code: public static final Parser<Boolean> instance() { // NOPMD it's thread save!
      if (BooleanParser.instanceParser == null) {
        synchronized (BooleanParser.class) {
          if (BooleanParser.instanceParser == null) {
            BooleanParser.instanceParser = new BooleanParser();
          }
        }
      }
      return BooleanParser.instanceParser;
    }
docs: returns the instance.
  
  @return Parser