Interpreter pattern : Example

Given any string expression and a token, filter out the information you want.

The below is a simple parser program.

• The myParser method can be used to parse any expression.
• The composite, visit and iterator patterns have been used.

class Parser{

    private String expression;

    private String token;

    private List result;

    private String interpreted;

    

    public Parser(String e, String t) {

       expression = e;

       token = t;

    }

    

    public void myParser() {  

        StringTokenizer holder = 

                   new StringTokenizer(expression, token);

        String[] toBeMatched = new String[holder.countTokens()];  

        int idx = 0;

        while(holder.hasMoreTokens()) {

            String item = holder.nextToken();

            int start = item.indexOf(",");

            if(start==0) {

               item = item.substring(2);

            }   

        toBeMatched[idx] = item;

        idx ++;

        }

        result = Arrays.asList(toBeMatched);

     }

     public List getParseResult() {

        return result;

     }

     public void interpret() {

         StringBuffer buffer = new StringBuffer();

         ListIterator list = result.listIterator();

         while (list.hasNext()){

            String token = (String)list.next();

            if (token.equals("SFO")){

               token = "San Francisco";          

            }else if(token.equals("CA")) {

               token = "Canada";

            }

            //...

            buffer.append(" " + token);

         }

         interpreted = buffer.toString();        

     }

     public String getInterpretedResult() {

        return interpreted;

     }

     public static void main(String[] args) {

         String source = "dest='SFO',origin='CA',day='MON'";

         String delimiter = "=,'";

         Parser parser = new Parser(source, delimiter);

         parser.myParser();

         parser.interpret();

         String result = parser.getInterpretedResult();

         System.out.println(result);

     }

}