Strategy Design Pattern, Generics and TypeSafety

Question

I want to create the following Strategy Pattern combined with Factory, but I want it to be typesafe. I have done the following till now:

public interface Parser&         


        

Answer 1

I'd simply pass a Parser to the getResults() method and forget about that factory stuff. Look, if you say:

public  Parser createParser(ParserType typ) { ... }

you are promising that the method will create a parser of any type the caller wants. This is only possible in a type safe way with parsers that all return an empty collection. Moreover, you can't return a Parser from that function, because String is not the same as any type the caller wanted.

If, however, you write:

  public  Collection getResults(String query, Parser parser) {
      ResultSet resultSet = getResultSet(query); //local private method
      Collection results = parser.parse(resultSet);
      return results;
  }

you have exactly what you wanted: the getResult method is independent of how the parser works, and yet it returns a collection of the correct type.

And later, instead of

Collection it = (Collection) getResults("query", APARSER);

you say:

Collection it = getResults("query", new AParser());

This is sound and makes sense.