Generics and TreeSets

Question

Working with Generics is definitely my weak spot, and can use some help with this.

The project is to develop a simple order/inventory system that places orders, keeps track of items and inventories, and keeps a record of all inventory and customer addition/removals since the program first started. This requires reading and writing to a file, and I've picked the CSV format to parse. There are two files to parse, one for Customers and one for Items.

I want to use a TreeSet to make additions/searches log N, but am having some trouble with my file parsing. Rather than have two classes with duplicate code working for their object type, I'd like to have a single parse class taking in the set and file path on execution, and processing the file into a complete set of objects, both of whom have differing fields and methods.

The only solution I've come up with is TreeSet<? extends Object>, but that means that I'll have to box, then unbox each object as its accessed in the structure.

Is there an easier way?

Answer 1

Here's an example of what your hierarchy could look like

class CVSParser<T> {
    private final RecordHandler<T> handler;

    public CVSParser<T>(RecordHandler<T> handler) {
       this.handler = handler;
    }

    public Set<T> parse(File f) {
        Set<T> records = new TreeSet<T>();
        for (String line : file ) {  //I'm paraphrasing here
           records.add(handler.parse( splitIntoFields(line) ));
        }
    }
}

interface RecordHandler<T> {
    public T parse(String[] fields);
}

class CustomerHandler implements RecordHandler<Customer> {
   public Customer parse(String[] fields) {
      return new Customer(fields[0], fields[1]);
   }
}

class ItemHandler implements RecordHandler<Item> {
   //...
}

Set<Item> items = new CVSParser<Item>(new ItemHandler()).parse(itemsFile);

Alternatively you could push the generics down to the method level of CVSParser and make it static even:

class CVSParser {
     public static <T> Set<T> parse(RecordHandler<T> handler, File f) {
        //...        
     }
}


Set<Item> items = CVSParser.parse(new ItemHandler(), itemsFile);