A)

public static void changePrices(GroceryStore store, BufferedReader input) {
    String itemname = input.readLine();
    double price;
    if (itemname != null) price = Double.parseDouble(input.readLine());
    while (itemname != null) {   
       store.setPrice(itemname, price);
       itemname = input.readLine();
       price = Double.parseDouble(input.readLine());
    }
}

B)

public static String BargainItem(GroceryStore store, String category) {
    String bargain;
    String[] items = store.GetItems(category);
    if (items.length == 0) return "none";
    else {
       bargain = items[0];
       for (int a = 0; a < items.length; a++)
          if (store.getPrice(items[a]) / store.getPrice(items[a]) < store.getPrice(bargain) / store.getSize(bargain))
             bargain = items[a];
       return bargain;
    }
}