Ordering certain keys in TreeMap / comparator question

Question

I have a TreeMap of currencies. Keys are ("USD", "EUR"...) and each value holds some collection.
I want to sort the TreeMap so that "GBP", "USD", "CAD" and "EUR" are the first 4 keys in the map and other currencies are in their natural order following these 4 keys. I don't know which currency I'll be getting from a certain operation so it could be that "USD" is encountered last which means it will be the last key in my TreeMap.
How would I do this using the Comparator and compareTo method?
Any help would be greatly appreciated.
Cheers
Norm.

Answer 1

Your Comparator's compare() method could have to have a lot of hard-coding in it. Like this:public int compare(Object a, Object b) {
  Thing at = (Thing) a;
  Thing bt = (Thing) b;
  String acurr = a.getCurrency();
  String bcurr = b.getCurrency();
  if (acurr.equals(bcurr)) return 0; // return 0 for equals
  if (acurr.equals("GBP")) return -1; // GBP before everything
  if (bcurr.equals("GBP")) return 1; // GBP before everything
  if (acurr.equals("USD")) return -1; // USD before the rest
  if (bcurr.equals("USD")) return 1; // USD before the rest
  // and so on
}