Question

We have to lookup some data based on three input data fields. The lookup has to be fast. There are only about 20 possible lookup combinations. We’ve implemented this using a static HashMap instance where we create a key by concatinating the three data fields. Is there a better way to do this or is this the way to go? Code is below.

Update: I’m not implying that this code is slow. Just curious if there is a better way to do this. I thought there might be a more elegant solution but I’m happy to keep this in place if there are no compelling alternatives!

---

Create class level static HashMap instance:

private static HashMap map = new HashMap();

How we load data into memory:

private void load(Iterator iterator) {        
    while (iterator.next()) {  
      Object o = it.next();
      key = o.getField1() + "-" + o.getField2() + "-" o.getField3();
      map.put(key, o.getData());
    }
}

And how we look up the data based on the three fields:

private Stirng getData(String f1, String f2, String f3) {
   String key = f1 + "-" + f2 + "-" f3;
   return map.get(key);
}

Answer 1

Well, the question to ask yourself is of course “is it fast enough?” Because unless your application needs to be speedier and this is the bottleneck, it really doesn’t matter. What you’ve got is already reasonably efficient.

That being said, if you want to squeeze every bit of speed possible out of this routine (without rewriting it in assembly language 😉 you might consider using an array instead of a HashMap, since there are only a small, limited number of keys. You’d have to develop some sort of hash function that hashes each object to a unique number between 0 and 19 (or however many elements you actually have). You may also be able to optimize the implementation of that hash function, although I couldn’t tell you how exactly to do that without knowing the details of the objects you’re working with.