How to iterate through a treemap in alphabetical order

Question

This is with a servlet. I will have a button for next and previous. When next is pressed, I go to the next record in alphabetical order.
I know how to use a comparator and set it up. I also know how to use an iterator with 'hasNext' function. The problem is that the servlet(or jsp, etc...) will display this to the web. Then a doPost will get called and I have to go to the 'next' or previous record from the last time the form was called.
I don't care about concurrency yet(let me get this part down first). How do i 'track' where I was last and then go to the next record. Or is there an easier way that a treemap. I don't care about performance.

Answer 1

I'm assuming you want to sort on keys, not values, since that's what SortedMaps do.
Let's say you're using elements of class C as the keys in the map. Either have C implement Comparable, or create a Comparator that compares to C instances.
Whether you go the Comparable or Comparator route, the body of the compare or compareTo method will be almost the same. You'll just compare whatever fields are relevant on this/obj (Comparable) or obj1/obj2 (Comparator).
The only other difference is it's more important for Comparable's compareTo to be compatible with equals, which means you have to override equals and hashCode. You don't have to do so for Comparator, but it can make some subtle issues a bit cleaner.
Then you could do something like the following: for (Iterator iter = <something>.iterator(); iter.hasNext();) {
    <SomeClass>sc = iter.next();
    // process this element
} where <something> can be keySet() or entrySet(). Maybe even values(). I think values() will give the sorted order for a SortedMap, but not 100% sure.Check the docs. <SomeClass> will either be the class or the keys (for keySet()), Map.Entry (for entrySet()) or the class of the values (for values()).
You might want to check out this tutorial, if you haven't already.
http://java.sun.com/docs/books/tutorial/collections/