How to use a standard library binary search if I'm not searching for a key?

Question

Hi all,
I'm looking for the tidiest way to code something with maximum use of the standard libraries. I have a sorted set of ints that represent quality levels (let's call the set qualSet ). I want to find the maximum quality level (choosing only from those within qualSet ) for a limited budget. I have a method isAffordable(int) that returns boolean. So one way to find the highest affordable quality is to start at the lowest quality level, iterate through qualSet (it is sorted), and wait until the first time that isAffordable returns false. eg.
int i=-1;
for (int qual : qualSet) {
     if !(isAffordable(qual))
          return i;
     i++;
}However isAffordable is a slightly complicated fn, so I'd like to use a binary search to make the process more efficient. I don't want to write the code for a binary search as that is something that should be reused, ideally from the standard libraries. So my question is what's the best way of reusing standard library code in this situation so as to not write my own binary search?
I have a solution, but I don't find it very elegant. Here are the important classes and objects.
//simple wrapper for an int representing quality level
class QualityElement implements Comparable<QualityElement>
//element to use to search for highest quality
class HiQualFinderEl extends QualityElement {
     HiQualFinderEl(ComponentList cl) {...}
//class that contains fair amount of data and isAffordable method
class ComponentList {
     boolean isAffordable(int qual) {...}
//sorted set of QualityElements
TreeSet<QualityElement> qualSet When you create an instance of HiQualFinderEl, you pass it a reference to a ComponentList (because it has the isAffordable() method). The HiQualFinderEl.compareTo() function returns 1 or -1 depending on whether the QualityElement being compared to is affordable or not. This approach means that the binary search returns an appropriate insertion point within the list (it will never act as if it found the key).
I don't like this because semantically the HiQualFinderEl is not really an element of the list, it's certainly not a QualityElement (but it inherits from it), and it just feels ugly! Any clever suggestions? Btw, I'm new to Java, old to C++.
If this is unclear pls ask,
Andy

Answer 1

Thanks Peter for the reply
Peter__Lawrey wrote:
you are not looking for a standard binary searchI'm not using a binary search in the very common I'm searching for a particular key sense, which is the Collections.binarySearch sense. But binary searches are used in other situations as well. In this case I'm finding a local maximum of a function, I could also be solving f(x)=0... is there a nice generic way to handle other uses of binary search that anyone knows of?
I would just copy the code from Collections.binarySearch and modify itI have this thing about reusing; just can't bring myself to do that :)
It would be quicker and more efficient than trying to shoe horn a solution which expects a trinary result.Not sure I understand the last bit. Are you referring to my bastardised compareTo method with only two results? If so, I know, it is ugly! I don't see how it could be less efficient though???
Thanks,
Andy