Question

I have a fairly expensive array calculation (SpectralResponse) which I like to keep to a minimum. I figured the best way is to store them and bring it back up when same array is needed again in the future. The decision is made using BasicParameters.

So right now, I use a LinkedList of object for the arrays of SpectralResponse, and another LinkedList for the BasicParameter. And the BasicParameters has a isParamsEqualTo(BasicParameters) method to compare the parameter set.

LinkedList<SpectralResponse> responses LinkedList<BasicParameters> fitParams LinkedList<Integer> responseNumbers 

So to look up, I just go through the list of BasicParameters, check for match, if matched, return the SpectralResponse. If no match, then calculate the SpectralResponse.

Here’s is the for loop I used to lookup.

size: LinkedList size, limited to a reasonable value responseNumber: just another variable to distinguish the SpectralResponse.      for ( i = size-1; i > 0 ; i--) {         if (responseNumbers.get(i) == responseNum)         {             tempFit = fitParams.get(i);             if (tempFit.isParamsEqualTo(fit))             {                 return responses.get(i);             }         }     } 

But somehow, doing it this way no only take out lots of memory, it’s actually slower than just calculating SpectralResponse straight. Much slower.

So it is my implementation that’s wrong, or I was mistaken that precalculating and lookup is faster?

Answer 1

You are accessing a LinkedList by index, this is the worst possible way to access it 😉

You should use ArrayList instead, or use iterators for all your lists.

Possibly you should merge the three objects into one, and keep them in a map with responseNum as key.

Hope this helps!