Android :: HashMap / ArrayList And Fastest Way To Iterate Collections On Android

Simple question, what is the fastest way to iterate through collections on Android? I generally use collection.iterator(); and the iterator.next() to iterate through the whole collection. Is it any faster to drop that and iterate with "old" (and I use the term old loosely) for( int i=0; i<collection.size(); i++) ? I was thinking of getting the collection.size() into a separate variable so I wouldn't be asking the collection it's size all the time so basically the for loop would turn into something like this: int size = collection.size(); for( int i=0; i<size; i++ ) collection.get(i); Any better? Speed wise, I mean. I'm in a point where I need to get every possible inch of speed for my application. Or maybe allocate everything into Lists in the start, and once I know the correct amount of data, I turn all that into arrays and drop the Lists so I can have array[index] (Log(1) access, right? OH wait. how did this go again access instead of having the "slow" method calls in between like .get(); when accessing the data in the collection.

And what about getters & setters for Classes? Like let's have a Vector2D class that contains obvious integer x and integer y values. What is the fastest way to access them inside the class? Have them as public and just straight Vector2D.x = someValue; or through getters and setters? I've had much debate with my tutor about this (working on my final year project) but not to get too much into details of it. Also all links for further Android application optimisation are more than welcome and greatly appreciated (I read the googles docs on this already). Plus if you have found some really good tricks / quirks on Android to punish the device even more so it runs faster, do share, do share. Please be gentle on me, I'm such a beginner in all things Android that I feel absolutely dumb as a boot for asking these kind of things. I come from strong C++ / Java background but getting the extra inch of speed for everything on Android is so different than optimizing code for PC side and not that you even have to do it on PC side that often.