Do any of your neighbors have avocado trees that bear fruit? If not, you may either be lacking a pollinator for your tree or perhaps you live too close to the ocean. Avocados really dislike salt and if you don't have any nearby neighbors with bearing trees there is probably a reason for that.
As Robguz points out you do need at least 2 trees with different flower types for successful pollination and you also need bees to transfer the pollen. Sharwil has type "B" flowering. You could try planting an "A" like "Greengold" or some other "A" variety. Alternately, you could graft a branch (or more than one of different varieties) onto your tree to provide you with different pollen sources and also to see how different varieties might perform in your particular microclimate.
Those small fruits that drop off early are called avocado "cukes", "fingers" or "cocktail avocados" and they result from inadequate fertilization. I had one pre-existant avocado that produced then when we bought a house about midway up HPP a few years ago then I planted 3 more avocados and now we get a regular crop off that tree.
I found a mention of problems with fruit set specifically on the variety "Sharwil". Here's a link:
http://www.ctahr.hawaii.edu/fb/avocado_cultural.html
UH CTAHR (college of tropical agriculture) actually has tons of info on Avocado growing you can access and download from their website. Like most bureaucracies you may have to poke around some to find what you are looking for but a good starting point might be here:
http://www.ctahr.hawaii.edu/fb/ first go to "fruits" in the upper left hand corner then click on "avocado" again in the upper left hand corner of the page.
The University of Cal also has some good general information but theirs, including recommended varieties is tailored for Cal not Hawaii. Still might be useful though.
http://ucavo.ucr.edu/General/Answers.html