General methods for optimizing program for speed

Question

What are some generic methods for optimizing a program in Java, in terms of speed. I am using a DOM Parser to parse an XML file and then store certain words in an ArrayList, remove any duplicates then spell check those words by creating Google search URL's for each word, get the html document, locate the corrected word and save it to another ArrayList.

Any help would be appreciated! Thanks.

Answer 1

Why do you need to improve performance? From your explanation, it is pretty obvious that the big bottleneck here (or performance hit) is going to be the IO resulting from the fact that you are accessing a URL.

This will surely dwarf by orders of magnitude any minor improvements you make in data structures or XML frameworks.

It is a good general rule of thumb that your big performance problems will involve IO. Humorously enough, I am at this very moment waiting for a database query to return in a batch process. It has been running for almost an hour. But I welcome any suggested improvements to my XML parsing library nevertheless!

Here are my general methods:

• Does your program perform any obviously expensive task from the perspective of latency (IO)? Do you have enough logging to see that this is where the delay is (if significant)?

• Is your program prone to lock-contention (i.e. can it wait around, doing nothing, waiting for some resource to be "free")? Perhaps you are locking an entire Map whilst you make an expensive calculation for a value to store, blocking other threads from accessing the map

• Is there some obvious algorithm (perhaps for data-matching, or sorting) that might have poor characteristics?

• Run up a profiler (e.g. jvisualvm, which ships with the JDK itself) and look at your code hotspots. Where is the JVM spending its time?