Question

Is there a good resource to get run times for standard API functions? It’s somewhat confusing when trying to optimize your program. I know Java isn’t made to be particularly speedy but I can’t seem to find much info on this at all.

Example Problem:
If I am looking for a certain token in a file is it faster to scan each line using string.contains(…) or to bring in say 100 or so lines putting them to a local string them performing contains on that chunk.

Answer 1

AFAIK, there are no standard benchmarks for the API methods, and in fact, there could be various implementations based on the JVM you are running. Couple that with the JVM’s JIT optimizations, garbage collections, and a lot of other things, and I doubt you could get globally meaningful numbers. Most you can do is write your own benchmarks.

Some methods specify the computational complexity of the operations in their JavaDocs. Some other methods describe other performance concerns. Make sure you are aware of them and heed them.

But beyond that, most chances are that you are doing premature optimizations. Use a profiler to see it is actually a bottleneck.

For instance, in your case there will be the cost of reading from a file, the cost of placing strings in the large buffer, etc. I’m not sure you can really optimize by reading at the string level. IF this was really mission critical you could read character-by-character and implement a smart matching algorithm without ever creating strings, this might be slightly faster.