úterý 18. prosince 2012

Java in Eclipse

How to find unused functiones use Core downloads - right click on the class and select "Find Unreferenced Members".

To profile Java applications use JVM Monitor.See http://www.jvmmonitor.org/doc/index.html#Getting_started for instructions.

How to make things fast:
  • Pre-compute rather than re-calculate: any loops or repeated calls that contain calculations that have a relatively limited range of inputs, consider making a lookup (array or dictionary) that contains the result of that calculation for all values in the valid range of inputs. Then use a simple lookup inside the algorithm instead.
    Down-sides: if few of the pre-computed values are actually used this may make matters worse, also the lookup may take significant memory.
  • Don't use library methods: most libraries need to be written to operate correctly under a broad range of scenarios, and perform null checks on parameters, etc. By re-implementing a method you may be able to strip out a lot of logic that does not apply in the exact circumstance you are using it.
    Down-sides: writing additional code means more surface area for bugs.
  • Do use library methods: to contradict myself, language libraries get written by people that are a lot smarter than you or me; odds are they did it better and faster. Do not implement it yourself unless you can actually make it faster (i.e.: always measure!)
  • Cheat: in some cases although an exact calculation may exist for your problem, you may not need 'exact', sometimes an approximation may be 'good enough' and a lot faster in the deal. Ask yourself, does it really matter if the answer is out by 1%? 5%? even 10%?
    Down-sides: Well... the answer won't be exact.

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