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I'm fairly new to Java and I'm writing an android game - and there's one line of code in a tight loop that's really annoying me. 

targetBlocksRemain += letterArray[column][row].isTargetBlock() ? 1 : 0;

I feel like must be possible to write this without the conditional statement and therefore without the potential branch prediction performance hit.

I'll optimise out the tight loop eventually so I'm not massively concerned in the long run, but it'd be nice to know if there's a way to resolve similar situations.

edit Just to clarify - this is a pseudo theoretical questions - there are lots of other things I could do to improve this, such as store isTargetBlock as an int. I'm not really interested in other suggestions, just wondering if there's a way do resolve this particular issue.

edit 2 Hoping to look at what the Dalvik VM is doing shortly to work out how it handles this.

Will Calderwood
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  • Is your application running slow? There is a thing called [premature optimization](http://c2.com/cgi/wiki?PrematureOptimization) – Ceiling Gecko Mar 06 '14 at 09:52
  • @CeilingGecko I'm targeting low end Android devices, and there's no harm in zero cost optimisations as I go along. I didn't come here for a lecture on premature optimisation, I came for an answer. – Will Calderwood Mar 06 '14 at 09:56
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    please have a look at this http://stackoverflow.com/questions/16868196/converting-boolean-to-integer-in-java-without-if-statements - looks like you should not be concerned about branching! – mkorszun Mar 06 '14 at 09:56
  • @mkorszun It would be interesting the see the code produced by the compiler on the Dalvik VM. Anyone got any ideas how I'd go about getting that? – Will Calderwood Mar 06 '14 at 10:00
  • If you want to see the Dalvik VM code, then you'd need to compile your app, then decompile it into Dalvik Bytecode (or something along those lines) - there's free software that does this for you – Ben Ezard Mar 06 '14 at 11:28
  • @BenEzard Really it's the code produced by the JIT that I want to look at. I've found several tools for reverse engineering an APK, but that's not really what I'm interested in - although I suppose it's a good place to start. Hopefully I'll have time to take a look at this a little later. – Will Calderwood Mar 06 '14 at 11:42
  • No idea how good the Dalvik JIT/their new AOT compiler is, but HotSpot or any other "desktop" JVM would optimize this to a cmov (for ARMv6 code I guess it'd be two masked moves? Aarch64 has a cmov instruction again). No idea how to check the JITed code on Dalvik though. – Voo Mar 07 '14 at 13:42

1 Answers1

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I know it might not look good but will avoid conditional statement:

do this once in the activity:

HashMap<Boolean, Integer> map=new HashMap<Boolean, Integer>();
map.put(false, 0);
map.put(true, 1);

and in loop

targetBlocksRemain += map.get(letterArray[column][row].isTargetBlock());
vipul mittal
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  • This won't help. It does not avoid a conditional statement at all. To get something out of a `HashMap`, the key's `hashCode` method gets called. The `hashCode` method for a `Boolean` includes the ternary operator. So this gives you a ternary operator, plus a whole lot of extra stack-juggling stuff associated with the method calls. This is the opposite of an optimisation. – Dawood ibn Kareem Mar 06 '14 at 10:00