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    <p>Contrary to e.g. C++, the final compilation to native machine code is done at runtime, in this case completely eliminating the need for building two separate versions for performance reasons.</p> <p>If you pass the <code>boolean</code> to enable/disable the extra calls as a parameter to the constructor of the class that implements your algorithm and store it in a <code>final</code> class variable (i.e. a constant), when the algorithm gets executed in a tight loop (= a 'hot spot') the Hotspot VM will compile the class instance and remove the dead code. This kind of runtime optimizations can't be done with C++.</p> <p>But note that a <code>boolean</code> test is likely to cost only a very small fraction of the total algorithm.</p> <p>EDIT: your tests have shown that this doesn't work, although I'm not sure they are done correctly. You are not using any benchmarking framework. The most aggressive optimizations will happen with the server VM (<code>-server</code>) and then code must be properly warmed up first (the first 10000 or so iterations will happen uncompiled which is of course much slower). Also, using a template pattern may have better chance of being optimized than a <code>final boolean</code>, as the boolean check is cheap anyway and the compiler is known to do virtual call inlining (as far as I know).</p> <p>EDIT2: if you don't need to switch at runtime (after all conditional compilation and separate builds won't help you there either) just go with the <code>static final boolean</code> which you know gets optimized. Initialize it with the value from a command line argument or config file and you can easily switch between both versions at application start time.</p>
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    1. POany mechanism in Java to provide compile-time code variants?
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    1. COCould you give us some hard test data that shows that the VM is properly dealing with the dead code in such a situation? A couple of years back tests I saw told that Java was pretty bad at this sort of thing, and I'd like to know if this has changed.
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    2. COOk, this is the magic I was looking for. I am going to try to instantiate one sort object with a final VISUALIZE = true, and another with it false. For static it clearly works, but if it works for objects, this thing is done!
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    3. COAnd... no! It's a great idea, but it doesn't work. The JIT compiler recognizes static final variables, but not final variables that are instantiated at object creation time. The same code turned into an object took 10,000 milliseconds to run. Interestingly, it dropped to 7000 when I commented out the visualization test, so something else is taking longer too. The bottom line though is that Java is definitely not doing as well as a compile-time template mechanism or preprocessor in C++.
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