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Re: replace extended characters

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On Fri, 11 Feb 2011 18:40:50 -0500, Joshua Cranmer
<Pidgeot18@verizon.invalid> wrote, quoted or indirectly quoted someone
who said :

>The Java compiler will make switch statements into a straight jump table 
>if it's dense enough, but jump tables can wreak havoc on caches and 
>branch predicting, so the JIT may unroll jump tables into better 
>constructs at runtime.

There are two constructs in byte code to support switch:
tableswitch for dense keys which does a jump table and lookupswitch
for sparsekeys which could be implemented with binary search, or
linear search or any of an number of other clever means the JVM could
concoct.

I decompiled a number of switches a while back, and was disappointed
to see it nearly always use lookupswitch, even where I would have used
tableswitch.  This suggests, if you want to guarantee the efficient
version, design your keys to be dense ints starting at 0. You can
often replace a switch with an array or Map data lookup, or array
lookup of a delegate.

Switch is a queer bit of syntax, with its default fallthru. There is
nothing else like it in Java.
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
Refactor early. If you procrastinate, you will have
even more code to adjust based on the faulty design.
.

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Re: replace extended characters Roedy Green <see_website@mindprod.com.invalid> - 2011-02-11 17:05 -0800

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