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boolean[] vs. BitSet: Which is more efficient?

Asked 2009-03-03T05:40:42.547
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What is more efficient in terms of memory and CPU usage — an array of booleans or a BitSet? Specific BitSet methods are not used, only get/set/clear (==, =, Arrays.fill respectively for an array).

java arrays performance memory bitsets
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From some benchmarks with Sun JDK 1.6 computing primes with a sieve (best of 10 iterations to warm up, give the JIT compiler a chance, and exclude random scheduling delays, Core 2 Duo T5600 1.83GHz):

BitSet is more memory efficient than boolean[] except for very small sizes. Each boolean in the array takes a byte. The numbers from runtime.freeMemory() are a bit muddled for BitSet, but less.

boolean[] is more CPU efficient except for very large sizes, where they are about even. E.g., for size 1 million boolean[] is about four times faster (e.g. 6ms vs 27ms), for ten and a hundred million they are about even.

answered 2009-03-03T07:41:08.687

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