I'm currently in the process of learning Java. I have just run the following line in Eclipse in Win7 using jre1.8.0_25:
System.out.println(4.5 * 7.9);
The console output is: 35.550000000000004
I'm just wondering why the output is wrong.
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user207421
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desiguel
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You should read up on int, double and float precision points – Ascalonian Jan 30 '15 at 00:26
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2Welcome to floating point arithmetic! http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html – Chthonic Project Jan 30 '15 at 00:28
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This is normal floating point behavior. If you need precision use BigDecimal. – PM 77-1 Jan 30 '15 at 00:28
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possible duplicate: (floating point numbers) http://stackoverflow.com/q/322749/2777098 – display name Jan 30 '15 at 00:28
3 Answers
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When looking for accuracy, doubles are not the best choice, as they are actually not as perfect as they may seem due to some limitations in their design.
kirbyquerby
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It's not only a Java issue (feature?), it's a common issue for all languages with floating point arithmetics. It's based on IEEE 754 standard, in case you're interested.
kamituel
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It's because of loss of precision due to operations made by the computer in binary. You can see an explanation of it here.
AxiomaticNexus
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1It's also because of imprecision in the input literals. 7.9 cannot be represented accurately in floating-point. – user207421 Jan 30 '15 at 00:40