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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You should read up on int, double and float precision pointsAscalonian– Ascalonian2015-01-30 00:26:58 +00:00Commented Jan 30, 2015 at 0:26
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2Welcome to floating point arithmetic! docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.htmlChthonic Project– Chthonic Project2015-01-30 00:28:10 +00:00Commented Jan 30, 2015 at 0:28
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This is normal floating point behavior. If you need precision use BigDecimal.PM 77-1– PM 77-12015-01-30 00:28:30 +00:00Commented Jan 30, 2015 at 0:28
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possible duplicate: (floating point numbers) stackoverflow.com/q/322749/2777098display name– display name2015-01-30 00:28:42 +00:00Commented Jan 30, 2015 at 0:28
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3 Answers
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.
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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.
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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.
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user207421
It's also because of imprecision in the input literals. 7.9 cannot be represented accurately in floating-point.