CODEWITHSUNDEEP
javafloating-pointdouble
Tobia
Tobia

Reputation: 9524

Java double precision sum trouble

I would like to know why I get this error. (this is Display log of Eclipse debug)

var
     (double) 2.8
tot.getIva()
     (java.lang.Double) 0.17
var+tot.get()
     (double) 2.9699999999999998

I can not understand why I did not get simply 2.97!

Upvotes: 3

Views: 10649

Answers (2)

javatutorial
javatutorial

Reputation: 1944

This is due to the precision of floating point types in java (float and double). If you need indefinite precision you should try using BigDecimal instead of double.

Upvotes: 2

Louis Wasserman
Louis Wasserman

Reputation: 198211

If you wanted 2.97, you should have used BigDecimal.

doubles are stored as fractions in binary, not decimal. So 3.75, for example, is just stored as 2^1 + 2^0 + 2^(-1) + 2^(-2).

2.8 and 0.17 cannot be represented exactly as binary fractions, so there's going to be some rounding error.

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Upvotes: 15

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