Mathcontext needed for add, subtract and multiply?

Question

first of, my search skills may be not as good as I hoped, so maybe this kind of question exists already. If so please tell me..

See this code below:

new BigDecimal("5").add(new BigDecimal("7"));

vs

new BigDecimal("5").add(new BigDecimal("7"), mathContext);

In which situations would I really need a mathcontext (except divisions)?

I never use a mathcontext unless I divide something. As far as I know this always worked, so what may be the drawbacks here? Do I need a mathcontext on add, subtract and multiply? I'm not so good into the BigDecimal, I simply want to use it to not lose any information like when using doubles. As I sometimes see code with mathcontext on adding something, I'm too afraid to just remove it only because it's my opinion that it is useless...

I read that question but didn't really find a proper answer to my specific question... I begin with BigDecimals without mathcontext and then calculate with them. So my question is, will I ever have drawbacks with this regarding information loss / precision etc? Or will this simply lead to maximum information and that's it?

Edit: I don't want to round, never. In cases of a division like 1/3 I would have to, of course, but in the cases of add, multiply and subtract I don't want any rounding. Do I then need a mathcontext in any circumstance?

score 1 · Accepted Answer · edited May 28 '15 at 08:02

1

If you are doing mathematical operations, that need rounding.

If you add, subtract or multiply two numbers with some decimal parts and you would like to round the result, you also can use mathcontext.

If you don't need to round anything, then you don't need it.

So it is not only limited to avoid problems with endless rest from dividing like 1/3

edited May 28 '15 at 08:02

BAERUS

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answered May 28 '15 at 07:44

Krzysztof Cichocki

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You do not read my post with understanding. – Krzysztof Cichocki May 28 '15 at 07:46
Withdrawn with the edit :-) Didn't see it before posting my answer. – André Stannek May 28 '15 at 07:52
Alright, thanks for answer. So there are no hidden scenarios where an ugly exception can occure for forgetting a math context like it is on divisions? – BAERUS May 28 '15 at 08:02
With just add, subtract and multiply there are no such scenarios :) – Krzysztof Cichocki May 28 '15 at 08:04

score 0 · Answer 2 · answered May 28 '15 at 07:50

I could imagine a case where you want the result to be rounded while de operands are not. An example for addition.

1.23 + 3.01 = 4.24

So, maybe you want your result to have just decimal place, so you would use a MathContext to make it

1.23 + 3.01 = 4.2

I have no idea for a real world example but I think it's immaginable they exist.

Mathcontext needed for add, subtract and multiply?

2 Answers2