Rounding to a fixed relative precision

Question

I get number representing strings like

248.03500000066338
313.44999999979470
4.2346999999

and I need to round them to something like

248.035
313.45
4.2347

while keeping a fixed relative precision of let's say 6 significant figures. I could do it using Math.log10, computing what absolute precision is needed, and rounding correspondingly, but I wonder if there's a simple way.

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Ideally, the resulting number should be such that it does not produce the trailing nines when converted to string, but this is not needed and maybe impossible.

Answer 1

It might not be the most performant solution but I think this is the easiest one:

BigDecimal input = new BigDecimal("248.03500000066338");
double rounded = input.round(new MathContext(6)).doubleValue();