Android - exact mathematical calculation

Question

I have got a Problem, I am developing an Application which should be able to do some mathematic calculations. These calculations have to be exact (or rather not obviously wrong)

Answer 1

This is a consequence of the IEEE 754 floating point representation, not an error. To deal with it, round your result to an appropriate precision.

Answer 2

Use a BigDecimal for precise floating point calculations. Setting the scale allows you to specify precisely how far out you want to go for output.

import java.math.BigDecimal;

class Test{

        public static void main(String[] args){
                BigDecimal a = new BigDecimal("3.048");
                BigDecimal b = new BigDecimal(1000);
                BigDecimal c = a.divide(b).setScale(6);
                System.out.println(c); //0.003048
        }
}

Answer 3

Use BigDecimal for such precise allocations.

Btw the result for d is obviously right, because double has a machine encoding which cannot store the result, which you perceive as correct.

Answer 4

What you need to use for exact percision is the BigDecimal object:

BigDecimal a = new BigDecimal("3.048");
BigDecimal b = new BigDecimal(1000);

BigDecimal c = a.divide(b);

System.out.println(c); //0.003048