Subtract and round double values by multiplier

Question

I have two double values

double a = 1.07522;
double b = 1.0752;

and rounding multiplier value

public static final double ROUND_MULTIPLIER = 100000.0;

So there always should be 5 decimal places.

I need to subtract two double values and get result as a - b = 0.00002.

How can I do this with using ROUND_MULTIPLIER ?

I tried using BigDecimal as

BigDecimal.valueOf(a).subtract(BigDecimal.valueOf(b)).round(new MathContext((int)ROUND_MULTIPLIER)); 

but it not always works, sometimes return 2E-16, it returns weird value when try add to second value as below

BigDecimal.valueOf(a).subtract(BigDecimal.valueOf(b + 0.00002)).round(new MathContext((int)ROUND_MULTIPLIER));

I need to use ROUND_MULTIPLIER.

Answer 1

I don't understand why you must use ROUND_MULTIPLYER and what the exact reason of it's existance is, so I can only guess.

Forcing the code to use ROUND_MULTIPLYER:

public static final double ROUND_MULTIPLIER = 100000.0;

public void foobar()
{
    double a = 1.07522;
    double b = 1.0752;

    BigDecimal opA = BigDecimal.valueOf(a);
    BigDecimal opB = BigDecimal.valueOf(b);

    BigDecimal result = opA.subtract(opB);

    result = result.multiply(BigDecimal.valueOf(ROUND_MULTIPLIER));

    int cutResult = result.intValue();

    result = BigDecimal.valueOf(cutResult / ROUND_MULTIPLIER);

    System.out.println(result);
}

The output of this is

 0.000020

Is that what you want? The code is definitly object to optimization, but I let that up to you to do ;-)