Java, BigDecimal. Problems with division


I'm trying to calculate a percentage "factor". That is, given a 20%, convert it into 0.2 (my intention is to later multiply values by that and get the 20% of the values).

Anyway, the question is related with this piece of code:

public static void main(String[] args) {
    int roundingMode = BigDecimal.ROUND_FLOOR;
    BigDecimal hundred = new BigDecimal("100");
    BigDecimal percentageFactor = null;
    BigDecimal percentage = new BigDecimal("20");
    BigDecimal value = new BigDecimal("500");
    percentageFactor = percentage.divide(hundred, roundingMode);
    float f = percentage.floatValue() / hundred.floatValue();
    f = value.floatValue() * f;
    BigDecimal aux = value.multiply(percentageFactor);
    System.out.println("final falue:"+aux.toString());
    System.out.println("Float Value:"+f);       

I would expect the outcome of this to be something like:

factor: 0.2
final value: 100
float value: 100

but instead percentage.divide(hundred, roundingMode); is returning zero, an hence I get:

final falue:0
Float Value:100.0

What am I doing wrong? How can I divide two big decimals properly?

By the way, I'm using BigDecimal because I will be calculating monetary percentages, so I want control regarding rounding.

Best Answer

I think that the best solution is to set the requested scale when dividing: In this case perhaps 2.

    var hundred = new BigDecimal(100);
    var percentage = new BigDecimal(20);
    var value = new BigDecimal(500);
    var percentageFactor = 
        percentage.divide(hundred,2, BigDecimal.ROUND_HALF_UP);
    value = value.multiply(percentageFactor);
    System.out.println("final value:"+ value);

Final value: 100.00

The multiplication is using the scale from the factors (0+2) but it can be specified too.

I'd use ROUND_HALF_UP for accounting (in my legislation) or ROUND_EVEN (for statistics) for rounding mode.