Why doesn't my operation work when I use BigDecimal?

Question

I'm trying to do an operation using BigDecimal but it always return 0. Why does it work when I use double?

public static void main(String[] args) {
    double a = 3376.88;
    BigDecimal b = new BigDecimal(a);
    System.out.println(a-a/1.05);
    System.out.println(b.subtract(b).divide(new BigDecimal(1.05)).doubleValue());
}

Thanks.

Answer 1

You are not performing the same operations.

When you are doing the double operations, the normal java order of operations is applying:

a-a/1.05  
= a - (a/1.05)

But when you are running the methods on BigDecimal, the operations are evaluated in the order you are calling them, so

b.subtract(b).divide(new BigDecimal(1.05))

is equivalent to

(b - b) / 1.05
= 0 / 1.05
= 0