BigDecimal compareTo() problem

[Joe Busch]

I have 3 BigDecimal variables: a, b and c. I then do the following test:
if( a.add(b).compareTo(c) == 0 )

a = 49.9900000000000001827363995
b = 50.01
c = 100

This sum does not equal zero. How do I set the scale/rounding for all three BigDecimals to get the desired result to equal zero? These are dollar and cents amounts.
Thanks,
Joe

[M Beck]

is there any particular reason you have to use BigDecimal in particular to work with these dollar-and-cent amounts? couldn't you just use integers and BigIntegers to work with whole numbers of cents instead? then you wouldn't need to round anything at all.

[Barry Higgins]

Firstly the way I'm running your code actually works fine and returns true

  
            BigDecimal a = new BigDecimal(49.9900000000000001827363995);
            BigDecimal b = new BigDecimal(50.01);
            BigDecimal c = new BigDecimal(100);
            
            System.out.println(a.add(b).compareTo(c)==0);

However if you want it to make it bullet-proof you could try the following

  
            BigDecimal a = new BigDecimal(49.9900000000000001827363995);
            BigDecimal b = new BigDecimal(50.01);
            BigDecimal c = new BigDecimal(100);
            
            a = a.setScale(2, BigDecimal.ROUND_HALF_UP);
            b = b.setScale(2, BigDecimal.ROUND_HALF_UP);
            
            System.out.println(a.add(b).compareTo(c)==0);

Hope this helps,
Barry

[Joe Busch]

Thanks. I should be calling setScale(2, BigDecimal.ROUND_HALF_UP) on each BigDecimal I use, then the compares work properly.

I guess I could have also used a long and moved the dollar amounts, including pennies, into them. However I would then need to convert double to long as well as strings. Since I have only a small number of computations, BigDecimal was the quickest approach.

Thanks again for your solution.