Zayin Krige

How to work with currency in Java by using the BigDecimal type

28 Nov 2009 @ 8:44 AM

As most of you are aware, when working with currency values, FLOAT types just don’t cut it due to their innaccuracy in handling of decimal places. For example – 0.0006 is stored as 0.0005998035. For most instances this is acceptable, BUT when you start working with large values, it becomes a problematic.

Lets say we are writing a banking transaction module that handles 10 million transactions a day. This would result in an inbalance of (10 000 000 x 0.0006) – (10 000 000 x 0.0005998035) = (6000) – (5998.035) = 1.965 out of balance every day. I’m sure you can see why this would become a problem.

The solution? java.math.BigDecimal

However, be warned! BigDecimal isnt a primitive datatype, so you cannot handle it like you would a float.

Lets look at a basic example

^?View Code JAVA

//declare and initialize variables
BigDecimal customer_tx_amount;
BigDecimal customer_tx_vatamount;
BigDecimal vatrate = new BigDecimal("14");
//calculate vatrate divider.
//if vatrate = 14%, then to work out the exclusive amount, we divide the inclusive amount by 
//((100+14)/100), or 1.14
vatrate = vatrate.add(new BigDecimal("100"));
//we want 6 decimal places
vatrate = vatrate.divide(new BigDecimal("100"), 6, BigDecimal.ROUND_HALF_UP);
 
customer_tx_amount = new BigDecimal("235345.37");
customer_tx_vatamount = customer_tx_amount.divide(vatrate, 6, BigDecimal.ROUND_HALF_UP);
customer_tx_vatamount = customer_tx_amount.subtract(customer_tx_vatamount);