I was trying to make my own class for currencies using longs, but apparently I should use BigDecimal
instead. Could someone help me get started? What would be the best way to use BigDecimal
s for dollar currencies, like making it at least but no more than 2 decimal places for the cents, etc. The API for BigDecimal
is huge, and I don't know which methods to use. Also, BigDecimal
has better precision, but isn't that all lost if it passes through a double
? if I do new BigDecimal(24.99)
, how will it be different than using a double
? Or should I use the constructor that uses a String
instead?
Here are a few hints:
BigDecimal
for computations if you need the precision that it offers (Money values often need this).NumberFormat
class for display. This class will take care of localization issues for amounts in different currencies. However, it will take in only primitives; therefore, if you can accept the small change in accuracy due to transformation to a double
, you could use this class.NumberFormat
class, use the scale()
method on the BigDecimal
instance to set the precision and the rounding method.PS: In case you were wondering, BigDecimal
is always better than double
, when you have to represent money values in Java.
PPS:
Creating BigDecimal
instances
This is fairly simple since BigDecimal
provides constructors to take in primitive values, and String
objects. You could use those, preferably the one taking the String
object. For example,
BigDecimal modelVal = new BigDecimal("24.455");
BigDecimal displayVal = modelVal.setScale(2, RoundingMode.HALF_EVEN);
Displaying BigDecimal
instances
You could use the setMinimumFractionDigits
and setMaximumFractionDigits
method calls to restrict the amount of data being displayed.
NumberFormat usdCostFormat = NumberFormat.getCurrencyInstance(Locale.US);
usdCostFormat.setMinimumFractionDigits( 1 );
usdCostFormat.setMaximumFractionDigits( 2 );
System.out.println( usdCostFormat.format(displayVal.doubleValue()) );