Custom class for monetary amount (money value) instead of BigDecimal

Question

On StackOverflow I found multiple advices to stick with BigDecimal in Java instead of reinventing the wheel.

Despite that, I decided to create my custom class, and I would ask if that was a good idea and pros or cons about my design in comparsion to BigDecimal. The reasons to choose custom implementation and characteristic of my design are:

• no double/float constructors like in BigDecimal (risk of mistake) - long internally with 8 decimal places - this restrics min/max to ~10 bilion but system is cryptocurrency-targeted so typical values are small.
• no difference in "0.0" and "0.00" as BigDecimal have
• simple SQL compatibility by BIGINT column
• hard connection to currency object/code - cannot create amount wihtout currency and also cannot do arthimethic/comparsion of two values in different currencies
• Control of creation possible values to not overflow long (-10 bilion to 10 bilion)
• internal overflow protection on computations

Do you think that those reasons as good to choose custem implementation instead of BigDecimal?

To minimize risks I have cover very lot of situations by unit test and also use BigDecimal for initial conversion from string:

BigDecimal decimal = new BigDecimal(value);
... check MIN/MAX allowed values ...
BigDecimal multiplied = decimal.multiply(new BigDecimal(String.valueOf(DECIMAL_DIVIDER)));
long internalResult = multiplied.toBigInteger().longValue();
return new Amount(internalResult, cryptoCurrency.getInternalCode());

Answer 1

Your reasons for creating a custom class are perfectly valid. If your system was only working with a single currency, the argument for creating a custom class would be much weaker. But with multiple currencies, I think a custom class is almost a must.

Note that your custom class could use a BigDecimal internally to hold the amount, if it was a good match for what you actually need to do. If a long matches your model better, then go ahead with that.