The need for BigDecimal

Tim McKenna

Seneca@York

Why BigDecimal?

BigDecimal provides exact decimal values

doubles only approximate decimals use BigDecimal for money and

business calculations yes, doubles are easier no, you cannot use doubles

BigDecimal vs double

from an assignment that didn’t use BigDecimal…Type Vegan Survey Last Date RestaurantCode Y/N Amount Surveyed Name, LocationCF Y 3.59 2003-07-04 Blueberry Hill, YLM

Please enter survey amount (+ add, - subtract) > -3.59

Unable to subtract this amount -3.589999999999999857891452847979962825775146484375

because there is only 3.589999999999999857891452847979962825775146484375 left!

If you don't believe me…

from the IBM computer scientist who wrote the new, improved BigDecimal class: Using Java 5.0 BigDecimaland Decimal Arithmetic FAQ

Core Java Technologies Tech Tips:The need for BigDecimal

The BigDecimal Class

98.7% of numeric data in business applications has a predetermined number of decimals: currency, exchange rates, unit costs, discounts, taxes precision: digits in number including decimals scale: number of decimal places

JDBC maps DB decimal fields to BigDecimal BigD class provides control of rounding behaviour Examples: PaySchedule.java, PaySchedule2.java,

DontUseDouble.java

BigDecimal add & subtract

BigDecimal sum, difference, …; // note: immutable class

sum = addend.add(augend); // a = b + c

sum = sum.add(anotherBigDecimal); // a += d

difference = minuend.subtract(subtrahend); // a = b - c

BigDecimal multply & divide

import static java.math.RoundingMode.HALF_UP;// standard rounding, import the constant

BigDecimal product, quotient; // immutable product = multiplicand.multiply(factor); product = // round result to 2 decimals

product.setScale(2, HALF_UP); product = // multiply and round

multiplicand.multiply(factor).setScale(2, HALF_UP); quotient = // round result to 2 decimals

dividend.divide(divisor, 2, HALF_UP);

BigDecimal comparisons

import static java.math.BigDecimal.ZERO; payment.compareTo(interest) > 0

"if payment is greater than interest " principal.compareTo(payment) <= 0

"if principal is less than/equal to payment" principal.compareTo(ZERO) == 0

"if principal is equal to zero" principal.equals(ZERO)

…may not be what you mean. see API.