BigDecimal

In this chapter you will learn:

When to use BigDecimal
Why BigDecimal is good for monetary values

BigDecimal class

BigDecimal represents immutable, arbitrary-precision signed decimal numbers.

BigDecimal is useful for monetary values. The following code shows that floating-point-based invoice calculations leading to confusing results.

import java.text.NumberFormat;
//from ja  v  a  2  s  .c om
public class Main {
  public static void main(String[] args) {
    double total = 123.45;
    double discount = total * 0.01;
    double beforeTax = total - discount;
    double salesTax = beforeTax * 0.13;
    double result = beforeTax + salesTax;
    NumberFormat currencyFormat = NumberFormat.getCurrencyInstance();
    System.out.println("Subtotal: " + currencyFormat.format(total));
    System.out.println("Discount: " + currencyFormat.format(discount));
    System.out.println("SubTotal after discount: " + currencyFormat.format(beforeTax));
    System.out.println("Sales Tax: " + currencyFormat.format(salesTax));
    System.out.println("Total: " + currencyFormat.format(result));
  }
}

The output:

BigDecimal and monetary values

Never using float or double to represent monetary values.

The following code uses BigDecimal to do the invoice calculations

import java.math.BigDecimal;
import java.math.RoundingMode;
/*from  j  av a 2s .  co  m*/
public class Main {
  public static void main(String[] args) {
    BigDecimal total = new BigDecimal("123.45");
    BigDecimal discountPercent = new BigDecimal("0.10");
    BigDecimal discount = total.multiply(discountPercent);
    discount = discount.setScale(2, RoundingMode.HALF_UP);
    BigDecimal beforeTax = total.subtract(discount);
    beforeTax = beforeTax.setScale(2, RoundingMode.HALF_UP);
    BigDecimal salesTaxPercent = new BigDecimal("0.05");
    BigDecimal salesTax = beforeTax.multiply(salesTaxPercent);
    salesTax = salesTax.setScale(2, RoundingMode.HALF_UP);
    BigDecimal result = beforeTax.add(salesTax);
    result = result.setScale(2, RoundingMode.HALF_UP);
    System.out.println("Subtotal: " + total);
    System.out.println("Discount: " + discount);
    System.out.println("SubTotal after discount: " + beforeTax);
    System.out.println("Sales Tax: " + salesTax);
    System.out.println("Total: " + result);
  }
}