Item 48 - Avoid float and double if exact answers are required

From Effective Java 2/e by Joshua Bloch

• The float and double types are particularly ill-suited for monetary calculations
• Use BigDecimal, int, or long for monetary calculations

Using double and float

// Broken - uses floating point for monetary calculation!
public static void main(String[] args) {
   double funds = 1.00;
   int itemsBought = 0;
   for (double price = .10; funds >= price; price += .10) {
      funds -= price;
      itemsBought++;
   }
   System.out.println(itemsBought + " items bought.");
   System.out.println("Change: $" + funds); // $0.3999999999999999
}

Using BigDecimal

public static void main(String[] args) {
   final BigDecimal TEN_CENTS = new BigDecimal( ".10");
   int itemsBought = 0;
   BigDecimal funds = new BigDecimal("1.00");
   for (BigDecimal price = TEN_CENTS; funds.compareTo(price) >= 0; price = price.add(TEN_CENTS)) {
      itemsBought++;
      funds = funds.subtract(price);
   }
   System.out.println(itemsBought + " items bought.");
   System.out.println("Money left over: $" + funds); // $0.00
}

Using int

public static void main(String[] args) {
   int itemsBought = 0;
   int funds = 100;
   for (int price = 10; funds >= price; price += 10) {
      itemsBought++;
      funds -= price;
   }
   System.out.println(itemsBought + " items bought.");
   System.out.println("Money left over: "+ funds + " cents"); // 0
}

Posted by The Finest Artist