Item Avoid float and double if exact answers are required
Problem with float and double:
- Designed for scientific and mathematical calculations, perform binary floating point arithmetic.
- Not suitable for monetary calculations or situations that require exact answers.
- They cannot accurately represent negative powers of ten, such as 0.1, which leads to errors.
Example 1:
Incorrect calculation when subtracting dollar amounts:
System.out.println(1.03 - 0.42); // Resultado: 0.6100000000000001
Example 2:
Error when purchasing nine items for 10 cents each:
System.out.println(1.00 - 9 * 0.10); // Resultado: 0.09999999999999998
Even rounding, errors persist.
Problem with progressive calculations, such as when purchasing sweets at incremental prices of 0.10 to 1.00.
Example 3:
Mistake when buying sweets until you have no more money:
double funds = 1.00;
for (double price = 0.10; funds >= price; price += 0.10) {
funds -= price;
}
System.out.println(funds); // Resultado: 0.3999999999999999
Solution 1: Use BigDecimal
- Ideal for financial calculations and situations where precision is essential.
- Avoid using BigDecimal's double constructor, preferring the String constructor.
Example with BigDecimal:
BigDecimal funds = new BigDecimal("1.00");
BigDecimal price = new BigDecimal("0.10");
int itemsBought = 0;
while (funds.compareTo(price) >= 0) {
funds = funds.subtract(price);
price = price.add(new BigDecimal("0.10"));
itemsBought++;
}
System.out.println(itemsBought + " items bought. Money left: " + funds);
// Resultado: 4 items bought. Money left: 0.00
The calculation is now precise.
Disadvantages of BigDecimal:
- Less convenient to use than primitive types.
- Slower, especially for large volumes of operations.
Solution 2: Use int or long
- To avoid accuracy problems, do calculations in cents, using int or long instead of dollars with double.
Example with int (in cents):
int funds = 100; // 1.00 dólar = 100 centavos
int price = 10; // 0.10 dólar = 10 centavos
int itemsBought = 0;
while (funds >= price) {
funds -= price;
price += 10;
itemsBought++;
}
System.out.println(itemsBought + " items bought. Money left: " + funds);
// Resultado: 4 items bought. Money left: 0
The calculation is fast and accurate.
Conclusion:
- Do not use float or double for calculations that require exact precision.
- Use BigDecimal for monetary calculations or situations that require decimal precision.
- Use int or long for financial calculations that do not involve large numbers, doing the calculations in cents.
Choices:
- For up to 9 digits, use int.
- For up to 18 digits, use long.
- For larger quantities, use BigDecimal.
- This summary shows that, depending on the context, choosing between BigDecimal, int or long can optimize both precision and performance.
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