javaLogic errorMedium

Unexpected rounding error in financial calculation

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What it should do

Calculate the total amount after applying a tax rate. Example: calculateTotal(100, 0.18) -> 118.00

What happens instead

The calculated total amount is slightly off by a few decimal places.

import java.math.BigDecimal;

public class FinancialCalculator {
    public static BigDecimal calculateTotal(double amount, double taxRate) {
        BigDecimal tax = new BigDecimal(amount * taxRate);
        BigDecimal total = new BigDecimal(amount).add(tax);
        return total.setScale(2, BigDecimal.ROUND_HALF_UP);
    }
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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import java.math.BigDecimal; public class FinancialCalculator { public static BigDecimal calculateTotal(double amount, double taxRate) { BigDecimal tax = new BigDecimal(amount * taxRate); BigDecimal total = new BigDecimal(amount).add(tax); return total.setScale(2, BigDecimal.ROUND_HALF_UP); } }

Unexpected rounding error in financial calculation

What it should do

What happens instead

More logic errors to practise

Unexpected rounding error in financial calculation

What it should do

What happens instead

More logic errors to practise