Exercise: Money operations
Implement appropriate operator methods in the class Money to allow:
- adding two
Moneyobjects using+operator, (in case of different currencies, throwIllegalArgumentException), - subtracting two
Moneyobjects using-operator, (in case of different currencies, throwIllegalArgumentException), - negating a
Moneyobject using unary-operator, - multiplying a
Moneyobject by an integer number using*operator.
Starting code:
data class Money(
val amount: BigDecimal,
val currency: Currency
) {
// TODO: Implement operators overloading here
companion object {
fun eur(amount: String) =
Money(BigDecimal(amount), Currency.EUR)
}
}
enum class Currency {
EUR, USD, GBP
}
The following code should work:
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
println(money1 + money2) // Money(amount=39.99, currency=EUR)
println(money2 - money1) // Money(amount=19.99, currency=EUR)
println(-money1) // Money(amount=-10.00, currency=EUR)
println(money1 * 3) // Money(amount=30.00, currency=EUR)
This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in essentials/operators/Money.kt. You can find there starting code, example usage and unit tests.
Once you are done with the exercise, you can check your solution here.
Playground
import org.junit.Test
import java.math.BigDecimal
import kotlin.test.assertEquals
data class Money(
val amount: BigDecimal,
val currency: Currency
) {
// TODO: Implement operators overloading here
companion object {
fun eur(amount: String) =
Money(BigDecimal(amount), Currency.EUR)
}
}
enum class Currency {
EUR, USD, GBP
}
fun main() {
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
println(money1 + money2) // Money(amount=39.99, currency=EUR)
println(money2 - money1) // Money(amount=19.99, currency=EUR)
println(-money1) // Money(amount=-10.00, currency=EUR)
println(money1 * 3) // Money(amount=30.00, currency=EUR)
}
class MoneyOperationsTest {
@Test
fun `Money can be added`() {
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
assertEquals(Money.eur("39.99"), money1 + money2)
}
@Test
fun `Money throws exception when adding different currencies`() {
for (currency in Currency.entries) {
for (otherCurrency in (Currency.entries - currency)) {
val money1 = Money(BigDecimal("10.00"), currency)
val money2 = Money(BigDecimal("29.99"), otherCurrency)
assertThrows<IllegalArgumentException> { money1 + money2 }
}
}
}
@Test
fun `Money can be subtracted`() {
val money1 = Money.eur("10.00")
val money2 = Money.eur("29.99")
assertEquals(Money.eur("19.99"), money2 - money1)
}
@Test
fun `Money throws exception when subtracting different currencies`() {
for (currency in Currency.entries) {
for (otherCurrency in (Currency.entries - currency)) {
val money1 = Money(BigDecimal("10.00"), currency)
val money2 = Money(BigDecimal("29.99"), otherCurrency)
assertThrows<IllegalArgumentException> { money1 - money2 }
}
}
}
@Test
fun `Money can be negated`() {
assertEquals(Money.eur("-10.00"), -Money.eur("10.00"))
assertEquals(Money.eur("-100.00"), -Money.eur("100.00"))
assertEquals(Money.eur("10.00"), -Money.eur("-10.00"))
assertEquals(Money.eur("-999.999"), -Money.eur("999.999"))
}
@Test
fun `Money can be multiplied by a number`() {
assertEquals(Money.eur("30.00"), Money.eur("10.00") * 3)
assertEquals(Money.eur("0.00"), Money.eur("10.00") * 0)
assertEquals(Money.eur("-30.00"), Money.eur("10.00") * -3)
}
}
inline fun <reified T: Throwable> assertThrows(operation: () -> Unit) {
val result = runCatching { operation() }
assert(result.isFailure) { "Operation has not failed with exception" }
val exception = result.exceptionOrNull()
assert(exception is T) { "Incorrect exception type, it should be ${T::class}, but it is $exception" }
}
