BigDecimal 包装器：具有零静态字段

Question

我的自定义类是和类Money的一种包装。BigDecimalorg.joda.money.Money

与之前一样BigDecimal，我需要Money.ZERO在我的应用程序中使用 a （通常在reduce()操作中）。

我发现我Money.ZERO在应用程序执行期间的更改（它的amount值可能非零）导致无效结果。

下面是我的自定义Money类：

@Getter

@Embeddable

@NoArgsConstructor(access = AccessLevel.PRIVATE)

@AllArgsConstructor(access = AccessLevel.PRIVATE)

public class Money implements Serializable {

    private static final long serialVersionUID = -4274180309004444639L;

    public static final Money ZERO = new Money(BigDecimal.ZERO, CurrencyUnit.EUR);

    private BigDecimal amount;

    @Convert(converter = CurrencyUnitToStringConverter.class)

    private CurrencyUnit currency;

    public static Money of(BigDecimal amount, CurrencyUnit currency) {

        return new Money(amount, currency);

    }

    public Money add(Money addition) {

        checkCurrency(addition);

        amount = amount.add(addition.getAmount());

        return new Money(amount, currency);

    }

    public Money substract(Money reduction) {

        checkCurrency(reduction);

        amount = amount.subtract(reduction.getAmount());

        return new Money(amount, currency);

    }

    private void checkCurrency(Money other) {

        if (!Objects.equal(getCurrency(), other.getCurrency())) {

            throw new IllegalArgumentException("Currency does not match when adding amounts!");

        }

    }

所以我的目标是拥有一个ZERO数量BigDecimal.ZERO永远保持不变的领域。

Answer 1

您正在修改内部状态。看看你的add方法：public Money add(Money addition) {    checkCurrency(addition);    amount = amount.add(addition.getAmount());    return new Money(amount, currency);}在此方法中，您将重新分配amount，从而更改当前实例的值Money。这是一个简单的修复：public Money add(Money addition) {    checkCurrency(addition);    BigDecimal newAmount = amount.add(addition.getAmount());    return new Money(newAmount, currency);}这同样适用于你的substract方法。