从子类调用超类方法

Question

我正在用一个超类Account和一个不能透支的子类SavingsAccount来建模一个银行帐户。当从主类调用时，makeWithdrawal()方法应该检查取款是否大于输入的余额和提示，然后编辑余额。

我如何从makeWithdrawal()调用Account方法并在SavingsAccount中使用Super关键字覆盖它？我的编译器给我“错误:不兼容类型:缺少返回值”。

Account中的方法

double makeWithdrawal(double withdrawal)    {
    return balance -= withdrawal;
}

(很简单)这个方法最初是抽象的，但它导致了错误。

SavingsAccount中的方法

    public double makeWithdrawal(double withdrawal) {
        double tempbalance = getBalance();
        if (withdrawal > getBalance())  {
            withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
            return;
        }
        else    {
            return super.makeWithdrawal(withdrawal);
            }
    }

Answer 1

问题在于

返回；

你应该把它换成

退货退货；

    public double makeWithdrawal(double withdrawal) {
    double tempbalance = getBalance();
    if (withdrawal > getBalance())  {
        withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
        return withdrawal;
    }
    else    {
        return super.makeWithdrawal(withdrawal);
        }
}

Answer 2

问题不在于您调用super.makeWithdrawl()，这是正确的。它带有上面的return子句中的空if语句。您的逻辑得到更新提取金额是明智的，但您需要返回新的余额时，您这样做。我建议将调用移到条件之外的super.makeWithdrawl()：

if(withdrawal > getBalance())  {
    withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
}
return super.makeWithdrawal(withdrawal);

如果原来的提款金额太大，这将使用更新的提款金额。

Answer 3

如果

if (withdrawal > getBalance())  {
            withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
            return;
        }

您需要返回双值，而不是简单的返回。