从子类调用超类方法

Question

我正在用一个不能透支的 superclass Account 和 subclass SavingsAccount 模拟一个银行账户。 makeWithdrawal() 方法，当从主 class 调用时，应该检查取款是否大于余额并提示输入，然后编辑余额。

如何从 Account 调用 makeWithdrawal() 方法并使用 super 关键字在 SavingsAccount 中覆盖它？我的编译器给我“错误：不兼容的类型：缺少 return 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

如果我理解正确的话：

Account 是基础 class 而 SavingsAccount 是子class?

然后：super.makeWithdrawal(withdrawal);

还要确保在定义 class 时继承：

public class SavingsAccount extends Account{...}

Answer 2

问题不在于您对 super.makeWithdrawl() 的调用，这是正确的。它与上面 if 子句中的空 return 语句一起使用。您获取提款金额更新的逻辑是明智的，但是您需要 return 执行此操作时的新余额。我建议将调用移至 super.makeWithdrawl() 条件之外：

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，这将使用更新后的提款金额。

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 return 双倍值而不是简单 returning。

Answer 4

问题出在

return;

您应该将其替换为

return withdrawal;

    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);
        }
}

从子类调用超类方法

Calling a superclass method from a subclass

java

inheritance

subclass

bank

superclass