Question

我正在使用超类Account和子类SavingsAccount建立一个无法透支的银行帐户。从主类调用makeWithdrawal()方法时，应检查提取是否大于余额并提示输入，然后编辑余额。

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

Account中的方法：

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

（非常简单。）这种方法最初是抽象的，但却导致错误。

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

问题不在于您致电super.makeWithdrawl()，这是正确的。它位于上面return子句中的空if语句中。您获取更新提取金额的逻辑是明智的，但是当您这样做时需要返回新的余额。我建议只是将呼叫转移到条件之外的super.makeWithdrawl()：

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

如果原始提款金额太大，这将使用更新的提款金额。

Answer 2

if

中的

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

你需要返回双值而不是简单的返回。

Answer 3

问题在于

返回;

你应该用

替换它

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 4

如果我理解正确的话：

Account是基类而SavingsAccount是子类？

然后：super.makeWithdrawal(withdrawal);

还要确保在定义类时继承：

public class SavingsAccount extends Account{...}

从子类调用超类方法

4 个答案: