Java问题与正确更新变量

Question

I have the following Account class which is the super class of CurrentAccount . I am however having issues when I create an instance of each class. The currentAccount should take away 6 as a charge if the balance is below 100 but its taking away 3. I'm obviously missing a deceleration somewhere.

public class Account {

    private String name;
    private double balance;
    public double initDeposit;
    public double threshold = 100.00;
    public final double fee = 3.00;

    public Account(String name, double initDeposit) {
        this.balance = initDeposit;
        this.name = name;
    }

    public void deposit(double amount) {
        setBalance(amount);
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double amount) {
        balance += amount;
    }

    public void withdraw(double amount) {
        if (getBalance() < 100 && getBalance() >= -50) {
            balance = balance - amount - fee;
        } else {
            balance = balance - amount;
        }
    }

    public String toString() {
        String s = "Name: " + name + "\n" + "Balance: " + balance;
        return s;
    }
}

---

public class CurrentAccount extends Account {

    private String name;
    private double balance;
    public double initDeposit;
    public double threshold = 100.00;
    public final double fee = 6.00;

    public CurrentAccount(String name, double initDeposit) {
        super(name, initDeposit);
    }
}

Answer 1

In Java, instance variables do not replace or override the same named variable in a superclass. If you declare a same-named variable in a subclass, now you have two variables, not one. Just because you declared another fee in CurrentAccount doesn't mean the code in Account will use the fee in CurrentAccount -- it can't.

To apply the different behavior you need, declare a method called getFee() in Account returning a double that can be overridden in CurrentAccount to change the behavior.

In Account:

public double getFee() { return 3.00; }

In CurrentAccount:

@Override
public double getFee() { return 6.00; }

Then call getFee() whenever you need to reference the fee, instead of referring to fee .