Question

在我的驱动程序中，这一行给出了cannot find symbol错误，我不知道为什么。该方法在SavingsAccount类中明确定义，我可以参考我的驱动程序中的所有其他方法但不是那个，我尝试将类型更改为double等，但仍然无法正常工作

Account acct2 = new SavingsAccount (name);
acct2.calculateBalance();

SavingsAccount类继承自Account class：

public class SavingsAccount extends Account
{
    private final short minBalance = 0;
    private double overdraftFee;
    private double yearlyInterestRate = 0.02;
    private double interestAmount;

    public SavingsAccount (String name)
    {
        super(name);
    }

    public double withdraw (double amount)
    {
        if (accountBalance - amount >= minBalance)
        {
            accountBalance -= amount;
            System.out.print ("Withdraw Successful");
        }
        else 
        {
            accountBalance -= amount;
            overdraftFee = accountBalance * (0.10);
            accountBalance += overdraftFee;
            System.out.print ("Withdraw Succesful, however overdraft fee of 10% has been applied to your account");


        }

        return accountBalance;
    }

// ----------------- this is the method I try to invoke -----------------------------
    public void calculateBalance ()
    {
        interestAmount = (accountBalance * yearlyInterestRate);
        accountBalance += interestAmount;
    }
// ----------------------------------------------------------------------------------

    public String toString()
    {
        return super.toString() + " Interest Received: " + interestAmount;
    }


}

帐户类，如果需要

import java.util.Random;
import java.text.NumberFormat;

public abstract class Account
{
    protected double accountBalance;
    protected long accountNumber;
    protected String accountHolder;
    public Account (String name)
    {
        accountHolder = name;
        accountBalance = 0;
        Random accountNo = new Random();
        accountNumber  = accountNo.nextInt(100000);
    }

    public double deposit (double amount)
    {
        accountBalance += amount;

        return accountBalance;
    }

    public String toString()
    {
        NumberFormat accountBal = NumberFormat.getCurrencyInstance();
        return "Account Balance: " + accountBal.format(accountBalance) + "\nAccount Number: " + accountNumber;
    }

    public String getAccountHolder()
    {
        return accountHolder;
    }

    public double getAccountBalance()
    {
        return accountBalance;
    }

    public abstract double withdraw (double amount);

}

Answer 1

Account acct2 = new SavingsAccount (name);
acct2.calculateBalance();

这是因为虽然您有一个SavingsAccount对象，但您使用的是Account类型的引用变量，因此您只能访问Account类中的那些方法。

您的calculateBalance()课程中没有Account方法。

这就是为什么你无法访问它并且编译器抱怨它无法找到名为calculateBalance的方法，因为它看到引用类型是Account并且Account内没有这样的方法} class。

如果您想使用该方法，请将引用类型更改为SavingsAccount：

SavingsAccount acct2 = new SavingsAccount (name);

或者您可以在访问该方法时显式转换它

((SavingsAccount) acct2).calculateBalance();

但请注意，如果ClassCastException对象实际上不是acct2

的对象，它可以抛出SavingsAccount

<强>更新

但是请记住，在运行时，Java会动态使用虚方法调用根据实际实例选择将运行的方法的实际版本。

Answer 2

尝试切换，

Account acct2 = new SavingsAccount (name);
acct2.calculateBalance();

到

SavingsAccount acct2 = new SavingsAccount (name);
acct2.calculateBalance();

或（不确定为什么你会这样），我相信你可以将acct2投射到SavingsAccount。

Answer 3

“所有其他方法”来自Account，而不是SavingsAccount。当您想要致电cCalculateBalance时，请尝试这样：

(SavingsAccount)acct2.calculateBalance()

“找不到符号：方法”但声明了方法

3 个答案: