“找不到符号：方法”但声明了方法

Question

In my driver program, this line gives me cannot find symbol error and I don't know why. The method is clearly defined in the SavingsAccount class, and I can refer to all other methods in my driver program but just not that one, I tried changing the type to double , and etc but still not working.

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

SavingsAccount class inherits from 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;
    }


}

Account class, if needed

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();

This is because although you have an object of SavingsAccount you are using refrence variable of type Account so you can access only those methods that are there in Account class.

And you don't have calculateBalance() method in your Account class.

That's why you are not able to access it and compiler complains that it cannot find a method named calculateBalance as it sees that reference type is Account and there is no such method inside Account class.

If you want to use that method then change reference type to SavingsAccount :

SavingsAccount acct2 = new SavingsAccount (name);

Or you can explicitly cast it when accessing that method

((SavingsAccount) acct2).calculateBalance();

but be alert that it can throw ClassCastException if acct2 object is actually not an object of SavingsAccount

UPDATE:

But remember that at runtime, Java uses virtual method invocation to dynamically select the actual version of the method that will run, based on the actual instance.

Answer 2

Try switching,

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

To

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

Or (Not sure why you would want to), I believe you could cast acct2 to SavingsAccount .

Answer 3

"All other methods" are coming from Account , not SavingsAccount . When you are wanting to call cCalculateBalance , try it like this:

(SavingsAccount)acct2.calculateBalance()