Java从子类访问 protected 变量

Question

我正在做一个关于 java 继承的家庭作业。我在理解如何从子类访问父类(super class)中的数组时遇到了一些麻烦。我查看了其他几个问题，但由于我对 Java 还很陌生，所以我还是不太明白。

这是父类(super class)

import java.text.NumberFormat;

/**
 * Bank represents a single Bank containing a number of BankAccounts.
 */
public class Bank {

    // Member variables:

    /** The array of BankAccount objects contained in this bank. */
    protected BankAccount[] myAccounts = new BankAccount[2000];

    /** The number of BankAccount objects stored in the array in this bank. */
    protected int numberOfAccounts = 0;


    // Constructors:

    /**
     * Creates a Bank.
     */
    public Bank() {}


    // Methods:

    /** 
     * Creates an account with the name and balance, and adds it to 
     * the bank's list of accounts.
     * If the name already exists, no account will be created.
     * @param aName The name for the new account.
     * @param aBalance The initial balance for the new account.
     */
    public void createAccount( String aName, double aBalance) {
        BankAccount existing = this.findAccount( aName);
        if( existing != null) return;
        BankAccount anAccount = new BankAccount( aBalance, aName);
        this.myAccounts[ numberOfAccounts] = anAccount;
        this.numberOfAccounts++;
    }

    /** 
     * Finds an account in the bank's list of accounts by name.
     * If no account is found, this method returns null.
     * @param aName The name of the BankAccount to search for.
     * @return The BankAccount bearing the given name, if found.
     */
    public BankAccount findAccount( String aName) {
        BankAccount answer = null;
        for( int index = 0; index < numberOfAccounts; index++) {
            BankAccount anAccount = this.myAccounts[ index];
            if( aName.equals( anAccount.getName())) {
                return( anAccount);
            }
        }
        return( answer);
    }

    /** 
     * Returns a String which represents a short summary of 
     * all the accounts in the bank.
     * @return A String representation of all accounts and their balances in the bank.
     */
    public String toString() {
        String answer = "";
        NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance();
        for( int index = 0; index < numberOfAccounts; index++) {
            BankAccount anAccount = this.myAccounts[ index];
            String money = currencyFormatter.format( anAccount.getBalance());
            answer += anAccount.getName() + " \t" + money + "\n";
        }
        return( answer);
    }

}

这是子类的开始

public class BankSubClass extends Bank{
    private double interestPaid;

    // Constructor
    public BankSubClass(String aName, double aBalance, double aInterest) {
        super();
        this.interestPaid = aInterest;
    }

    // Getters
    public double getInterestPaid() {return(this.interestPaid);}

    // Setters
    public void setInterestPaid(double setInterestPaid) {this.interestPaid = setInterestPaid;}

    // Other methods
    public double endOfYear() {
        for (i=0;i<BankAccount.length();i++) {

        }
    }

}

末尾的 for 循环有点出问题了。 Netbeans 抛出错误提示“找不到符号:变量 i”。也许这与我尝试使用的银行帐户数组无关，我不知道。非常感谢任何帮助

感谢您的宝贵时间!

编辑

所以这里是相同作业的延续

感谢大家的回复，您的建议解决了这个问题，但我目前正在遇到另一个减速带。 for 循环所在方法背后的想法是遍历 BankAccount 对象数组，检查它们是否属于 InterestAccount 类型(我之前构建的类)，如果是，则调用 yearlyUpdate()该类的方法

这是 InterestAccount 类

public class InterestAccount extends BankAccount {
    private double interestRate;

    // Constructor
    /**
     * Create and interest bearing bank account with a balance, name,
     * and interest rate
     * @param aBalance The balance of the account
     * @param aName The name tied to the account
     * @param myInterestRate The interest rate of the account
     */
    public InterestAccount(double aBalance, String aName, double myInterestRate) {
        super(aBalance, aName);
        this.interestRate = myInterestRate;
    }

    // Getters
    /**
     * Gets the interest rate of the account
     * @return the interest rate of the account
     */
    public double getInterestRate() {return(this.interestRate);}

    // Setters
    /**
     * Sets the interest rate of the account
     * @param interestSet The new interest rate of the account
     */
    public void setInterestRate(int interestSet) {this.interestRate = interestSet;}

    // Other Methods
    /**
     * Calculates the interest earned on the account over a year
     * @return the interest earned over a year
     */
    public double yearlyUpdate() {
        double answer = (super.getBalance()*this.interestRate);
        return answer;
    }
}

这是我目前正在使用的父类(super class)

import java.text.NumberFormat;

/**
 * Bank represents a single Bank containing a number of BankAccounts.
 */
public class Bank {

    // Member variables:

    /** The array of BankAccount objects contained in this bank. */
    protected BankAccount[] myAccounts = new BankAccount[2000];

    /** The number of BankAccount objects stored in the array in this bank. */
    protected int numberOfAccounts = 0;


    // Constructors:

    /**
     * Creates a Bank.
     */
    public Bank() {}


    // Methods:

    /** 
     * Creates an account with the name and balance, and adds it to 
     * the bank's list of accounts.
     * If the name already exists, no account will be created.
     * @param aName The name for the new account.
     * @param aBalance The initial balance for the new account.
     */
    public void createAccount( String aName, double aBalance) {
        BankAccount existing = this.findAccount( aName);
        if( existing != null) return;
        BankAccount anAccount = new BankAccount( aBalance, aName);
        this.myAccounts[ numberOfAccounts] = anAccount;
        this.numberOfAccounts++;
    }

    /** 
     * Finds an account in the bank's list of accounts by name.
     * If no account is found, this method returns null.
     * @param aName The name of the BankAccount to search for.
     * @return The BankAccount bearing the given name, if found.
     */
    public BankAccount findAccount( String aName) {
        BankAccount answer = null;
        for( int index = 0; index < numberOfAccounts; index++) {
            BankAccount anAccount = this.myAccounts[ index];
            if( aName.equals( anAccount.getName())) {
                return( anAccount);
            }
        }
        return( answer);
    }

    /** 
     * Returns a String which represents a short summary of 
     * all the accounts in the bank.
     * @return A String representation of all accounts and their balances in the bank.
     */
    public String toString() {
        String answer = "";
        NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance();
        for( int index = 0; index < numberOfAccounts; index++) {
            BankAccount anAccount = this.myAccounts[ index];
            String money = currencyFormatter.format( anAccount.getBalance());
            answer += anAccount.getName() + " \t" + money + "\n";
        }
        return( answer);
    }

}

最后，这是我尝试在其中运行此 for 循环的子类

public class BankSubClass extends Bank{
    private double interestPaid;

    // Constructor
    public BankSubClass(String aName, double aBalance, double aInterest) {
        super();
        this.interestPaid = aInterest;
    }

    // Getters
    public double getInterestPaid() {return(this.interestPaid);}

    // Setters
    public void setInterestPaid(double setInterestPaid) {this.interestPaid = setInterestPaid;}

    // Other methods
    public double endOfYear() {
        double trackInterest=0;
        for (int i=0;i<numberOfAccounts;i++) {
            BankAccount working = myAccounts[i];
            boolean hasInterest = working instanceof InterestAccount;
            if (hasInterest) {
                trackInterest = trackInterest + working.yearlyUpdate();
            }
            return trackInterest;
        }
    }

}

目前 netbeans 在尝试在“工作”时调用它时找不到“yearlyUpdate()”方法我不理解的是，因为以前的代码验证了工作对象是 InterestAccount 类型，它应该有该方法可用

感谢您的帮助!

Answer 1

// Other methods
public double endOfYear() {
    for (i=0;i<BankAccount.length();i++) {

    }
}

你需要声明i

// Other methods
public double endOfYear() {
    for (int i=0;i<BankAccount.length();i++) {

    }
}