Java 從子類訪問受保護的變量

Question

我正在做一項家庭作業，查看 java 中的 inheritance。我在理解如何從子類訪問超類中的數組時遇到了一些麻煩。 我查看了其他幾個問題，由於我對 java 還很陌生，所以我還是不太明白。

這里是超級 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);
    }

}

這是子類的開始

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++) {

        }
    }

}

最后的 for 循環是事情變得有點絆倒的地方。 Netbeans 拋出錯誤“找不到符號：變量 i”。 也許這與我嘗試使用的銀行帳戶數組無關，我不知道。 任何幫助深表感謝

謝謝你的時間！

編輯

所以這是相同作業的延續

感謝大家的回復，您的建議解決了這個問題，但是我目前正在遇到另一個減速帶。 for 循環所在方法背后的想法是遍歷 BankAccount 對象數組，檢查它們是否屬於 InterestAccount 類型（我之前構建的 class），如果是，則調用 yearlyUpdate()來自 class 的方法

這是 InterestAccount class

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;
    }
}

這是我目前正在使用的超級 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，這是我試圖在其中運行此 for 循環的子類

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;
        }
    }

}

currently.netbeans 在嘗試在“工作”時調用它時找不到“yearlyUpdate()”方法我不理解的是，因為前面的代碼驗證了工作 object 是 InterestAccount 類型，它應該有那個方法可用的

謝謝您的幫助！

Answer 1

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

    }
}

你需要聲明i

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

    }
}

Answer 2

就像錯誤所說：我是未定義的。

嘗試：

for (int i=0;i<BankAccount.length();i++)

我猜這仍然很糟糕，因為你想要數組的長度，而不是 BankAccount class（可能未定義）

for (int i=0;i<myAccounts.length();i++)

Answer 3

對於錯誤，您需要在 BankSubClass.endOfYear 中使用它之前定義變量 i。 聲明應該是

for (int i=0;i<BankAccount.length();i++)

Answer 4

你沒有在 for 循環中聲明i

for (int i=0;i<BankAccount.length();i++)

Answer 5

在您的循環中，變量i未聲明。 此外，由於我認為您希望遍歷數組中的帳戶，因此我認為您應該使用以下內容：

for(int i = 0; < numberOfAccounts; i++)
{
    BankAccount bankAccount = myAccounts[i];
    // other stuff
}