我正在做一项关于java中继承的家庭作业。我在理解如何从子类访问超类中的数组时遇到了一点困难。我看了其他几个问题，由于我是java的新手，我仍然不太明白
这是特级
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++) {
}
}
}
最后的循环是事情有点混乱的地方。Netbeans抛出错误，说"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
谢谢你抽出时间！
编辑
这里是相同作业的延续
谢谢大家的回复，你的建议解决了这个问题，不过我现在又遇到了一个减速带。for循环所在的这个方法背后的想法是运行BankAccount对象的数组，检查它们中是否有InterestAccount类型的（我以前构建的一个类），如果是，则从该类调用yearlyUpdate（）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;
}
}
这是我目前与合作的超级课程
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，这是我试图为循环运行这个的子类
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"working"上调用"yearlyUpdate（）"方法时找不到它。我不明白的是，由于之前的代码验证了工作对象是InterestAccount类型的，它应该有可用的方法
谢谢你的帮助！
// Other methods
public double endOfYear() {
for (i=0;i<BankAccount.length();i++) {
}
}
您需要申报i
// Other methods
public double endOfYear() {
for (int i=0;i<BankAccount.length();i++) {
}
}
在循环中，变量i未声明。此外，由于我认为您希望循环通过数组中的帐户，我认为您应该使用以下内容：
for(int i = 0; < numberOfAccounts; i++)
{
BankAccount bankAccount = myAccounts[i];
// other stuff
}
就像错误所说的：i是未定义的。
尝试：
for (int i=0;i<BankAccount.length();i++)
我猜这仍然很糟糕，因为你想要的是数组的长度，而不是BankAccount类（可能未定义）
for (int i=0;i<myAccounts.length();i++)
对于错误，您需要在BankSubClass.endOfYear中使用变量i之前定义变量i。该语句应该是
for (int i=0;i<BankAccount.length();i++)
您没有在for循环中声明i
for (int i=0;i<BankAccount.length();i++)