java - 继承和通过方法传递参数

Question

import java.text.NumberFormat;

// 1. ***** indicate that SavingsAccount inherits
//          from BankAccount
public class SavingsAccount
{

public final double DEFAULT_RATE = .03;

// 2. ****** define the private interestRate instance variable
// interestRate, a double, represents an annual rate
// Part 2 student code starts here:
    private double interestRate;



// Part 2 student code ends here.

// 3 ***** write the default constructor
/** default constructor
*   explicitly calls the BankAccount default constructor
*   set interestRate to default value DEFAULT_RATE
*   print a message to System.out indicating that
*    constructor is called
*/
// Part 3 student code starts here:
    public void BankAccount()
    {
        interestRate = DEFAULT_RATE;
        System.out.println("Default constructor is called. ");
    }


// Part 3 student code ends here.

// 4 ***** write the overloaded constructor
/** overloaded constructor
*   explicitly call BankAccount overloaded constructor
*   call setInterestRate method, passing startInterestRate
*   print a message to System.out indicating that
*    constructor is called
*  @param  startBalance      starting balance
*  @param  startInterestRate starting interest rate
*/
// Part 4 student code starts here:

    public void BankAccount(double startBalance,double startInterestRate)
    {

        setInterestRate(startInterestRate);
        System.out.println("Overloaded constructor is called. ");
    }
        // Part 4 student code ends here.

// 5 ****** write this method:
/** applyInterest method, no parameters, void return value
*  call deposit method, passing a month's worth of interest
*  remember that interestRate instance variable is annual rate
*/
// Part 5 student code starts here:

    public void applyInterest()
    {
        deposit ( super.getBalance() * (interestRate / 12.0));
    }

// Part 5 student code ends here.

/** accessor method for interestRate
*  @return  interestRate
*/
public double getInterestRate()
{
  return interestRate;
}

/** mutator method for interestRate
*  @param  newInterestRate new value for interestRate
*          newInterestRate must be >= 0.0
*            if not, print an error message
*/
public void setInterestRate(double newInterestRate)
{
  if (newInterestRate >= 0.0)
  {
    interestRate = newInterestRate;
  }
  else
  {
    System.err.println("Interest rate cannot be negative");
  }
}

// 6 *****  write this method
/* toString method
*  @return String containing formatted balance and interestRate
*    invokes superclass toString to format balance
*    formats interestRate as percent using a NumberFormat object
*    To create a NumberFormat object for formatting percentages
*    use the getPercentInstance method in the NumberFormat class,
*    which has this API:
*       static NumberFormat getPercentInstance( )
*/
// Part 6 student code starts here:

    public String toString()
    {
      NumberFormat percent = NumberFormat.getPercentInstance();
      return super.toString()
        + "\n" + "interestRate is " + percent.format(interestRate);
    }

// Part 6 student code ends here.

}

到目前为止，我在第 5 部分中遇到了麻烦。对于初学者来说，这不是独立的代码。它是银行账户计划的较大部分。 “teller”部分是实际运行的代码。

我的问题是我无法让“SavingsAccount”进行干净编译。我为第 5 部分尝试的流程没有成功。它说它无法读取该符号，但我不确定它到底错在哪里。我还编译了“teller”文件，但编译时会出现一些错误。最大的问题是它找不到我一开始没有接触过的类和符号。我不确定这是否是因为我没有让 SavingsAccount 干净地编译。

编译器错误:Activity-10-1\SavingsAccount.java:68:错误:找不到符号 存款 (getBalance() * (利率/12.0)); ^ 符号:方法 getBalance() 位置:类 SavingsAccount1 个错误

工具已完成，退出代码为 1

Answer 1

您需要先完成第 1 步，然后第 5 步才能发挥作用。就目前情况而言，SavingsAccount 继承自 Object，而不是BankAccount。尝试改变

public class SavingsAccount

至

public class SavingsAccount extends BankAccount

此时，getBalance() 方法(我猜测是在 BankAccount 类中定义的)应该可以访问。