通过方法继承和传递参数

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部分遇到了问题。对于初学者来说，这不是独立代码。这是银行账户计划的一大部分。 '出纳'部分是实际运行的代码。

我的问题是我无法获得'SavingsAccount'来清理编译。我没有办法尝试第5部分的作品。它说它不能读取符号，但我不确定它究竟有多严重。我也编译了'teller'文件，但是如果没有一些错误就不会编译。最重要的是，它无法找到我首先没有触及的课程和符号。我不确定这是否是由于我没有使用SavingsAccount进行干净编译。编译器错误：Activity-10-1 \ SavingsAccount.java：68：error：找不到符号 deposit（getBalance（）*（interestRate/12.0））; ^ 符号：方法为getBalance（） 位置：类SavingsAccount 1错误

工具退出码1

Answer 1

你需要得到第1步之前完成第5步将工作完成。按照原样，SavingsAccount继承自Object，而不是从BankAccount继承。尝试改变

public class SavingsAccount 

到

public class SavingsAccount extends BankAccount 

在这一点上，getBalance()方法（我猜在BankAccount类中定义）应该成为访问。