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.

}

So far, I am having trouble with part 5. For starters, this is not stand alone code. It is a larger part of a bank account program. The 'teller' part is the code that is actually run.

My problem is I cannot get 'SavingsAccount' to clean compile. No process I try for part 5 works. It says it cannot read the symbol, but I'm not sure how exactly it can be wrong. I also compiled the 'teller' file, but it won't compile without quite a few errors. The biggest being that it can't find classes and symbols that I haven't touched in the first place. I'm not sure if that is due to the fact I haven't got SavingsAccount to compile cleanly or not.

COMPILER ERROR: Activity-10-1\\SavingsAccount.java:68: error: cannot find symbol deposit (getBalance() * (interestRate / 12.0)); ^ symbol: method getBalance() location: class SavingsAccount 1 error

Tool completed with exit code 1

Answer 1

You need to get step 1 done before step 5 will work. As it stands, SavingsAccount inherits from Object , not from BankAccount . Try changing

public class SavingsAccount

to

public class SavingsAccount extends BankAccount

At that point, the getBalance() method (which I'm guessing is defined in the BankAccount class) should become accessible.