Help code problem please

[dannygirl sylvest]

I created a SavingsAccount class that's suppose to calculate a monthly interest rate (based off whatever the annual is inputed by user) and then add it to the balance and to a totalInterest accumulator. For some reason my formula keeps dividing instead of multiplying and i can't figure out why? Any ideas?
here's my work:


package assignment06;

/* Design a SavingsAccount class that stores a savings account's annual
* interest and balance.
*
*

 @author Dsylvester
 */
 class SavingsAccount
 {
       
    private double balance ;              // Account balance
    private double annualinterestrate;   // Annual interest rate
    
// add code to the constructors
public SavingsAccount()
{
    balance = 0.0;
    annualinterestrate = 0.0;

   
}
public SavingsAccount(double startBalance, double AnnualInterestRate)
{
    balance = startBalance;
    annualinterestrate = AnnualInterestRate;
}
 private double MonthlyInterestRate( double annualrate)
{
        return annualrate / 12 ;
        
}

public double calculateInterest(double monthlyrate)
{
    annualinterestrate = balance *monthlyrate;
    return annualinterestrate;
}





// use the public methods from class BankAccount for deposit/withdrawal
 // End class SavingsAccount

 /**
      The deposit method makes a deposit into
      the account.
      @param str The amount to add to the
                 balance field, as a String.
   */


  public void deposit(double addeposit)
   {
      balance += addeposit;
   }

   /**
      The withdraw method withdraws an amount
      from the account.
      @param amount The amount to subtract from
                    the balance field.
   */

   public void withdraw(double amount)
   {
      balance -= amount;
   }

   /**
      The withdraw method withdraws an amount
      from the account.
      @param str The amount to subtract from
                 the balance field, as a String.
   */

   public void withdraw(String str)
   {
      balance -= Double.parseDouble(str);
   }

   /**
      The setBalance method sets the account balance.
      @param b The value to store in the balance field.
   */

   public void setBalance(double b)
   {
      balance = b;
   }

   /**
      The setBalance method sets the account balance.
      @param str The value, as a String, to store in
                 the balance field.
   */

   public void setBalance(String str)
   {
      balance = Double.parseDouble(str);
   }

   /**
      The getBalance method returns the
      account balance.
      @return The value in the balance field.
   */

   public double getBalance()
   {
      return balance;
   }

}

and here is my TestAccount that i run from:

package assignment06;

import java.util.Scanner;         // Needed for Scanner class.
import java.text.DecimalFormat;  // Needed for DecimalFormat class.

/**
 *
 * @author Dsylvester
 */
public class testAccount {
 public static void main(String[] args)
    {
     String input;      // To hold user input
     double balance= 0 , interestRate=0;
     double interest = 0 ,deposit,withdrawl;
     double totalInterest = 0, totalDeposit = 0, totalWithdrawls = 0;
     
     int month=0;
     char repeat = 'Y';
     
     // Create Decimal Format.
     DecimalFormat dollar = new DecimalFormat ("#,###.00");
     
     
     // Create a Scanner object.
     Scanner keyboard = new Scanner(System.in);
     
     //Prompt for starting Balance.
     System.out.print(" What is your starting balance? ");
     balance = keyboard.nextDouble();
     
     // Prompt for Annual Interest Rate.
     System.out.print("What is your annual Interest Rate? ");
     interestRate = keyboard.nextDouble();
     
     // Create Savings Account Object.
     SavingsAccount account = new SavingsAccount(balance, interestRate);
     
     // Loop while user wants to continue.
     while (repeat == 'Y' ||  repeat == 'y')
     {
         month++;
         // Prompt for the amount of the deposit
         System.out.print("What is the amount of your deposit? ");
         deposit = keyboard.nextDouble();
        
         // Add deposits to total deposits.
         
         totalDeposit += deposit;
         
         // Add deposit to account balance.
        
         account.deposit(deposit);
     
         // Check for withdrawl from the account
         
         System.out.println("How much did you withdraw this month? ");
         withdrawl = keyboard.nextDouble();
        
         // Add withdrawl to total withdrawls.
         
         totalWithdrawls += withdrawl;
         
         // Subtract withdrawl from account balance.
         
         account.withdraw(withdrawl);

         // Calculate interest.
          account.calculateInterest(interest);

         // Add interest to total interest.
         
         totalInterest += interest;
         
         //Add interest to account balance.
         
         balance += interest;
         
        
 //Display the total deposits, total withdrawls, total interes and total balance
         
 System.out.println("Your total deposit is " + totalDeposit);
 System.out.println("Your total withdrawls were " + totalWithdrawls);
 System.out.println("Your total interest is " + totalInterest);
         
           
        

 System.out.println("Your total balance is $ " +
                 dollar.format(account.getBalance()));
                
         
         // Prompt user to continue.
         System.out.println("Calculate the month " + (month+1) + " (Y/N) ");
         repeat = keyboard.next().charAt(0);
        
   }
        System.exit(0);
 


}

}

[dannygirl sylvest]

somebody?

[Christophe Verré]

Please BePatient. And welcome to the ranch !

Did you try to debug it ? Debugging step by step would surely tell you where the problem is.
Using a few System.out.println here and there would also help you spot where the problem comes from.

[dannygirl sylvest]

the problem i'm having may be user error since it has to do more with how the interest was calculated. I just can't seem to find a way to fix it. I've been at this for 3 days trying to fix it, but keep it how my teacher wanted it to be. Maybe i'm using a constructor wrong?

[Christophe Verré]

Can you give an example of a user input, and the values that you are expecting ?

[Christophe Verré]

account.calculateInterest(interest);

interest is 0.0, and will always be. Also, you are not using the returned value of calculateInterest.

[Bobby Smallman]

Looks like you forgot to actually change the interest..... looks to me that from like 69 onwards you are dealing with your default interest of 0...

Without digging into it too much, I think you meant to first calculate the monthly interest rate, THEN give that rate to your line 69 to get the amount of interest earned....then take that and add it to your balance etc.

[Bobby Smallman]

Also, not that it is causing your errors, but since you are turning this in for a project, go back through and take a look at your variable names etc. Couple oddly named ones, some are capitalized, some are missing CamelCasing etc, might as well get it right if you are getting graded :-)

[dannygirl sylvest]

ok I'm getting this:

run:
 What is your starting balance? 1000
What is your annual Interest Rate? .10
What is the amount of your deposit? 0
How much did you withdraw this month? 
0
Your total deposit is 0.0
Your total withdrawls were 0.0
Your total interest is 0.010000000000000002
Your total balance is $ 1,000.00
Calculate the month 2 (Y/N) 

But i'm suppose to be getting this:
run:

What is your starting balance? 1000
What is your annual Interest Rate? .10
What is the amount of your deposit? 0
How much did you withdraw this month? 
0
Your total deposit is 0.0
Your total withdrawls were 0.0
Your total interest is 8.333333333
Your total balance is $ 1,008.33
Calculate the month 2 (Y/N) 

The monthly interest rate is the annual interest rate divided by 12. To add the monthly interest to the balance, multiply the monthly interest rate by the balance, and add the result to the balance.

[Bobby Smallman]

Yup, looks to be exactly what Christophe and I were pointing out. Look at your lines 69 - 77 in your main().

[dannygirl sylvest]

ok i see what you guys are saying. So i guess i'm having trouble getting the interest rate the correct value? should i say :

// Calculate interest from balance.
Balance *= ( and this is where i get a little confused) can you multiply a class method here? Or do i have to well darn i'm confused lol. I know what needs to be done but i can't figure out how to go about doing it no matter how much i stare at that darn textbook!

[Bobby Smallman]

It looks like you have the method in place to calculate the monthly interest rate, but you simply aren't using it. You also have a method for calculating the actual interest gained in the month, but you are passing it firstly your "interest" variable instead of your newly calculated monthly interest rate. So you need a variable for monthlyInterestRate which you will calculate by dividing your inputed annual interest rate (however you like, you can use your method you already made) and then when you go to call your calculateInterest, call it like

  interest = account.calculateInterest(monthlyInterestRate);   

In your original code you were never actually modifying your "interest" variable, and you never fully calculated your monthlyInterestRate.

Seems like you may have simply gotten confused about what your variables were because you have the functional parts there....your "interest" is really more like "interestEarned" if I am understanding it correctly.

[dannygirl sylvest]

I was trying to call the method MonthlyInterestRate(interestRate); but for some reason my teacher made it private instead of public so it brings up an error. I don't understand why he did that but i think i'm going to switch it to private and see how that goes.

Ok I did this :

public double MonthlyInterestRate( double annualrate)
{
return annualrate / 12 ;

}

and then this:

// Calculate interest from balance.
interest = balance *= account.MonthlyInterestRate(interestRate);


It gave me the correct interest. But now it didn't add it to my total balance. I'ts still 1, 000. What would cause that when it was working great a minute ago?

[Bobby Smallman]

You add your "interest" to the balance on your TestAccount class, but never modify the one in your SavingsAccount class which you use to call your balance total with line 89/90.

[dannygirl sylvest]

that's why im confused because i added it and still no correct total. I did this:

/

/ Add interest to total interest.
         
         totalInterest += interest;
         
       //Add interest to account balance.
         
           balance += interest;
         

[Bobby Smallman]

Like I said above, that "balance" there which you are adding it to is not your "account.balance" it is referring to your balance variable in your TestAccount class. Use your "account.setBalance()" method.

[dannygirl sylvest]

that didn't work either

[Bobby Smallman]

Post your updated code, and current input/output.