//================== Click event in frmMain ================


    private void btnCalcActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
        double irate;
        double start;
        double end;
        double years;
        double amount;
        double balance;
        String buff;
        
        try
        {
            irate = Double.parseDouble(txtInterestRate.getText());
            start = Double.parseDouble(txtStartAmount.getText());
            years = Double.parseDouble(txtYearsToWithdraw.getText());
            amount = Double.parseDouble(txtAmountToWithdraw.getText());
            
            ClsAnnuity myAnnuity = new ClsAnnuity(irate, years, start, amount);
            
            balance = myAnnuity.getEndingBalance();
            buff = String.format("$%.2f", balance);
            
            txtEndingBalance.setText(buff);
            txtYearsFundLasts.setText(Double.toString(myAnnuity.getYears()));    
        } catch (Exception ex)
        {
            System.out.println(ex.getMessage());
        }

    }                                       
  

//================= ClsAnnuity ===================================================

public class ClsAnnuity {
    //============================== Instance Members ===================
    private double interestRate;
    private double yearsToWithdraw;
    private double startingBalance;
    private double endingBalance;
    private double annualWithdrawal;
   
    //============================== Constructor ========================
    
    public ClsAnnuity(double i, double ytw, double sb, double aw)
    {
        if (i > 1.0)
            i *= .01;
        interestRate = i;
        if (ytw > 0.0)
            yearsToWithdraw = ytw;
        if (sb > 0.0)
            startingBalance = sb;
        if(aw > 0.0)
            annualWithdrawal = aw;
    }
    //============================== Property methods ====================
    public double getYears()
    {
        return yearsToWithdraw;
    }
    //============================== General Methods =====================
    
    public double getEndingBalance()
    {
        int i;
        double interest;
        double bal = startingBalance;
        double end;
        
        for (i = 0; i < (int) yearsToWithdraw; i++)
        {
            interest = interestRate * bal;
            bal = interest + bal;
            bal -= annualWithdrawal;
            if (bal < 0)
                break;
        }
        yearsToWithdraw = i;
        return bal;
    }
   
}