Creating a Mortgage Calculator in Java

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I added a new method, createJMenuBar(), in the mcFrame class to add the main menu bar with a menu called Available Mortgages. When a user clicks on one of the available mortgages, the year JTextField and the rate JTextField will be filled with the available choices. Then the user must enter the loan amount and click Calculate button to see the result. I tested the source code on Win 7 machine and it works ok. Let me know if you have any problems.

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;
import java.util.Scanner;
import javax.swing.*;

public class mortgageCalculatorGui2 {

public static void main(String[] args) {
//------------------------
//Use GUI to calculate mortgages
mcFrame mc = new mcFrame();
mc.createWindow();
}
}

class MortgageCalculator {

private int years; //number of years on the loan
private double loan; // amount of loan
private double interest;// percentage of interest
private double monthlyPayment;// amount ofmonthly payment
private double totalPayment; // this is the loan amount plus interest
private double interestPaid;//monthly interst payment
private double balanceLoan;// loan balance
private double balancePrinciple;// principle balance
//display variables
private String str;// header,
private int displayCount;//display counter
private int scroll;//scroll counter
private Scanner input;
//display for gui
private StringBuffer strForGui; //string buffer for gui display

public MortgageCalculator(int years, double loan, double interest) {
this.years = years;
this.loan = loan;
this.interest = interest;
input = new Scanner(System.in);
//get monthly payment
//interest is in percentage, so for monthly interest, interest = (interset/100)/12=interest/1200..
monthlyPayment = loan * (interest / 1200) * (1 + 1 / (Math.pow(1 + interest / 1200, years * 12) - 1));
totalPayment = monthlyPayment * years * 12;//the total payment is the sum of loan amount and the
//total of the interest paid over the course of the loan
balanceLoan = totalPayment;
balancePrinciple = this.loan;
}
//use to display schedule on console

public void displaySchedule() {
//display schedule
while (displayCount < years * 12) {
//prepare the heading
str = (String.format("%10s %10s %10s %10s", "month", "payment", "interest", "balance"));// returns the next element in the literation, 10s means reserve 10 ...