Amortization.java

import javax.swing.*;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.text.NumberFormat;
import java.util.Locale;

public class Amortization {

    private double interestRate, loanBalance;
    private int loanYears;

    private static NumberFormat nf =
            NumberFormat.getCurrencyInstance(new Locale("en", "US"));

    public Amortization(double loanBalance, double interestRate, int loanYears) {
        this.loanBalance = loanBalance;
        this.interestRate = interestRate;
        this.loanYears = loanYears;
        // DO NOT CALL CALCPAYMENT HERE!!!!!!!
    }

    private double getMonthlyPayment() {
        double loanBalance = 20000;
        double calcRate = (7.5/100) / 12;
        int calcYears = 5 * 12;

        double numerator = calcRate * Math.pow((1+calcRate), calcYears);
        double denominator = Math.pow((1+calcRate),calcYears) - 1;
        return loanBalance * (numerator/denominator);
    }

    public int getNumberOfPayments() {
        return 12 * loanYears;
    }

    private void saveReport(String filename) throws IOException {
        double payment = this.getMonthlyPayment();
        double monthlyInterest, principal;
        FileWriter writer = new FileWriter("Amoritization.txt");
        PrintWriter report = new PrintWriter(writer);

        report.println("Monthy Payment: $" + nf.format(payment));
        report.println("Month\tInterest\tPrincipal\tBalance");
        report.println("-------------------------------------------------");
        for (int month = 1; month <= getNumberOfPayments(); month++) {
            monthlyInterest = interestRate / 12.0 * loanBalance;

            if (month != getNumberOfPayments()) {
                principal = payment - monthlyInterest;
            } else {
                principal = loanBalance;
                payment = loanBalance + monthlyInterest;
            }
            loanBalance -= principal;

            report.println(month + "\t" + nf.format(monthlyInterest) + "\t\t"
                    + nf.format(principal) + "\t\t" + nf.format(loanBalance));
        }
        report.close();
    }

    public double getLoanBalance() {
        return loanBalance;
    }

    public double getInterestRate() {
        return interestRate;
    }

    public int getLoanYears() {
        return loanYears;
    }

    @Override
    public String toString() {
        return "Loan Amount: " + nf.format(loanBalance) +
                "\nInterest Rate: " + interestRate +
                "\nLoan Years: " + loanYears +
                "\nMonthly Payments: " + nf.format(getMonthlyPayment());
    }

    public static void main(String[] args) {

        double loanAmount = Double.parseDouble(JOptionPane.showInputDialog("Enter the amount of " +
                "the Loan:"));
        double interestRate = Double.parseDouble(JOptionPane.showInputDialog("Enter the annual " +
                "interest rate of the loan:"));
        int loanYears = Integer.parseInt(JOptionPane.showInputDialog("Enter the length of the " +
                "loan, in years:"));
        Amortization a = new Amortization(loanAmount, interestRate, loanYears);
        JOptionPane.showMessageDialog(null,a,"Your Results",1);

    }

}