halfAssedDriver.java

import javax.swing.JOptionPane;

public class DriverMortgageClass {

    private Mortgage mortgage;

    public void start() {
        double yearlyInterestRate = 0;
        int numberOfYears = 0;
        double loanAmount = 0;

        yearlyInterestRate = Double.parseDouble(JOptionPane.showInputDialog("Enter yearly interest rate, for example 8.50:")) / 100;
        numberOfYears = Integer.parseInt(JOptionPane.showInputDialog("Enter number of years as an integer, for example 5:"));
        loanAmount = Double.parseDouble(JOptionPane.showInputDialog("Enter loan amount, for example 10000.00:"));

        mortgage = new Mortgage(yearlyInterestRate, numberOfYears, loanAmount);

        JOptionPane.showMessageDialog(null, "Monthly payment is " + String.format("%.2f", mortgage.monthlyPayment())
                + "\nThe total payment is " + String.format("%.2f", mortgage.totalPayment()));
    }

    /**
     * Main method
     */
    public static void main(String[] args) {
        DriverMortgageClass driver = new DriverMortgageClass();
        driver.start();
    }
}

HereGarrett.java

public class Mortgage {

    private double annualInterestRate;
    private int numberOfYears;
    private double loanAmount;

    public Morgage() {
        this(0.085, 10, 10000);
    }

    public Morgage(double annualInterestRate, int numberOfYears, double loanAmount) {
        this.annualInterestRate = annualInterestRate;
        this.numberOfYears = numberOfYears;
        this.loanAmount = loanAmount;
    }

    public double getAnnualInterestRate() {
        return annualInterestRate;
    }

    public void setAnnualInterestRate(double annualInterestRate) {
        this.annualInterestRate = annualInterestRate;
    }

    public int getNumberOfYears() {
        return numberOfYears;
    }

    public void setNumberOfYears(int numberOfYears) {
        this.numberOfYears = numberOfYears;
    }

    public double getLoanAmount() {
        return loanAmount;
    }

    public void setLoanAmount(double loanAmount) {
        this.loanAmount = loanAmount;
    }

    public double monthlyPayment() {
        double monthlyInterestRate = annualInterestRate / 12;
        return loanAmount * (monthlyInterestRate / (1 - Math.pow(1 + monthlyInterestRate, -numberOfYears * 12)));
    }

    public double totalPayment() {
        return monthlyPayment() * numberOfYears * 12;
    }
}