Project: Mortgage Calculator

Given input principal \(P\), annual interest rate \(R\), years \(Y\), the monthly mortgage is:

\[ P\frac{r(1+ r)^{n}}{(1+ r)^{n} - 1} \]

where \(r=\frac{R}{12}\) is the monthly interest rate, \(n=12Y\) is the total months.

Solution:

import java.text.NumberFormat;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final byte MONTHS_IN_YEAR = 12;
        final byte PERCENT = 100;

        Scanner scanner = new Scanner(System.in);
        System.out.print("Principal: ");
        int principal = scanner.nextInt();
        System.out.print("Annual Interest Rate: ");
        float annualInterestRate = scanner.nextFloat();
        System.out.print("Period (Years): ");
        byte years = scanner.nextByte();

        float monthlyInterestRate = (annualInterestRate / PERCENT) / MONTHS_IN_YEAR;
        int months = years * MONTHS_IN_YEAR;

        double mortgage = principal * (monthlyInterestRate *
                Math.pow(1 + monthlyInterestRate, months) /
                (Math.pow(1 + monthlyInterestRate, months) - 1));
        System.out.println("Mortgage: " + 
                NumberFormat.getCurrencyInstance().format(mortgage).trim());
    }
}