AmortizationCalculator.java

import java.util.Scanner;
import java.io.FileWriter;
import java.io.IOException;
import java.io.BufferedWriter;

public class AmortizationCalculator {
  private static Scanner scanner = new Scanner(System.in);
  private static double monthlyRate;

  public static void main(String[] args){
    System.out.println("Please enter your total loan amount: ");
    double principal = scanner.nextDouble();
    System.out.println("Please enter your APR interest rate (format is 00.00):");
    double interest = scanner.nextDouble();
    System.out.println("Please enter your total amount of payments: ");
    int numberOfPayments = scanner.nextInt();

    monthlyRate = (double) interest / 1200;
    double amortization = calculate(principal, numberOfPayments);
    System.out.println("=====================================================");
    System.out.printf("Your periodic payment amount is %.4f\n", amortization);
    System.out.println("=====================================================");

    printTable(principal, numberOfPayments);
  }

  private static double calculate(double principal, int numberOfPayments){
    double amortization = 0.00;

    if (monthlyRate > 0) {
      amortization = (principal * monthlyRate * Math.pow(1 + monthlyRate, (double)numberOfPayments)) /
                (Math.pow(1 + monthlyRate, (double)numberOfPayments) - 1);
    } else {
      amortization = principal / numberOfPayments;
    }
    return amortization;
  }

  private static void printTable(double principal, int numberOfPayments){
    // Begin printing table
    Object[] headers = {"Payment #", "Amount Due", "Interest Due", "Principal Due", "Amount Left"};
    System.out.println("\n=================Your Mortgage Payoff Table============================");
    System.out.println("\n=================--------------------------============================");
    System.out.format("%5s %12s %18s %16s \n", headers);
    System.out.println("\n=======================================================================");

    //Establish values to display
    double monthlyPayment = calculate(principal, numberOfPayments);
    double interestPayment = 0.0;
    double principalDue = 0.0;
    double principalLeft = principal;
    boolean loanPaid = false;

    Object[][] rows = new Object[numberOfPayments][];
    for(int i = 0; i < numberOfPayments; i++) {
      interestPayment = monthlyRate * principalLeft;
      principalDue = monthlyPayment - interestPayment;
      principalLeft = Math.abs(principalLeft - principalDue);
      Object[] row = {i+1, monthlyPayment, interestPayment, principalDue, principalLeft};
      rows[i] = row;
      System.out.format("%5d%17.4f%19.4f%19.4f%17.4f\n", row);
    }

    promptToSaveCSV(rows);
  }

  private static void promptToSaveCSV(Object[][] rows){
    System.out.println("Would you like to save the results to a CSV file? [Yes/No]:");
    String response = scanner.next();

    if ("yes".equalsIgnoreCase(response)) {
      try{
        FileWriter fileWriter = new FileWriter("amortization_table.csv");
        BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
        StringBuilder stringBuilder = new StringBuilder();

        for(Object[] row: rows){
          for(Object column: row){
            if (stringBuilder.length() != 0){
              stringBuilder.append(',');
            }
            stringBuilder.append(column);
          }
          stringBuilder.append("\n");
          bufferedWriter.write(stringBuilder.toString());
          stringBuilder.setLength(0);
        }
        bufferedWriter.close();

        System.out.println("Results saved to amortization_table.csv");
      } catch(IOException e){
        e.printStackTrace();
      }
    } else {
      System.out.println("You chose not to save results in a CSV file.");
    }
  }
}