package computemortgage;
import javax.swing.JOptionPane;
import java.text.DecimalFormat;
// The following program gives the previous computeMortgage program a front-end
// GUI interface. I wrote the functions from bottom to top because I wasn't
// sure if they needed to be defined before they are used (as is necessary
// in C++.) Also, what about scope identifiers? (e.g. functions which are
// members of a class are usually defined outside of the class declaration
// in C++.)
public class ComputeMortgage
{
// pre: string asking for a value is passed in
// post: displays msgbox asking user for double and returns what user enters
static double getDouble(String askFor)
{ return Double.parseDouble(JOptionPane.showInputDialog(null, askFor)); }
// pre: string asking for a value is passed in
// post: displays msgbox asking user for integer and returns what user enters
static int getInt(String askFor)
{ return Integer.parseInt(JOptionPane.showInputDialog(null, askFor)); }
// pre: interest rate, number of years for loan, and loan amount passed in
// post: returns monthly loan payment
// used as helper function for void ShowPayment(double, int, double)
static double monthlyPayment(double rate, int years, double amount)
{ return amount*rate/(1 - (Math.pow(1/(1 + rate), years*12))); }
// pre: monthly loan payment and number of years for loan passed in
// post: returns total payment after loan + interest is payed off
// used as helper function for void totalPayment(double, int)
static double totalPayment(double monthly, int years)
{ return monthly*years*12; }
// pre: interest rate, number of years for loan, and loan amount passed in
// post: calculates and displays monthly and annual payment
static void showPayment(double annualRate, int numYears, double loanAmount)
{
double m = monthlyPayment(annualRate, numYears, loanAmount);
double a = totalPayment(m, numYears);
JOptionPane.showMessageDialog(null, "Monthly Payment = $" + m);
JOptionPane.showMessageDialog(null, "Total Payment = $" + a);
}
// pre: none
// post: computes how much $$$ is required to pay off a loan
public static void main(String[] args)
{
double annualRate = getDouble("Enter Annual Interest Rate")/100.0;
int numYears = getInt("Enter number of Years");
double loanAmount = getDouble("Enter loan Amount");
showPayment(annualRate, numYears, loanAmount);
}
}