Loan calculator using tableview in JavaFX - javafx

Question

I am attempting to make a loan calculator that shows payment number, interest, principal, and balance in tableview in JavaFX. Right now only the principal and balance columns are populating. I am fairly new to JavaFX, so I am not sure if I have made a mistake in FX or in my formula. Here is my code:
public class LoanTable extends Application {
Integer payment;
Double interest;
Double principal;
Double balance;
#Override
public void start(Stage primaryStage) {
BorderPane border = new BorderPane();
GridPane grid = new GridPane();
ScrollPane scroll = new ScrollPane();
Label labelTitle = new Label("Enter Loan Amount, Number of Years, and Annual Interest Rate");
labelTitle.getStyleClass().add("labelTitle");
Label loan = new Label("Loan Amount");
TextField loanAmount = new TextField();
Label years = new Label("Number of Years");
TextField numYears = new TextField();
Label interestRate = new Label("Annual Interest Rate");
TextField rate = new TextField();
Button compute = new Button("Display Loan Schedule");
TableView<Finance> table = new TableView<>();
TableColumn paymentColumn = new TableColumn("Payment#");
paymentColumn.setMinWidth(200);
paymentColumn.setCellValueFactory(new PropertyValueFactory<Finance, Integer>("payment"));
TableColumn interestColumn = new TableColumn("Interest");
interestColumn.setMinWidth(200);
interestColumn.setCellValueFactory(new PropertyValueFactory<Finance, Double>("interest"));
TableColumn prinColumn = new TableColumn("Principal");
prinColumn.setMinWidth(200);
prinColumn.setCellValueFactory(new PropertyValueFactory<Finance, Double>("principal"));
TableColumn balColumn = new TableColumn("Balance");
balColumn.setMinWidth(200);
balColumn.setCellValueFactory(new PropertyValueFactory<Finance, Double>("balance"));
table.getColumns().addAll(paymentColumn, interestColumn, prinColumn, balColumn);
grid.add(labelTitle, 0, 0);
grid.add(new Label(), 0, 1);
grid.add(loan, 0, 2);
grid.add(loanAmount, 1, 2);
grid.add(years, 0, 3);
grid.add(numYears, 1, 3);
grid.add(interestRate, 0, 4);
grid.add(rate, 1, 4);
grid.add(compute, 4, 0);
scroll.setContent(table);
border.setTop(grid);
border.setBottom(scroll);
Scene scene = new Scene(border, 800, 800);
scene.getStylesheets().add("loan_table.css");
primaryStage.setScene(scene);
primaryStage.show();
compute.setOnAction((e) -> {
Double loanTotal = Double.parseDouble(loanAmount.getText());
Integer year = Integer.parseInt(numYears.getText());
Double rateInterest = Double.parseDouble(rate.getText());
double monthlyInterest = rateInterest / 1200;
double monthlyPayment = loanTotal * monthlyInterest / (1 - 1 / Math.pow(1 + monthlyInterest, year * 12));
balance = loanTotal;
for(int i = 1; i < year * 12; i++) {
interest = monthlyInterest * balance;
principal = monthlyPayment - interest;
balance = balance - principal;
payment = i + 1;
}
ObservableList<Finance> data = FXCollections.observableArrayList(new Finance(payment, interest, principal, balance));
table.setItems(data);
});
}
public static class Finance {
private final SimpleIntegerProperty payment;
private final SimpleDoubleProperty interest;
private final SimpleDoubleProperty principal;
private final SimpleDoubleProperty balance;
private Finance(int payment, double interest, double principal, double balance) {
this.payment = new SimpleIntegerProperty(payment);
this.interest = new SimpleDoubleProperty(interest);
this.principal = new SimpleDoubleProperty(principal);
this.balance = new SimpleDoubleProperty(balance);
}
public Integer getPayment(int numYears) {
return payment.get();
}
public Double getInterest(double rate) {
return interest.get();
}
public Double getPrincipal() {
return principal.get();
}
public Double getBalance() {
return balance.get();
}
}
public static void main(String[] args) {
launch(args);
}
}