LoanCalculator.java

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.geometry.HPos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

public class LoanCalculator extends Application {
  private TextField tfAnnualInterestRate = new TextField();
  private TextField tfNumberOfYears = new TextField();
  private TextField tfLoanAmount = new TextField();
  private TextField tfMonthlyPayment = new TextField();
  private TextField tfTotalPayment = new TextField();
  private Button btCalculate = new Button("Calculate");
  
  @Override // Override the start method in the Application class
  public void start(Stage primaryStage) {
    // Create UI
    GridPane gridPane = new GridPane();
    gridPane.setHgap(5);
    gridPane.setVgap(5);
    gridPane.add(new Label("Annual Interest Rate:"), 0, 0);
    gridPane.add(tfAnnualInterestRate, 1, 0);
    gridPane.add(new Label("Number of Years:"), 0, 1);
    gridPane.add(tfNumberOfYears, 1, 1);
    gridPane.add(new Label("Loan Amount:"), 0, 2);
    gridPane.add(tfLoanAmount, 1, 2);
    gridPane.add(new Label("Monthly Payment:"), 0, 3);
    gridPane.add(tfMonthlyPayment, 1, 3);
    gridPane.add(new Label("Total Payment:"), 0, 4);
    gridPane.add(tfTotalPayment, 1, 4);
    gridPane.add(btCalculate, 1, 5);

    // Set properties for UI
    gridPane.setAlignment(Pos.CENTER);
    tfAnnualInterestRate.setAlignment(Pos.BOTTOM_RIGHT);
    tfNumberOfYears.setAlignment(Pos.BOTTOM_RIGHT);
    tfLoanAmount.setAlignment(Pos.BOTTOM_RIGHT);
    tfMonthlyPayment.setAlignment(Pos.BOTTOM_RIGHT);
    tfTotalPayment.setAlignment(Pos.BOTTOM_RIGHT);
    tfMonthlyPayment.setEditable(false);
    tfTotalPayment.setEditable(false);
    GridPane.setHalignment(btCalculate, HPos.RIGHT);

    // Process events
    btCalculate.setOnAction(e -> calculateLoanPayment());

    // Create a scene and place it in the stage
    Scene scene = new Scene(gridPane, 400, 250);
    primaryStage.setTitle("LoanCalculator"); // Set title
    primaryStage.setScene(scene); // Place the scene in the stage
    primaryStage.show(); // Display the stage
  }
  
  private void calculateLoanPayment() {
    // Get values from text fields
    double interest =
      Double.parseDouble(tfAnnualInterestRate.getText());
    int year = Integer.parseInt(tfNumberOfYears.getText());
    double loanAmount =
      Double.parseDouble(tfLoanAmount.getText());

    // Create a loan object. Loan defined in Listing 10.2
    Loan loan = new Loan(interest, year, loanAmount);

    // Display monthly payment and total payment
    tfMonthlyPayment.setText(String.format("$%.2f",
      loan.getMonthlyPayment()));
    tfTotalPayment.setText(String.format("$%.2f",
      loan.getTotalPayment()));
  }
  
  /**
   * The main method is only needed for the IDE with limited
   * JavaFX support. Not needed for running from the command line.
   */
  public static void main(String[] args) {
    launch(args);
  }
}