![return -1.0; // return an error code
}
}
/** Get and validate the number of years from the text field */
public int getNumberOfYearsFromText() {
int years = 0;
boolean yearsValid;
try {
years = Integer.parseInt(tfNumberOfYears.getText());
yearsValid = (years >= 0);
}
catch (NumberFormatException ex) {
yearsValid = false;
}
if (yearsValid)
return years;
else { // set error indicators
tfNumberOfYears.setStyle("-fx-text-fill: red");
// Set tooltip to display when the mouse is hovered over the
// text box
Tooltip.install(tfNumberOfYears, ttNumberOfYears);
// At least display a red cursor when the field is blank
// Display red text without the blue highlighting when it isn't
if (tfNumberOfYears.getText().equals(""))
tfNumberOfYears.requestFocus();
return -1; // return an error code
}
}
/** Return monthly payment */
public double calculateMonthlyPayment(double interestRate,
double loanAmount, int numberOfYears) {
double monthlyInterestRate = interestRate / 1200;
return loanAmount * monthlyInterestRate / (1 - 1 /
Math.pow(1 + monthlyInterestRate, numberOfYears * 12));
}
/** Return total payment */
public double calculateTotalPayment(double interestRate,
double loanAmount, int numberOfYears) {
return calculateMonthlyPayment(interestRate, loanAmount, numberOfYears) *
numberOfYears * 12;
}
/** Round a money amount to the nearest cent */
// By creating this method and using it the way I did, I got the numbers
// to match the example in the book
public double round(double amount) {
return (int)(amount * 100) / 100.0;
}
public static void main(String[] args) {
launch(args);
}
}](https://image.slidesharecdn.com/74841209-fb21-484b-8198-349c827b880d-150804043313-lva1-app6891/85/CalculateLoanPayments-3-320.jpg)
CalculateLoanPayments
- 1. /* * This program is a loan payment calculator. It accepts a loan amount and * number of years in text boxes from the user, then displays a table showing * monthly payments and total payments for various interest rates, from 5% to 8% * in increments of 0.125%, when a button is clicked. This allows the user to * compare the effects of the various interest rates on the loan amount and * period. * * Author: Bill Rutherford * */ import javafx.application.Application; import javafx.geometry.*; import javafx.stage.Stage; import javafx.scene.Scene; import javafx.scene.control.*; import javafx.scene.layout.*; import javafx.scene.text.Font; public class CalculateLoanPayments extends Application { private TextField tfLoanAmount = new TextField(); private TextField tfNumberOfYears = new TextField(); private TextArea taPaymentTable = new TextArea(); private Tooltip ttLoanAmount = new Tooltip( "Loan amount must be a nonnegative money amount"); private Tooltip ttNumberOfYears = new Tooltip( "Number of years must be a nonnegative integer"); @Override public void start(Stage primaryStage) { final int SCENE_WIDTH = 555; final int SCENE_HEIGHT = 250; Button btShowTable = new Button("Show Table"); // Set text field properties tfLoanAmount.setPrefColumnCount(10); tfNumberOfYears.setPrefColumnCount(3); // Create a pane for text fields and button HBox inputPane = new HBox(10); inputPane.setPadding(new Insets(10, 10, 10, 10)); inputPane.setAlignment(Pos.CENTER_LEFT); inputPane.getChildren().addAll(new Label("Loan Amount "), tfLoanAmount, new Label("tNumber of Years "), tfNumberOfYears, btShowTable); // Set the button off to the right HBox.setMargin(btShowTable, new Insets(0, 0, 0, SCENE_WIDTH - 505)); // Set text area properties // Switch to a monospaced font; it's easier to get the columns to // line up with it taPaymentTable.setFont(Font.font("Lucida Console", 14)); taPaymentTable.setPrefRowCount(27); taPaymentTable.setPrefColumnCount(60); taPaymentTable.setEditable(false); // Create a pane to hold the controls and text area BorderPane mainPane = new BorderPane(); mainPane.setTop(inputPane); mainPane.setCenter(new ScrollPane(taPaymentTable)); // Set event handlers btShowTable.setOnAction(e -> showTable()); tfLoanAmount.setOnKeyTyped(e -> { // Restore normal text color tfLoanAmount.setStyle("-fx-text-fill: black");
- 2. // Turn off tooltip display Tooltip.uninstall(tfLoanAmount, ttLoanAmount); }); tfNumberOfYears.setOnKeyTyped(e -> { tfNumberOfYears.setStyle("-fx-text-fill: black"); Tooltip.uninstall(tfNumberOfYears, ttNumberOfYears); }); // Create a scene and place it in the stage Scene scene = new Scene(mainPane, SCENE_WIDTH, SCENE_HEIGHT); primaryStage.setTitle("Exercise 16_13"); primaryStage.setScene(scene); primaryStage.show(); } /** Create and display payment table */ public void showTable() { int numberOfYears = getNumberOfYearsFromText(); double loanAmount = getLoanAmountFromText(); if (loanAmount >= 0.0 && numberOfYears >= 0) { // input is valid // Declare table and create table header StringBuilder table = new StringBuilder( "Interest Ratet Monthly PaymenttTotal Payment"); // Create table body for (Double interestRate = 5.0; interestRate <= 8.0; interestRate += 0.125) { String line = String.format("n%-5stt %-21.2f%-20.2f", interestRate.toString(), round(calculateMonthlyPayment(interestRate, loanAmount, numberOfYears)), round(calculateTotalPayment(interestRate, loanAmount, numberOfYears))); table.append(line); } // Display table taPaymentTable.setText(table.toString()); } // else do nothing; wait for the user to correct the errors } /** Get and validate the loan amount from the text field */ public double getLoanAmountFromText() { double amount = 0.0; boolean amountValid; try { amount = Double.parseDouble(tfLoanAmount.getText()); amountValid = (amount >= 0.0); } catch (NumberFormatException ex) { amountValid = false; } if (amountValid) return amount; else { // set error indicators tfLoanAmount.setStyle("-fx-text-fill: red"); // Set tooltip to display when the mouse is hovered over the // text box Tooltip.install(tfLoanAmount, ttLoanAmount); // At least display a red cursor when the field is blank // Display red text without the blue highlighting when it isn't if (tfLoanAmount.getText().equals("")) tfLoanAmount.requestFocus();
- 3. return -1.0; // return an error code } } /** Get and validate the number of years from the text field */ public int getNumberOfYearsFromText() { int years = 0; boolean yearsValid; try { years = Integer.parseInt(tfNumberOfYears.getText()); yearsValid = (years >= 0); } catch (NumberFormatException ex) { yearsValid = false; } if (yearsValid) return years; else { // set error indicators tfNumberOfYears.setStyle("-fx-text-fill: red"); // Set tooltip to display when the mouse is hovered over the // text box Tooltip.install(tfNumberOfYears, ttNumberOfYears); // At least display a red cursor when the field is blank // Display red text without the blue highlighting when it isn't if (tfNumberOfYears.getText().equals("")) tfNumberOfYears.requestFocus(); return -1; // return an error code } } /** Return monthly payment */ public double calculateMonthlyPayment(double interestRate, double loanAmount, int numberOfYears) { double monthlyInterestRate = interestRate / 1200; return loanAmount * monthlyInterestRate / (1 - 1 / Math.pow(1 + monthlyInterestRate, numberOfYears * 12)); } /** Return total payment */ public double calculateTotalPayment(double interestRate, double loanAmount, int numberOfYears) { return calculateMonthlyPayment(interestRate, loanAmount, numberOfYears) * numberOfYears * 12; } /** Round a money amount to the nearest cent */ // By creating this method and using it the way I did, I got the numbers // to match the example in the book public double round(double amount) { return (int)(amount * 100) / 100.0; } public static void main(String[] args) { launch(args); } }