Question

A bank offers college loans that can be repaid in 5, 10, 15, 20, 25, or 30 years. Write an app that allows the user to enter the amount of the loan and the annual interest rate. Based on these values, the app should display the loan lengths in years and their corresponding monthly payments.  

Design the form window using javaFX as follows:

• Enter the Amount Of Loan and Interest Rate using TextField objects (remember that it will be necessary to convert the text String from the TextFields using a parse, method, e.g. Double.parseDouble()
• Enter the Number Of Years using six RadioButton objects
• Calculate the Monthly Payment displayed in a Label when a Button executes an event handler (since the app will only calculate the monthly payment for the currently selected RadioButton, it will not be necessary to also display the loan length in years as part of the output specified in the text)

Answer 1

Dear Student,

I have created sample javafx application for the scenario you have asked in the question:-

1. I have used three files to create this project and the comments are used in the file for your ready reference.

2. These files are (a) MonthlyPaymentCalculatorMain.java

(b) FXMLMonthlyPaymentCalculatorController

(c) FXMLMonthlyPaymentCalculator.fxml

3. Screenshot of MonthlyPaymentCalculatorMain.java which is mentioned below:-

4. Screenshot of FXMLMonthlyPaymentCalculatorController.java file is mentioned below:-

5. Screenshot of FXMLMonthlyPaymentCalculator.fxml file is mentioned below:-

6. MonthlyPaymentCalculatorMain.java file in textual format is mentioned below:-

package javafx.monthly.payment;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.stage.WindowEvent;

public class MonthlyPaymentCalculatorMain extends Application{

@FXML
private StackPane stackPane;

//Overriding start method of javafx Application class
public void start(Stage stage) throws Exception{

try{
   //Creating root class object with the given xml file placed in resource folder
Parent root = FXMLLoader.load(getClass().getResource("/FXMLMonthlyPaymentCalculator.fxml"));
Scene scene = new Scene(root);
stage.setScene(scene);
  
//Setting title
stage.setTitle("Java FX Demo Calculator");
  
//Showing stage
stage.show();
  
stage.setOnCloseRequest(new EventHandler<WindowEvent>() {
public void handle(WindowEvent arg0) {
Platform.exit();
}
});
}
catch (Exception e){
throw e;
}
}

//Main method
public static void main(String[] args){
try{
launch(args);
}
catch (Exception e){
e.printStackTrace();
}
}
}

7. FXMLMonthlyPaymentCacluatorController.java file in textual format is mentioned below:-

package javafx.monthly.payment;

import javafx.fxml.FXML;

import javafx.scene.control.TextField;

import javafx.scene.control.ToggleGroup;

import javafx.event.ActionEvent;

import javafx.scene.control.Label;
import javafx.scene.control.RadioButton;

public class FXMLMonthlyPaymentCalculatorController {
  
   //Declaring TextBox for loan amount
   @FXML
   private TextField txtLoanAmount;
  
   //Declaring TextBox for interest rate
   @FXML
   private TextField txtInterestRate;
  
   //Declaring togglegroup for loan tenure
   @FXML
   private ToggleGroup loanLengthOfYears;
  
   //Declaring label for showing final output
   @FXML
   private Label lblCalculatedMonthlyPayment;

   /*This method will be invoked only on clicking radio button and it will set the
   label with the calculated monthly payment*/
   @FXML
   public void calculateMonthlyPayment(ActionEvent event) {
      
       //Reading loan amount
       String strLoanAmount=txtLoanAmount.getText();
      
       //Reading loan interest rate
       String strInterestRate=txtInterestRate.getText();
      
       /*Perform action for calculating monthly payment only if loan amount and
       interest rate are not blank or not entered by user*/
       if(!strLoanAmount.isBlank() && !strInterestRate.isBlank()) {
          
           //convert loan amount to double using parse method
           double loanAmount=Double.parseDouble(strLoanAmount);
          
           /*convert interest rate to double using parse method and divide it
           by 12*100 to get interest per month*/
           double interestRate=Double.parseDouble(strInterestRate)/(12*100);
          
           //Get selected radio button of loan length
           RadioButton selectedLoanLengthInYears=(RadioButton) loanLengthOfYears.getSelectedToggle();
          
           //Read loan length
           String strLoanLength=selectedLoanLengthInYears.getText();
          
           ////Parse loan length to int and multiply it to 12 to get the no of months
           int loanLength=Integer.parseInt(strLoanLength)*12;
          
           //Calculate monthly payment using the below formula
           double monthlyPayment=(loanAmount*interestRate*Math.pow(1+interestRate,loanLength))/
                   (Math.pow(1+interestRate,loanLength)-1);
          
           //round off monthly payment to nearest integer
           long monthlyPaymentRoundOff=Math.round(monthlyPayment);
          
           //Display the monthly payment in label
           lblCalculatedMonthlyPayment.setText("Monthly payment is "+monthlyPaymentRoundOff);
          
       }
   }
}

8. FXMLMonthlyPaymentCalculator.fxml file in textual format is mentioned below:-

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.RadioButton?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.control.ToggleGroup?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity"
minWidth="-Infinity" prefHeight="561.0" prefWidth="778.0" xmlns="http://javafx.com/javafx/11.0.1"
xmlns:fx="http://javafx.com/fxml/1" fx:controller="javafx.monthly.payment.FXMLMonthlyPaymentCalculatorController">
<children>
<Label layoutX="212.0" layoutY="35.0" prefHeight="35.0" prefWidth="402.0" text="Loan Monthly Payment Calculator">
<font>
<Font name="System Bold" size="24.0" />
</font>
</Label>
<TextField fx:id="txtLoanAmount" layoutX="339.0" layoutY="103.0"/>
<TextField fx:id="txtInterestRate" layoutX="339.0" layoutY="148.0"/>
<Label layoutX="121.0" layoutY="105.0" prefHeight="20.0" prefWidth="168.0" text="Enter the Amount of loan">
<font>
<Font size="14.0" />
</font>
</Label>
<Label layoutX="121.0" layoutY="152.0" prefHeight="17.0" prefWidth="137.0" text="Interest Rate">
<font>
<Font size="14.0" />
</font>
</Label>
<RadioButton layoutX="339.0" layoutY="201.0" mnemonicParsing="false" onAction="#calculateMonthlyPayment" text="5">
<toggleGroup>
<ToggleGroup fx:id="loanLengthOfYears" />
</toggleGroup>
</RadioButton>
<RadioButton layoutX="375.0" layoutY="201.0" mnemonicParsing="false" onAction="#calculateMonthlyPayment" text="10"
toggleGroup="$loanLengthOfYears" />
<RadioButton layoutX="424.0" layoutY="201.0" mnemonicParsing="false" onAction="#calculateMonthlyPayment" text="15"
toggleGroup="$loanLengthOfYears" />
<RadioButton layoutX="471.0" layoutY="201.0" mnemonicParsing="false" onAction="#calculateMonthlyPayment" text="20"
toggleGroup="$loanLengthOfYears" />
<RadioButton layoutX="522.0" layoutY="202.0" mnemonicParsing="false" onAction="#calculateMonthlyPayment" text="25"
toggleGroup="$loanLengthOfYears" />
<RadioButton layoutX="566.0" layoutY="202.0" mnemonicParsing="false" onAction="#calculateMonthlyPayment" text="30"
toggleGroup="$loanLengthOfYears" />
<Label layoutX="121.0" layoutY="200.0" prefHeight="17.0" prefWidth="137.0" text="Enter no of years">
<font>
<Font size="14.0" />
</font>
</Label>
<Label fx:id="lblCalculatedMonthlyPayment" layoutX="221.0" layoutY="263.0" prefHeight="35.0" prefWidth="429.0" />
</children>
</AnchorPane>

9. Output of the above code is mentioned below:-

10. As most of the code is commented. Still you may require need to clear doubt to any of your queries inside the code. Then you may feel free to reach me through comments section, I will reply you as early as possible.

11. Inside controller I have used generalized formula to calculate the monthly payment, if you have different formula for calculating monthly payment you can just replace the logic inside the calculateMonthlyPayment method of controller class.

Thanks!!

Happy Learning!!