n this exercise, you$$ll update the JavaFX MPG application to handle invalid data. When you$$re done, the application should display a dialog box that looks like this when invalid data is entered:

Test the application with invalid data $1.$ Open the project named ch$12\_$ex$2\_$MPG in the ex$\_$starts directory. $2.$ Run the application and enter invalid data for miles or gallons. Then, click the Calculate button.

$3.$ Review the resulting error messages that are displayed in the console. Then, close the application by clicking the $$X$$ in the upper right corner.

Check user entries and display error messages in a dialog box $4.$ Add a validation class like the one shown in this chapter to the project. To keep things simple, add this class to the same package as the MpgApp class.

$5.$ Modify the code for the event handler method so it uses the validation class to check user entries.

$6.$ Add code that displays any messages about invalid entries in a dialog box. $7.$ Test the data validation by running the project and entering invalid data. When you$$re done testing, close the application.Exercise $12-2$ Add data validation

In this exercise, you'll update the JavaFX MPG application to handle invalid

data. When you're done, the application should display a dialog box that looks

like this when invalid data is entered:

Test the application with invalid data

Open the project named ch$12\_$ex$2\_$MPG in the ex$\_$starts directory.

Run the application and enter invalid data for miles or gallons. Then, click the

Calculate button.

Review the resulting error messages that are displayed in the console. Then,

close the application by clicking the $"x"$ in the upper right corner.

Check user entries and display error messages in a dialog box

Add a validation class like the one shown in this chapter to the project. To

keep things simple, add this class to the same package as the MpgApp class.

Modify the code for the event handler method so it uses the validation class to

check user entries.

Add code that displays any messages about invalid entries in a dialog box.

Test the data validation by running the project and entering invalid data. When

you're done testing, close the application.

My code:

import javafx.application.Application;

import javafx.event.ActionEvent;

import javafx.event.EventHandler;

import javafx.geometry.Insets;

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 MPGApplication extends Application $\{$

@Override

public void start$($Stage primaryStage$)\{$

Button btn $=$ new Button$()$;

TextField miles $=$ new TextField$()$;

TextField gallons $=$ new TextField$()$;

TextField mpg $=$ new TextField$()$;

mpg$.$setEditable$($false$)$;

btn$.$setText$("$Calculate$")$;

btn$.$setOnAction$($new EventHandler$()\{$

@Override

public void handle$($ActionEvent event$)\{$

try$\{$

double mil $=$ Double.parseDouble$($miles$.$getText$())$;

double gall $=$ Double.parseDouble$($gallons$.$getText$())$;

double mpgVal $=$ mil$/$gall;

mpg$.$setText$($mpgVal$+"")$;

$\}$catch$($Exception e$)\{$

System.out.println$("$Error$")$;

$\}$

$\}$

$\})$;

GridPane root $=$ new GridPane$()$;

root.setVgap$(10)$;

root.setHgap$(10)$;

root.setPadding$($new Insets$(25,25,25,25))$;

root.add$($new Label$("$Miles : $"),0,0)$;

root.add$($miles$,1,0)$;

root.add$($new Label$("$Gallons : $"),0,1)$;

root.add$($gallons$,1,1)$;

root.add$($new Label$("$MPG : $"),0,2)$;

root.add$($mpg$,1,2)$;

root.add$($btn$,1,3)$;

Scene scene $=$ new Scene$($root$,300,250)$;

primaryStage.setTitle$("$Miles Per Gallon Calculator"$)$;

primaryStage.setScene$($scene$)$;

primaryStage.show$()$;

$\}$

public static void main$($String$[]$ args$)\{$

launch$($args$)$;

$\}$

$\}$