This is javafx code. It is run but I want to add message. when i don\'t put noth

Question

 This is javafx code. It is run but I want to add message. when i don't put nothing. And when i click calculate button without put in number, it's not working.  package Homework;  import javafx.application.Application; import javafx.geometry.Pos; import javafx.scene.Scene; import javafx.scene.control.*; import javafx.scene.control.Button; import javafx.scene.control.Label; import javafx.scene.control.TextField; import javafx.scene.layout.*; import javafx.scene.text.Font; import javafx.scene.text.FontWeight; import javafx.stage.Stage; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.geometry.Insets; import javafx.scene.control.RadioButton; import javafx.stage.Stage; import javafx.scene.layout.GridPane; import java.awt.Checkbox; import javafx.scene.control.CheckBox; import org.w3c.dom.events.Event; import javafx.application.Platform;  import java.text.DecimalFormat;     public class Reimbursement extends Application implements EventHandler<ActionEvent> {     //Array with coffee name     private String[] coffeeNames = {"Regular", "Espresso", "Latte", "Frappucino", "Mocha"};     Stage window;     Scene scene;     Button btn;     Button resetButton;     TextField textDays;     TextField textAirFare;     TextField textCarRental;     TextField textMilesDriven;     TextField textParkingFees;     TextField textTaxiCharges;     TextField textRegisFees;     TextField textLodgingCharges;     TextField textSelection;     ComboBox<String> comboBox;     CheckBox correctCheckBox;     RadioButton button1;       @Override     public void start(Stage primaryStage) throws Exception {         window = primaryStage;         window.setTitle("Reimbursement Calculator");         Font font = Font.font("Arial", FontWeight.BOLD, 12);            //GridPane with 10 px padding around edge         GridPane grid = new GridPane();         grid.setAlignment(Pos.CENTER);         grid.setPadding(new Insets(20));         grid.setHgap(20);         grid.setVgap(5);             //Label1         Label lbl1 = new Label("Number of days on the trip: ");         GridPane.setConstraints(lbl1, 0, 0);         GridPane.setRowIndex(lbl1, 0);         lbl1.setFont(font);         //Label 2         Label lbl2 = new Label("Amount of airfare: ");         GridPane.setConstraints(lbl2, 0, 0);         GridPane.setRowIndex(lbl2, 2);         lbl2.setFont(font);         //Label 3         Label lbl3 = new Label("Amount of car rental fees: ");         GridPane.setConstraints(lbl3, 0, 0);         GridPane.setRowIndex(lbl3, 4);         lbl3.setFont(font);         //Label 4         Label lbl4 = new Label("Number of miles driven:");         GridPane.setConstraints(lbl4, 0, 0);         GridPane.setRowIndex(lbl4, 7);         lbl4.setFont(font);         //Label 5         Label lbl5 = new Label("Amount of parking fees:");         GridPane.setConstraints(lbl5, 0, 0);         GridPane.setRowIndex(lbl5, 9);         lbl5.setFont(font);         //Label 6         Label lbl6 = new Label("Amount of taxi charges:");         GridPane.setConstraints(lbl6, 0, 0);         GridPane.setRowIndex(lbl6, 11);         lbl6.setFont(font);         //label 7         Label lbl7 = new Label("Conference registration:");         GridPane.setConstraints(lbl7, 0, 0);         GridPane.setRowIndex(lbl7, 13);         lbl7.setFont(font);         //label 8         Label lbl8 = new Label("Lodging charges:");         GridPane.setConstraints(lbl8, 0, 0);         GridPane.setRowIndex(lbl8, 15);         lbl8.setFont(font);         //selection label         Label lbl10 = new Label("Selection:");         GridPane.setConstraints(lbl10,0,0);         GridPane.setRowIndex(lbl10,20);         lbl10.setFont(font);          //info correct label         Label lbl11= new Label("This information is correct:");         GridPane.setConstraints(lbl11,0,0);         GridPane.setRowIndex(lbl11,22);         lbl11.setFont(font);            //create personal radio button         RadioButton button1 = new RadioButton("Personal Vehicle used?");         button1.setFont(font);         button1.setOnAction(e -> {             textMilesDriven.setDisable(!button1.isSelected());             if (!button1.isSelected()) {                 textMilesDriven.setText("");             }         });         GridPane.setConstraints(button1, 0, 0);         GridPane.setRowIndex(button1, 6);           //Textfield1         textDays = new TextField("");         textDays.setPrefWidth(110);         GridPane.setConstraints(textDays, 0, 0);         GridPane.setRowIndex(textDays, 1);          //textfield 2         textAirFare = new TextField("");         textAirFare.setPrefWidth(110);         GridPane.setConstraints(textAirFare, 0, 0);         GridPane.setRowIndex(textAirFare, 3);         //textfield 3         textCarRental = new TextField("");         textCarRental.setPrefWidth(110);         GridPane.setConstraints(textCarRental, 0, 0);         GridPane.setRowIndex(textCarRental, 5);         //textfield 4         textMilesDriven = new TextField("");         textMilesDriven.setPrefWidth(110);         //Disable textfield unless user choose radiobutton         textMilesDriven.setDisable(!button1.isSelected());         GridPane.setConstraints(textMilesDriven, 0, 0);         GridPane.setRowIndex(textMilesDriven, 8);         //textfield 5         textParkingFees = new TextField("");         textParkingFees.setPrefWidth(110);         GridPane.setConstraints(textParkingFees, 0, 0);         GridPane.setRowIndex(textParkingFees, 10);         //textfield 6         textTaxiCharges = new TextField("");         textTaxiCharges.setPrefWidth(110);         GridPane.setConstraints(textTaxiCharges, 0, 0);         GridPane.setRowIndex(textTaxiCharges, 12);         //textfield 7         textRegisFees = new TextField("");         textRegisFees.setPrefWidth(110);         GridPane.setConstraints(textRegisFees, 0, 0);         GridPane.setRowIndex(textRegisFees, 14);         //textfield 8         textLodgingCharges = new TextField("");         textLodgingCharges.setPrefWidth(110);         GridPane.setConstraints(textLodgingCharges, 0, 0);         GridPane.setRowIndex(textLodgingCharges, 16);         //selection textfield         textSelection = new TextField("");         textSelection.setPrefWidth(110);         GridPane.setConstraints(textSelection,0,0);         GridPane.setRowIndex(textSelection,20);         GridPane.setColumnIndex(textSelection,1);         textSelection.setText("Regular");         textSelection.setEditable(false);         textSelection.setFont(font);           //Assign all values for combo box         comboBox = new ComboBox<>();         comboBox.getItems().addAll("Regular", "Espresso", "Latte", "Frappucino", "Mocha");         comboBox.setOnAction(e -> textSelection.setText(comboBox.getValue()));         comboBox.setValue("Regular");          //correct checkbox         correctCheckBox = new CheckBox();         grid.add(correctCheckBox,1,22);               VBox layout = new VBox(10);         Label lbl9 = new Label("Select Favorite Coffee:");         lbl9.setFont(font);         GridPane.setConstraints(lbl9, 0, 0);         GridPane.setRowIndex(lbl9, 18);         GridPane.setColumnIndex(lbl9,0);            layout.setPadding(new Insets(20, 20, 20, 20));         layout.getChildren().addAll(comboBox);         scene = new Scene(layout, 400, 600);         GridPane.setConstraints(layout, 0, 0);         GridPane.setRowIndex(layout, 19);         GridPane.setColumnIndex(comboBox,1);            //Reset Button         resetButton = new Button("Reset");         resetButton.setFont(font);         resetButton.setOnAction(e -> reset());         GridPane.setConstraints(resetButton,0,0);         GridPane.setRowIndex(resetButton,25);         GridPane.setColumnIndex(resetButton,0);            //Calculate Button         btn = new Button("Calculate Reimbursement");         btn.setFont(font);         GridPane.setConstraints(btn, 0, 0);         GridPane.setRowIndex(btn, 25);         GridPane.setColumnIndex(btn,1);         grid.getChildren().addAll(lbl1, lbl2, lbl3, lbl4, lbl5, lbl6, lbl7, lbl8, lbl9,lbl10,lbl11,                 textDays, textAirFare, textCarRental, textMilesDriven, textParkingFees, textTaxiCharges,                 textRegisFees, textLodgingCharges,textSelection, btn, button1, layout,resetButton);         btn.setOnAction(this);         /**          * start the scene          */         Scene scene = new Scene(grid, 300, 600);         primaryStage.setTitle("Reimbursement");         primaryStage.setScene(scene);         primaryStage.show();      }     private void reset(){         textCarRental.setText("");         textDays.setText("");         textMilesDriven.setText("");         textLodgingCharges.setText("");         textRegisFees.setText("");         textTaxiCharges.setText("");         textParkingFees.setText("");         comboBox.setValue(comboBox.getItems().get(0));         textSelection.setText(comboBox.getItems().get(0));       }       @Override     public void handle(ActionEvent event) {         double days, airfare, carRental, miles, milesdriven, parking, taxi, conference, lodging, travelExpenses, paidAmount;         double allowableExpenses = 506.25;         double meals = 37.00;         double parkingFees = 10.00;         double taxiCharges = 20.00;         double lodgingCharges = 95.00;         double carRent = 0.27;          //decimal format         DecimalFormat dollar = new DecimalFormat("$#,##0.00");              days = Integer.parseInt(textDays.getText());              airfare = Double.parseDouble(textAirFare.getText());             carRental = Double.parseDouble(textCarRental.getText());             miles = Double.parseDouble(textMilesDriven.getText());             parking = Double.parseDouble(textParkingFees.getText());             taxi = Double.parseDouble(textTaxiCharges.getText());             conference = Double.parseDouble(textRegisFees.getText());             lodging = Double.parseDouble(textLodgingCharges.getText());              milesdriven = miles * carRent;              travelExpenses = days * lodging + carRental + airfare + parking + taxi + conference;             paidAmount = travelExpenses - allowableExpenses;              if (paidAmount < 0) {                 paidAmount = 0;             }               Alert alert = new Alert(Alert.AlertType.INFORMATION);             if (event.getSource() == btn) {                 alert.setTitle("Message");                 alert.setHeaderText("");                 alert.setContentText(String.format("Total Expenses: $%s " +                         "Allowable Expenses: $%s Amount to be paid: $%s", travelExpenses, allowableExpenses, paidAmount));                 alert.showAndWait();             }          }      public static void main(String[] args) {         launch(args);     } } 

Explanation / Answer

Since the input to the calculator field is blank, so it will consider the value as null and it will throw an exception while a parsing a null value. This exception need to be handle as follow.

try {

} catch ( Exception e) {

//Add the code to handle exception.

}

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