Question

I am using IntelliJ IDEA with JavaFX to build a travel expensive calculator, but somehow it 

wouldn't calculate total expensive? It was working until I add the TextFieldListener because I need to make sure user

only input either mile driven or airfareCost. Please help me figure out what I did wrong.

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.EventHandler;
import javafx.fxml.FXMLLoader;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Parent;
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.scene.layout.HBox;
import javafx.stage.Stage;

public class Main extends Application {

    TextField field1, field2, field3, field4, field5, field6;
    Button submitButton, cancelButton;

    @Override
    public void start(Stage primaryStage) throws Exception{

        Label label1 = new Label ("(1) Number of days on the trip");
        Label label2 = new Label ("(2) Transportation cost (choose one only)");
        Label label3 = new Label ("Airfare Cost ");
        Label label4 = new Label ("Miles driven  ");
        Label label5 = new Label ("(3) Conference registration cost ");
        Label label6 = new Label ("(4) Lodging Cost (per night) ");
        Label label7 = new Label ("(5) Food cost (total) ");
        Label TotalExpensive = new Label("Total expenses: ");
        Label TotalExpensiveResult = new Label(" ");
        Label TotalCost = new Label("How much you own: ");
        Label TotalCostResult = new Label(" ");

        field1 = new TextField();
        field2 = new TextField();
        field3 = new TextField();
        field4 = new TextField();
        field5 = new TextField();
        field6 = new TextField();//all textfield

        submitButton = new Button ("Submit"); //Create submit button
        submitButton.setDisable( true);
        cancelButton = new Button ("Cancel"); //Create Cancel button


        HBox hBox = new HBox(20, label1, field1);
        HBox hBox1 = new HBox(10, label2);
        HBox hBox2 = new HBox(15, label3, field2);
        HBox hBox3 = new HBox(10, label4, field3);
        HBox hBox4 = new HBox(12, label5, field4);
        HBox hBox5 = new HBox(32, label6, field5);
        HBox hBox6 = new HBox(75, label7, field6);
        HBox hBox7 = new HBox(20, submitButton, cancelButton);
        HBox hBox8 = new HBox(20, TotalExpensive, TotalExpensiveResult);
        HBox hBox9 = new HBox(20, TotalCost, TotalCostResult);


        hBox.setAlignment(Pos.BASELINE_RIGHT); //Alignment
        hBox1.setAlignment(Pos.BASELINE_LEFT);
        hBox2.setAlignment(Pos.BASELINE_RIGHT);
        hBox3.setAlignment(Pos.BASELINE_RIGHT);
        hBox4.setAlignment(Pos.BASELINE_RIGHT);
        hBox5.setAlignment(Pos.BASELINE_RIGHT);
        hBox6.setAlignment(Pos.BASELINE_RIGHT);
        hBox7.setAlignment(Pos.CENTER);
        hBox8.setAlignment(Pos.BASELINE_LEFT);
        hBox9.setAlignment(Pos.BASELINE_LEFT);



        hBox1.setPadding(new Insets(0,0,15,0));
        hBox3.setPadding(new Insets(0,0,15,0));
        hBox7.setPadding(new Insets(15,0,0,0));
        hBox8.setPadding(new Insets(0,0,15,0));
        hBox9.setPadding(new Insets(0,0,15,0));

        TextFieldListener listener = new TextFieldListener();
        field1.textProperty().addListener(listener);
        field2.textProperty().addListener(listener);
        field3.textProperty().addListener(listener);
        field4.textProperty().addListener(listener);
        field5.textProperty().addListener(listener);
        field6.textProperty().addListener(listener);



        GridPane gridPane = new GridPane ();

        gridPane.add(hBox, 0, 0);
        gridPane.add(hBox1, 0, 1);
        gridPane.add(hBox2, 0, 2);
        gridPane.add(hBox3, 0, 3);
        gridPane.add(hBox4, 0, 4);
        gridPane.add(hBox5, 0, 5);
        gridPane.add(hBox6, 0, 6);
        gridPane.add(hBox7, 0, 7);
        gridPane.add(hBox8, 0, 8);
        gridPane.add(hBox9, 0, 9);
        gridPane.setAlignment(Pos.CENTER);
        gridPane.setPadding( new Insets(20, 20, 20, 20));
        gridPane.setVgap( 10);
        gridPane.setHgap( 10);
        primaryStage.setTitle("Travel Expenses Calculator");
        primaryStage.setScene(new Scene (gridPane));
        primaryStage.show();

        submitButton.setOnAction(event ->
        {

            double days = Double.parseDouble(field1.getText());
            double airFare = Double.parseDouble(field2.getText());
            double miles = Double.parseDouble(field3.getText());
            double ConregCost = Double.parseDouble(field4.getText());
            double lodgingCost = Double.parseDouble(field5.getText());
            double foodCost = Double.parseDouble(field6.getText());

            TotalExpensiveResult.setText(" " + ( airFare+ foodCost + ConregCost + (days * lodgingCost)) );

        });





    }

    private class TextFieldListener implements ChangeListener<String>
    {
        @Override
        public void changed(ObservableValue<? extends String> source, String oldValue, String
                newValue)
        {
            String numTrip = field1.getText();
            String airFare = field2.getText();
            String miles = field3.getText();
            String confCost = field4.getText();
            String lodgingCost = field5.getText();
            String foodCost = field6.getText();

            if (airFare.trim().equals( "")  )
            {
                submitButton.setDisable(numTrip.trim().equals( "") ||miles.trim().equals( "") || confCost.trim().equals( "")||
                        lodgingCost.trim().equals( "")|| foodCost.trim().equals( ""));
            }

            else if (miles.trim().equals( "") )
            {
                submitButton.setDisable(numTrip.trim().equals( "") ||airFare.trim().equals( "") || confCost.trim().equals( "")||
                        lodgingCost.trim().equals( "")|| foodCost.trim().equals( ""));
            }

            else
            {
                submitButton.setDisable( true);
            }


        }
    };




    public static void main(String[] args) {
        launch(args);
    }
}

Answer 1

Either mile driven or air fare cost is going to remain empty, as per your requirement. But, on clicking the submit button, you are parsing both the fields. This is causing an parsing related exception while parsing one of the fields [Double.parseDouble()]. Checking for non-empty values before parsing will resolve the issue. Here is the modified setOnAction method. Also, found that the 'miles' variable is not used in the calculation.

submitButton.setOnAction(event ->
{

    double days = Double.parseDouble(field1.getText());
    String field2Str = field2.getText();
    double airFare = field2Str == null || field2Str.trim().isEmpty() ? 0 : Double.parseDouble(field2Str.trim());
    String field3Str = field3.getText();
    double miles = field3Str == null || field3Str.trim().isEmpty() ? 0 : Double.parseDouble(field3Str.trim());
    double ConregCost = Double.parseDouble(field4.getText());
    double lodgingCost = Double.parseDouble(field5.getText());
    double foodCost = Double.parseDouble(field6.getText());

    TotalExpensiveResult.setText(" " + ( airFare+ foodCost + ConregCost + (days * lodgingCost)) );

});

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