import javax.swing.$*$;

import java.awt.event.$*$;

$//$ Immutable class that calculates the trip cost

class TripCost $\{$

private final double distance;

private final double gasCost;

private final double gasMileage;

private final int numDays;

private final double hotelCost;

private final double foodCost;

private final double attractionsCost;

public TripCost$($double distance, double gasCost, double gasMileage, int numDays, double hotelCost, double foodCost, double attractionsCost$)\{$

this.distance $=$ distance;

this.gasCost $=$ gasCost;

this.gasMileage $=$ gasMileage;

this.numDays $=$ numDays;

this.hotelCost $=$ hotelCost;

this.foodCost $=$ foodCost;

this.attractionsCost $=$ attractionsCost;

$\}$

public double calculateTotalTripCost$()\{$

double gasolineCost $=($distance $/$ gasMileage$)*$ gasCost;

return gasolineCost $+(($hotelCost $+$ foodCost$)*$ numDays$)+$ attractionsCost;

$\}$

$\}$

$//$ GUI class

public class Project$3$ extends JFrame $\{$

private JTextField txtDistance, txtGasolineCost, txtGasMileage, txtNumDays, txtHotelCost, txtFoodCost, txtAttractions;

private JComboBox cmbDistance, cmbGasolineCost, cmbGasMileage;

private JButton btnCalculate;

private JTextField txtTotalCost;

public Project$3()\{$

$//$ Initialize the components

txtDistance $=$ new JTextField$()$;

txtGasolineCost $=$ new JTextField$()$;

txtGasMileage $=$ new JTextField$()$;

txtNumDays $=$ new JTextField$()$;

txtHotelCost $=$ new JTextField$()$;

txtFoodCost $=$ new JTextField$()$;

txtAttractions $=$ new JTextField$()$;

txtTotalCost $=$ new JTextField$()$;

txtTotalCost.setEditable$($false$)$;

$//$ Combo boxes with options

cmbDistance $=$ new JComboBox$<>($new String$[]\{"$miles$",$ "kilometers"$\})$;

cmbGasolineCost $=$ new JComboBox$<>($new String$[]\{"$dollars$/$gal$",$ "dollars$/$litre$"\})$;

cmbGasMileage $=$ new JComboBox$<>($new String$[]\{"$miles$/$gallon$",$ "kilometers$/$litre$"\})$;

btnCalculate $=$ new JButton$("$Calculate$")$;

btnCalculate.addActionListener$($new ActionListener$()\{$

public void actionPerformed$($ActionEvent e$)\{$

calculateCost$()$;

$\}$

$\})$;

$//$ Layout for the GUI components

setLayout$($new BoxLayout$($getContentPane$(),$ BoxLayout.Y$\_$AXIS$))$;

add$($new JLabel$("$Distance:$"))$;

add$($txtDistance$)$;

add$($cmbDistance$)$;

add$($new JLabel$("$Gasoline Cost:"$))$;

add$($txtGasolineCost$)$;

add$($cmbGasolineCost$)$;

add$($new JLabel$("$Gas Mileage:"$))$;

add$($txtGasMileage$)$;

add$($cmbGasMileage$)$;

add$($new JLabel$("$Number Of Days:"$))$;

add$($txtNumDays$)$;

add$($new JLabel$("$Hotel Cost:"$))$;

add$($txtHotelCost$)$;

add$($new JLabel$("$Food Cost:"$))$;

add$($txtFoodCost$)$;

add$($new JLabel$("$Attractions:$"))$;

add$($txtAttractions$)$;

add$($btnCalculate$)$;

add$($new JLabel$("$Total Trip Cost"$))$;

add$($txtTotalCost$)$;

$//$ Setting up the frame

setTitle$("$Trip Cost Estimator"$)$;

setDefaultCloseOperation$($JFrame$.$EXIT$\_$ON$\_$CLOSE$)$;

pack$()$;

setVisible$($true$)$;

$\}$

private void calculateCost$()\{$

$//$ Parse user input and perform conversions if necessary

double distance $=$ Double.parseDouble$($txtDistance$.$getText$())$;

distance $=$ cmbDistance.getSelectedItem$().$equals$("$kilometers$")?$ distance $*0\mathrm{.}621371$ : distance; $//$ Convert to miles if necessary

double gasCost $=$ Double.parseDouble$($txtGasolineCost$.$getText$())$;

gasCost $=$ cmbGasolineCost.getSelectedItem$().$equals$("$dollars$/$litre$")?$ gasCost $*3\mathrm{.}78541$ : gasCost; $//$ Convert to dollars$/$gallon if necessary

double gasMileage $=$ Double.parseDouble$($txtGasMileage$.$getText$())$;

gasMileage $=$ cmbGasMileage.getSelectedItem$().$equals$("$kilometers$/$litre$")?$ gasMileage $*2\mathrm{.}35215$ : gasMileage; $//$ Convert to miles$/$gallon if necessary

int numDays $=$ Integer.parseInt$($txtNumDays$.$getText$())$;

double hotelCost $=$ Double.parseDouble$($txtHotelCost$.$getText$())$;

double foodCost $=$ Double.parseDouble$($txtFoodCost$.$getText$())$;

double attractionsCost $=$ Double.parseDouble$($txtAttractions$.$getText$())$;

$//$ Create a TripCost object and calculate the total cost

TripCost tripCost $=$ new TripCost$($distance$,$ gasCost, gasMileage, numDays, hotelCost, foodCost, attractionsCost$)$;

double totalCost $=$ tripCost.calculateTotalTripCost$()$;

$//$ Display the total cost

txtTotalCost.setText$($String$.$format$("$$$\%\mathrm{.}2$f$",$ totalCost$))$;

$\}$

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

$//$ Run the GUI in the Event Dispatch Thread for thread safety

SwingUtilities.invokeLater$($new Runnable$()\{$

public void run$()\{$

new Project$3()$; $//$ Create and show the GUI

$\}$

$\})$;

$\}$

$\}$

Need a test plan and description of above program.