I cannot get this to show up when I run it and I can't figure out whats wrong.

import java.applet.*;
    import java.awt.*;
    import java.awt.event.*;
    import java.text.*;
    import javax.swing.*;

        public class TravelCostEstimator extends Frame implements ActionListener,ItemListener
    {
        //This part defines how the program will look
        Panel partOnePanel = new Panel();
            Label companyLabel = new Label("Traveler's Gasoline Calculator");
            Label milesLabel = new Label("\nAnticipated Miles");
                TextField milesField = new TextField(10);
            Label costPerGallonLabel = new Label("\nAnticipated Per Gallon Cost Of Gas");
                TextField costPerGallonField = new TextField(10);
            Label milesPerGallonLabel = new Label("\nVehicle Miles Per Gallon");
                TextField milesPerGallonField = new TextField(10);
            Button calcButton = new Button("Calculate");
        Panel partTwoPanel = new Panel();
            Label beginningLocationLabel = new Label("\nBeginning Location");
            Label endLocationLabel = new Label("\n Destination");
            Label vehicleSizeLabel = new Label("\n Type of Vehicle");
            Label gasTypeLabel = new Label("\n Type of Gas");
            Button submitButton = new Button("Submit");
            Button clearButton = new Button("Clear");


        //This serves as the main method used by the main class
        public static void main(String[] args)
        {

            TravelCostEstimator f = new TravelCostEstimator();
            f.setBounds(200,200,600,300);
            f.setTitle("Traveler's Gasoline Calculator");
            f.setVisible(true);


            double totalOilChangeCost, totalFuelCost, totalTravelExpense, fuelPrice;
            double oilChangeCost = 30.00;
            double fuelSupeUnleadedCost = 3.00;
            double fuelUnleadedCost = 2.90;
            double fuelLeadedCost = 2.50;
            double fuelDieselCost = 4.00;
            int distanceTravel, milesPerTank, tankCapacity, milesEntered;
            int oilChangeRequired = 3000;
            int vehicleCompactTankCapacity = 13;
            int vehicleMidSizeTankCapacity = 18;
            int vehicleLuxuryTankCapacity = 15;
            int vehicleSUVTankCapacity = 23;
            int totalOilChange = 0;
            char vehicleLabel, fuelLabel, vehicleLabelSelected, fuelLabelSelected;
            int totalMiles, milesPerGallon, mpg;
            double oilChange = 30.00, fuelCost,totalCost, costPerMile, fuel, total, numOfGallons;
        }

        public void init()
        {
            // Sets the layout with two panels
            this.setLayout(new BorderLayout());
                partOnePanel.setLayout(new FlowLayout());
                partTwoPanel.setLayout(new FlowLayout());

            //adds components to partOne panel
            setBackground(Color.red);
            partOnePanel.add(companyLabel);
            partOnePanel.add(milesLabel);
            partOnePanel.add(milesField);
            partOnePanel.add(costPerGallonLabel);
            partOnePanel.add(costPerGallonField);
            partOnePanel.add(milesPerGallonLabel);
            partOnePanel.add(milesPerGallonField);
            partOnePanel.add(calcButton);
                calcButton.addActionListener(this);

            //adds compponents to partTwo panel
            partTwoPanel.add(beginningLocationLabel);
                Choice beginningLocation = new Choice();
                beginningLocation.addItemListener(this);
                    beginningLocation.add("St. Cloud, MN");
                    beginningLocation.add("New York, NY");
                    beginningLocation.add("Dallas, TX");
                    beginningLocation.add("Minneapolis, MN");
                    beginningLocation.add("Las Vegas, NV");
                    beginningLocation.add("Miami, FL");
            partTwoPanel.add(endLocationLabel);
                Choice endLocationChoice = new Choice();
                endLocationChoice.addItemListener(this);
                    endLocationChoice.add("Seattle, WA");
                    endLocationChoice.add("Denver, CO");
                    endLocationChoice.add("Tampa, FL");
                    endLocationChoice.add("Atlanta, GA");
                    endLocationChoice.add("Chicago, IL");
                    endLocationChoice.add("Boston, MA");
            partTwoPanel.add(vehicleSizeLabel);
                Choice vehicleSizeChoice = new Choice();
                vehicleSizeChoice.addItemListener(this);
                    vehicleSizeChoice.add("Compact");
                    vehicleSizeChoice.add("Mid-Size");
                    vehicleSizeChoice.add("Luxury");
                    vehicleSizeChoice.add("SUV");
            partTwoPanel.add(gasTypeLabel);
                Choice gasTypeChoice = new Choice();
                gasTypeChoice.addItemListener(this);
                    gasTypeChoice.add("Leaded");
                    gasTypeChoice.add("Unleaded");
                    gasTypeChoice.add("Super Unleaded");
                    gasTypeChoice.add("Diesel");
            partTwoPanel.add(submitButton);
                submitButton.addActionListener(this);
            partTwoPanel.add(clearButton);
                clearButton.addActionListener(this);

            //adds panels to the frame
            add(partOnePanel, BorderLayout.NORTH);
            add(partTwoPanel, BorderLayout.CENTER);
        }


        public void actionPerformed (ActionEvent e)
        {
        }

        public void itemStateChanged(ItemEvent ie)
        {
        }
}

Here is my updated code. I know I need some kind of listener for my 4 JComboBox. What kind of listener do I need and how do I make it usable in my program?

import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
import java.util.*;


public class TravelerGasolineCalculator extends JFrame implements ActionListener
{
    //declare variables
    int totalMiles, mpg;
    double oilChange = 30.00, fuelCost, totalCost, costPerMile, fuel, total, numOfGallons;
    double superUnleadedCost=3.00, unleadedCost=2.90, leadedCost=2.50, dieselCost=4.00;
    int compactTank=13,midSizeTank=18, luxuryTank=15,suvTank=23;
    String location[] = {"New York, NY","Minneapolis, MN", "Boise, ID", "Dallas, TX", "Miami, FL", "Las Vegas, NV"};
    String locationTwo[] = {"New York, NY","Minneapolis, MN", "Boise, ID", "Dallas, TX", "Miami, FL", "Las Vegas, NV"};
    String vehicle[] = {"Compact", "Mid-Size", "Luxury", "SUV"};
    String fuelPrice[] = {"Leaded", "Unleaded", "Super Unleaded", "Diesel"};

    //COnstruct a panel for each row
    JPanel firstRow = new JPanel();
    JPanel secondRow = new JPanel();
    JPanel thirdRow = new JPanel();
    JPanel fourthRow = new JPanel();
    JPanel fifthRow = new JPanel();
    JPanel sixthRow = new JPanel();
    JPanel seventhRow = new JPanel();
    JPanel eighthRow = new JPanel();
    JPanel ninthRow = new JPanel();
    JPanel tenthRow = new JPanel();


    //Construct a panel for the fields and button
    JPanel fieldPanelOne = new JPanel();
    JPanel fieldPanelTwo = new JPanel();
    JPanel buttonPanelOne = new JPanel();
    JPanel buttonPanelTwo = new JPanel();

    //Construct labels and texts boxes
    JLabel milesLabel = new JLabel("Anticipated Miles:");
        JTextField miles = new JTextField(10);
    JLabel costPerGallonLabel = new JLabel("Cost Per Gallon");
        JTextField costPerGallon = new JTextField(10);
    JLabel milesPerGallonLabel = new JLabel("Miles Per Gallon");
        JTextField milesPerGallon = new JTextField(10);
    JLabel calcLabel = new JLabel("           Press the Calculate button");
    JLabel beginningLocationLabel = new JLabel("Beginning Location");
        JComboBox cityBox = new JComboBox(location);
    JLabel destinationLabel = new JLabel("Destination");
        JComboBox cityBoxTwo = new JComboBox(locationTwo);
    JLabel vehicleSizeLabel = new JLabel("Vehicle Size");
        JComboBox vehicleBox = new JComboBox(vehicle);
    JLabel fuelLabel = new JLabel("Fuel Type");
        JComboBox fuelBox = new JComboBox(fuelPrice);
    JLabel submitLabel = new JLabel("Press the Submit Button");



    // Construct button
    JButton calcButton = new JButton("Calculate");
    JButton submitButton = new JButton("Submit");
    JButton clearButton = new JButton("Clear");

    public static void main(String[] args)
    {
        //set the look of the interface
        try
        {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.motif.MotifLookAndFeel");
        }
        catch(Exception e)
        {
            JOptionPane.showMessageDialog(null,"The Traveler's Gasoline Calculator could not set the Look and Feel.","Error", JOptionPane.INFORMATION_MESSAGE);
        }

        TravelerGasolineCalculator f = new TravelerGasolineCalculator();
        f.setSize(450,400);
        f.setTitle("Traveler's Gasoline Calculator");
        f.setResizable(true);
        f.setLocation(200,200);
        f.setVisible(true);
    }

    public TravelerGasolineCalculator()
    {
        Container c = getContentPane();
        c.setLayout((new BorderLayout()));
        fieldPanelOne.setLayout(new GridLayout(4,2));
        FlowLayout rowSetup = new FlowLayout(FlowLayout.LEFT,5,3);
            firstRow.setLayout(rowSetup);
            secondRow.setLayout(rowSetup);
            thirdRow.setLayout(rowSetup);
            fourthRow.setLayout(rowSetup);
        fieldPanelTwo.setLayout(new GridLayout(5,2));
            fifthRow.setLayout(rowSetup);
            sixthRow.setLayout(rowSetup);
            seventhRow.setLayout(rowSetup);
            eighthRow.setLayout(rowSetup);
            ninthRow.setLayout(rowSetup);
            tenthRow.setLayout(rowSetup);
        buttonPanelOne.setLayout(new FlowLayout(FlowLayout.CENTER));

        //Add Fields to rows
        firstRow.add(milesLabel);
        firstRow.add(miles);

        secondRow.add(costPerGallonLabel);
        secondRow.add(costPerGallon);

        thirdRow.add(milesPerGallonLabel);
        thirdRow.add(milesPerGallon);

        fourthRow.add(calcLabel);

        fifthRow.add(beginningLocationLabel);
        fifthRow.add(cityBox);

        sixthRow.add(destinationLabel);
        sixthRow.add(cityBoxTwo);

        seventhRow.add(vehicleSizeLabel);
        seventhRow.add(vehicleBox);

        eighthRow.add(fuelLabel);
        eighthRow.add(fuelBox);

        ninthRow.add(submitLabel);


        //Adds rows to panel
        fieldPanelOne.add(firstRow);
        fieldPanelOne.add(secondRow);
        fieldPanelOne.add(thirdRow);
        fieldPanelOne.add(fourthRow);
        fieldPanelTwo.add(fifthRow);
        fieldPanelTwo.add(sixthRow);
        fieldPanelTwo.add(seventhRow);
        fieldPanelTwo.add(eighthRow);
        fieldPanelTwo.add(ninthRow);

        //adds button to panel
        buttonPanelOne.add(calcButton);
        buttonPanelOne.add(submitButton);
        buttonPanelOne.add(clearButton);

        //Adds panels to frame
        c.add(fieldPanelOne, BorderLayout.NORTH);
        c.add(fieldPanelTwo, BorderLayout.CENTER);
        c.add(buttonPanelOne, BorderLayout.SOUTH);

        //adds funtion to buttons
        calcButton.addActionListener(this);
        submitButton.addActionListener(this);
        clearButton.addActionListener(this);
    }

    public void actionPerformed(ActionEvent e)
    {
        //Calculates total cost with or without an oil change
        fuel = Double.parseDouble (costPerGallon.getText());
        mpg = Integer.parseInt (milesPerGallon.getText());
        total = Double.parseDouble (miles.getText());
        numOfGallons = total/mpg;
        totalCost = numOfGallons*fuel;
        costPerMile = totalCost/total;

        DecimalFormat twoDigit = new DecimalFormat("$#,###.##");

                if (total < 3000)
                {
                    JOptionPane.showMessageDialog(null,"Your approximate cost of the trip is " + twoDigit.format(totalCost) + ".","Approximate Cost",JOptionPane.INFORMATION_MESSAGE);
                }

                else
                {
                    totalCost = numOfGallons * fuel + oilChange;
                    costPerMile = totalCost/total;

                    JOptionPane.showMessageDialog(null,"Your total cost of the trip is " + twoDigit.format(totalCost) + ".","Cost With Oil Change", JOptionPane.INFORMATION_MESSAGE);
                }
    }

}
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