I have the main part of my code done but I don'T know if I should use an action listener or an event listener for my JComboBox. I have 4 JComboBoxes and only need to retrieve the info from my vehicleBox and fuelBox at this point. I need to take that information and make it equal the value I aleady have declared it and use it to figure out the total cost of a trip. I am a beginner at programming so if any help that you can give, please dumb it down to a level a beginner would understand. Thanks for any help you can offer.

Here is the code i have so far:

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, EventListener
{
    //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);

        //adds function to dropdown lists
        cityBox.addActionListener(this);
        cityBoxTwo.addActionListener(this);
        vehicleBox.addActionListener(this);
        fuelBox.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);
                }
    }

     public void itemStateChanged(ItemEvent ie)
     {
     }

}

depends on the action on which you want something performed. when selecting a new value in a dropdownlist? after clicking a button? after typing a character in a textfield?

I think you can get the content of combobox by using following things.

public void actionPerformed(ActionEvent e) {
        JComboBox cb = (JComboBox)e.getSource();
        String petName = (String)cb.getSelectedItem();

It will retutn the string that you have selected on the combobox.

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