Why does this only work on designed comboBox and not on hardcoded swing?

Question

Newbie question:

So this code here

public void comboItemItemStateChanged(java.awt.event.ItemEvent evt) {  
        ArrayList<String> arrayItem = new ArrayList<>();
        Iterator<String> iter;
        if(comboGroup.getSelectedItem().equals("Betta Fish")){
            comboItem.removeAllItems();
            arrayItem.add("Plakat");
            arrayItem.add("Halfmoon");
            arrayItem.add("Crown Tail");
            arrayItem.add("Double Tail");
            iter = arrayItem.iterator();
            while(iter.hasNext()){
                comboItem.addItem(iter.next());
            }
        }
        else if(comboGroup.getSelectedItem().equals("Snails")){
            comboItem.removeAllItems();
            arrayItem.add("Apple Horn");
            arrayItem.add("RamsHorn");
            arrayItem.add("Pond Snail");
            arrayItem.add("Assassin Snail");
            iter = arrayItem.iterator();
            while(iter.hasNext()){
                comboItem.addItem(iter.next());
            }

works when I try it on comboBoxes from Design tab in NetBeans. But when I try to apply it to my coded ComboBox, I get a message from evt saying Unused method parameters should be removed. Can I get an explanation why and what is the alternative for hardcoded comboBox?

Purpose of code: a dynamic comboBox so whatever I pick from comboBox1 will have each own set of lists for comboBox2

NOTE: I also tried to change comboItemItemStateChanged to just itemStatChanged.

Source code of my project: https://github.com/kontext66/GuwiPos/blob/main/GuwiPos

Sorry for the confusion everyone, I do have a main class.

public class Main{
    
    public static void main(String[] args){
        
        new GuwiPos();
        new HelpWin();
        
    }
    
}

Main.java, GuwiPos.java

Answer 1

Your code (improved version - minus one ActionListener)

public class SwingApp {
    
    private static JComboBox<String> comboItem;
    private static JComboBox<String> productCombo;
    
    public static void main (String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            
            @Override
            public void run () {
                createAndShowGUI();
            }
        });
    }
    
    private static void createAndShowGUI () {
        
        JFrame frame = createMainFrame();
        
        JPanel bluePanel = createBluePanel();
        JPanel greenPanel = createGreenPanel();
        JPanel redPanel = createRedPanel();
        JPanel yellowPanel = createYellowPanel();
        
        frame.add(bluePanel);
        frame.add(greenPanel);
        frame.add(redPanel);
        frame.add(yellowPanel);
        frame.setVisible(true);
    }
    
    private static JFrame createMainFrame () {
        JFrame frame = new JFrame("Open Betta POS");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(null);
        frame.setSize(900, 590);
        frame.setResizable(false);
        return frame;
    }
    
    private static JPanel createBluePanel () {
        ComboSelectionListener productComboListener = new ComboSelectionListener();
        JPanel panel = new JPanel(null); // Sets layout manager to null which is a bad idea!
        String[] products =
            {"Select Item...", "Betta Fish", "Snails", "Supplies", "Food"};
        productCombo = new JComboBox<>(products);
        productCombo.setBounds(130, 35, 150, 40);
        productCombo.setActionCommand("selectProduct");
        productCombo.addActionListener(productComboListener);
        comboItem = new JComboBox<>();
        comboItem.setBounds(130, 85, 150, 40);
        
        // TextFields
        JTextField txtPrice = new JTextField();
        txtPrice.setBounds(130, 135, 150, 40);
        
        JTextField txtQty = new JTextField();
        txtQty.setBounds(130, 185, 150, 40);
        
        JTextField txtTotal = new JTextField();
        txtTotal.setBounds(130, 235, 150, 40);
        JLabel labelProduct = new JLabel();
        labelProduct.setText("Item Group");
        labelProduct.setBounds(10, 5, 100, 100);
        // Item
        JLabel labelItem = new JLabel();
        labelItem.setText("Item");
        labelItem.setBounds(10, 55, 100, 100);
        // Price
        JLabel labelPrice = new JLabel();
        labelPrice.setText("Price");
        labelPrice.setBounds(10, 105, 100, 100);
        // Qty
        JLabel labelQty = new JLabel();
        labelQty.setText("Quantity");
        labelQty.setBounds(10, 155, 100, 100);
        // Total
        JLabel labelTotal = new JLabel();
        labelTotal.setText("Total");
        labelTotal.setBounds(10, 205, 100, 100);
        
        panel.setBackground(Color.blue);
        panel.setBounds(0, 0, 300, 300); // x,y,width,height
        panel.add(txtQty);
        panel.add(txtTotal);
        panel.add(txtPrice);
        panel.add(comboItem);
        panel.add(productCombo);
        panel.add(labelProduct);
        panel.add(labelItem);
        panel.add(labelPrice);
        panel.add(labelQty);
        panel.add(labelTotal);
        return panel;
        
    }
    
    private static JPanel createGreenPanel () {
        JPanel panel = new JPanel(null);
        panel.setBackground(Color.green);
        panel.setBounds(0, 300, 300, 450);// x,y,width,length
        JButton buttonBasket = new JButton();
        buttonBasket.setBounds(0, 0, 300, 50);
        buttonBasket.setText("Add to Basket");
        buttonBasket.setFocusable(false);
        buttonBasket.setBorder(BorderFactory.createEtchedBorder());
        buttonBasket
            .addActionListener(e -> System.out.println("Added Item to Basket: "
                + productCombo.getSelectedItem() + "\n" + comboItem.getSelectedItem()));
        
        JButton buttonPay = new JButton();
        buttonPay.setText("PAY");
        buttonPay.setBounds(0, 50, 150, 100);
        buttonPay.setFocusable(false);
        buttonPay.setBorder(BorderFactory.createEtchedBorder());
        buttonPay.addActionListener(e -> System.out.println("Payment Success"));
        
        JButton buttonCancel = new JButton();
        buttonCancel.setText("CANCEL");
        buttonCancel.setBounds(0, 150, 150, 100);
        buttonCancel.setFocusable(false);
        buttonCancel.setBorder(BorderFactory.createEtchedBorder());
        buttonCancel
            .addActionListener(e -> System.out.println("Transaction Cancelled"));
        
        JButton buttonDiscount = new JButton();
        buttonDiscount.setText("Apply Discount?");
        buttonDiscount.setBounds(150, 50, 150, 50);
        buttonDiscount.setFocusable(false);
        buttonDiscount.setBorder(BorderFactory.createEtchedBorder());
        buttonDiscount
            .addActionListener(e -> System.out.println("20% Discount Applied"));
        
        JButton buttonHelp = new JButton();
        buttonHelp.setText("HELP");
        buttonHelp.setBounds(150, 100, 150, 100);
        buttonHelp.setFocusable(false);
        buttonHelp.setBorder(BorderFactory.createEtchedBorder());
        
        JButton buttonDelete = new JButton();
        buttonDelete.setText("DELETE");
        buttonDelete.setBounds(150, 200, 150, 50);
        buttonDelete.setFocusable(false);
        buttonDelete.setBorder(BorderFactory.createEtchedBorder());
        buttonDelete.addActionListener(e -> System.out.println("Item Deleted"));
        
        panel.add(buttonBasket);
        panel.add(buttonPay);
        panel.add(buttonCancel);
        panel.add(buttonDiscount);
        panel.add(buttonHelp);
        panel.add(buttonDelete);
        
        return panel;
    }
    
    private static JPanel createRedPanel () {
        JPanel panel = new JPanel(null);
        panel.setBackground(Color.red);
        panel.setBounds(300, 0, 600, 300); // x,y,width,length
        return panel;
    }
    
    private static JPanel createYellowPanel () {
        JPanel panel = new JPanel();
        panel.setBackground(Color.yellow);
        panel.setBounds(0, 300, 900, 450); // x,y,width,length
        return panel;
    }
    
    private static class ComboSelectionListener implements ActionListener {
        
        @Override
        public void actionPerformed (ActionEvent e) {
            JComboBox<String> comboGroup = (JComboBox<String>) e.getSource();
            
            ArrayList<String> arrayItem = new ArrayList<>();
            Iterator<String> iter;
            if (comboGroup.getSelectedItem().equals("Betta Fish")) {
                comboItem.removeAllItems();
                arrayItem.add("Plakat");
                arrayItem.add("Halfmoon");
                arrayItem.add("Crown Tail");
                arrayItem.add("Double Tail");
                iter = arrayItem.iterator();
                while (iter.hasNext()) {
                    comboItem.addItem(iter.next());
                }
            } else if (comboGroup.getSelectedItem().equals("Snails")) {
                comboItem.removeAllItems();
                arrayItem.add("Apple Horn");
                arrayItem.add("RamsHorn");
                arrayItem.add("Pond Snail");
                arrayItem.add("Assassin Snail");
                iter = arrayItem.iterator();
                while (iter.hasNext()) {
                    comboItem.addItem(iter.next());
                }
            } else if (comboGroup.getSelectedItem().equals("Supplies")) {
                comboItem.removeAllItems();
                arrayItem.add("Small Fine Net");
                arrayItem.add("Large Fine Net");
                arrayItem.add("Flaring Mirror");
                arrayItem.add("Aquarium Hose");
                iter = arrayItem.iterator();
                while (iter.hasNext()) {
                    comboItem.addItem(iter.next());
                }
            } else if (comboGroup.getSelectedItem().equals("Food")) {
                comboItem.removeAllItems();
                arrayItem.add("Tubifex");
                arrayItem.add("Daphnia");
                arrayItem.add("Optimum Pellets");
                iter = arrayItem.iterator();
                while (iter.hasNext()) {
                    comboItem.addItem(iter.next());
                }
            } else if (comboGroup.getSelectedItem().equals("Select Item...")) {
                comboItem.removeAllItems();
                arrayItem.add("Select Item...");
                iter = arrayItem.iterator();
                while (iter.hasNext()) {
                    comboItem.addItem(iter.next());
                }
            }
        }
    }
}

Improvements made (aside from fixing the main issue)

1. Created a Swing (main) class that is not a Swing component
2. Main class doesn't implement ActionListener
3. Used SwingUtilities to launch Swing Application
4. Created methods to encapsulate the details involving the creation of components
5. Minimized the scope of variables

Answer 2

It's quite simple, really.
The message is just NetBeans informing you that the code of method comboItemItemStateChanged does not reference the method parameter evt. It is not an error nor even a warning. You can ignore it. NetBeans displays these "hints" in its editor when you write code whereas NetBeans GUI builder generates code.

Note that method comboItemItemStateChanged will be called each time an item in the JComboBox is selected and also each time an item is de-selected. I'm guessing that you only want the code to run when an item is selected, hence the first line of method comboItemItemStateChanged should be

if (evt.getStateChange() == ItemEvent.SELECTED) {

and then you are referencing the method parameter and the "hint" will go away.

Refer to How to Write an Item Listener

Edit

I think maybe you would benefit from learning about GUI design. I have never seen one like yours. I would like to know how you arrived at that design. In any case, the below code addresses only the functionality whereby the list in comboItem adjusts depending on the selected item in comboGroup.

In my experience, removing and adding items to the JComboBox via methods removeAllItems and addItem, is very slow. It is much more efficient to simply replace the JComboBox model which is what I have done in the below code. For small lists such as yours, the difference will not be noticed but it increases as the lists get larger.

Also, the [JComboBox] selected item is in the evt parameter to method comboItemItemStateChanged.

Your original code did not add an item listener to comboGroup nor did it have a main method. I have added these in the below code. Note that the item listener is added via a method reference.

import javax.swing.JPanel;
import javax.swing.JLabel;
import javax.swing.BorderFactory;
import javax.swing.ComboBoxModel;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JComboBox;

import java.awt.Color;
import java.awt.EventQueue;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Vector;
import java.awt.event.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

/**
 *
 * @author kahbg
 */
public class GuwiPos extends JFrame implements ActionListener {
    public static final Map<String, ComboBoxModel<String>>  LISTS;

    JButton buttonBasket;
    JButton buttonHelp;
    JTextField txtGroup;
    JTextField txtItem;
    JTextField txtQty;
    JTextField txtTotal;
    JTextField txtPrice;
    JComboBox<String> comboGroup;
    JComboBox<String> comboItem;

    static {
        LISTS = new HashMap<>();
        Vector<String> v = new Vector<>();
        v.add("Plakat");
        v.add("Halfmoon");
        v.add("Crown Tail");
        v.add("Double Tail");
        ComboBoxModel<String> model = new DefaultComboBoxModel<>(v);
        LISTS.put("Betta Fish", model);
        v = new Vector<>();
        v.add("Apple Horn");
        v.add("RamsHorn");
        v.add("Pond Snail");
        v.add("Assassin Snail");
        model = new DefaultComboBoxModel<>(v);
        LISTS.put("Snails", model);
        v = new Vector<>();
        v.add("Small Fine Net");
        v.add("Large Fine Net");
        v.add("Flaring Mirror");
        v.add("Aquarium Hose");
        model = new DefaultComboBoxModel<>(v);
        LISTS.put("Supplies", model);
        v = new Vector<>();
        v.add("Tubifex");
        v.add("Daphnia");
        v.add("Optimum Pellets");
        model = new DefaultComboBoxModel<>(v);
        LISTS.put("Food", model);
    }

    GuwiPos() {

        // ComboBox
        String[] products = {"Select Item...", "Betta Fish", "Snails", "Supplies", "Food"};
        comboGroup = new JComboBox<String>(products);
        comboGroup.addItemListener(this::comboItemItemStateChanged);
        comboGroup.setBounds(130, 35, 150, 40);

        comboItem = new JComboBox<String>();
        comboItem.setBounds(130, 85, 150, 40);

        // TextFields
        txtPrice = new JTextField();
        txtPrice.setBounds(130, 135, 150, 40);

        txtQty = new JTextField();
        txtQty.setBounds(130, 185, 150, 40);

        txtTotal = new JTextField();
        txtTotal.setBounds(130, 235, 150, 40);

        // txtTotalAmt = new JTextField(); to code later on

        // txtPaid = new JTextField(); to code later on

        // txtChange = new JTextField(); to code later on

        // Labels
        // Product
        JLabel labelProduct = new JLabel();
        labelProduct.setText("Item Group");
        labelProduct.setBounds(10, 5, 100, 100);
        // Item
        JLabel labelItem = new JLabel();
        labelItem.setText("Item");
        labelItem.setBounds(10, 55, 100, 100);
        // Price
        JLabel labelPrice = new JLabel();
        labelPrice.setText("Price");
        labelPrice.setBounds(10, 105, 100, 100);
        // Qty
        JLabel labelQty = new JLabel();
        labelQty.setText("Quantity");
        labelQty.setBounds(10, 155, 100, 100);
        // Total
        JLabel labelTotal = new JLabel();
        labelTotal.setText("Total");
        labelTotal.setBounds(10, 205, 100, 100);

        // Buttons
        buttonBasket = new JButton();
        buttonBasket.setBounds(0, 0, 300, 50);
        buttonBasket.setText("Add to Basket");
        buttonBasket.setFocusable(false);
        buttonBasket.setBorder(BorderFactory.createEtchedBorder());
        buttonBasket.addActionListener(this);

        JButton buttonPay = new JButton();
        buttonPay.setText("PAY");
        buttonPay.setBounds(0, 50, 150, 100);
        buttonPay.setFocusable(false);
        buttonPay.setBorder(BorderFactory.createEtchedBorder());
        buttonPay.addActionListener(e -> System.out.println("Payment Success"));

        JButton buttonCancel = new JButton();
        buttonCancel.setText("CANCEL");
        buttonCancel.setBounds(0, 150, 150, 100);
        buttonCancel.setFocusable(false);
        buttonCancel.setBorder(BorderFactory.createEtchedBorder());
        buttonCancel.addActionListener(e -> System.out.println("Transaction Cancelled"));

        JButton buttonDiscount = new JButton();
        buttonDiscount.setText("Apply Discount?");
        buttonDiscount.setBounds(150, 50, 150, 50);
        buttonDiscount.setFocusable(false);
        buttonDiscount.setBorder(BorderFactory.createEtchedBorder());
        buttonDiscount.addActionListener(e -> System.out.println("20% Discount Applied"));

        JButton buttonHelp = new JButton();
        buttonHelp.setText("HELP");
        buttonHelp.setBounds(150, 100, 150, 100);
        buttonHelp.setFocusable(false);
        buttonHelp.setBorder(BorderFactory.createEtchedBorder());

        JButton buttonDelete = new JButton();
        buttonDelete.setText("DELETE");
        buttonDelete.setBounds(150, 200, 150, 50);
        buttonDelete.setFocusable(false);
        buttonDelete.setBorder(BorderFactory.createEtchedBorder());
        buttonDelete.addActionListener(e -> System.out.println("Item Deleted"));

        // Panels
        // Left contains item and price
        JPanel bluePanel = new JPanel();
        bluePanel.setBackground(Color.blue);
        bluePanel.setBounds(0, 0, 300, 300); // x,y,width,height
        bluePanel.setLayout(null);
        // Right contains product basket
        JPanel redPanel = new JPanel();
        redPanel.setBackground(Color.red);
        redPanel.setBounds(300, 0, 600, 300); // x,y,width,length
        redPanel.setLayout(null);
        // Bottom Left contains buttons pay,change,discount
        JPanel greenPanel = new JPanel();
        greenPanel.setBackground(Color.green);
        greenPanel.setBounds(0, 300, 300, 450);// x,y,width,length
        greenPanel.setLayout(null);
        // Bottom Right contains total amount
        JPanel yellowPanel = new JPanel();
        yellowPanel.setBackground(Color.yellow);
        yellowPanel.setBounds(0, 300, 900, 450);// x,y,width,length
        yellowPanel.setLayout(null);

        this.setTitle("Open Betta POS");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLayout(null);
        this.setSize(900, 590);
        this.setResizable(false);
        this.setVisible(true);

        // ADDED AWT
        bluePanel.add(txtQty);
        bluePanel.add(txtTotal);
        bluePanel.add(txtPrice);
        bluePanel.add(comboItem);
        bluePanel.add(comboGroup);
        bluePanel.add(labelProduct);
        bluePanel.add(labelItem);
        bluePanel.add(labelPrice);
        bluePanel.add(labelQty);
        bluePanel.add(labelTotal);
        greenPanel.add(buttonBasket);
        greenPanel.add(buttonPay);
        greenPanel.add(buttonCancel);
        greenPanel.add(buttonDiscount);
        greenPanel.add(buttonHelp);
        greenPanel.add(buttonDelete);
        this.add(bluePanel);
        this.add(redPanel);
        this.add(greenPanel);
        this.add(yellowPanel);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == buttonBasket) {
            System.out.println("Added Item to Basket: " + comboGroup.getSelectedItem() + "\n"
                    + comboItem.getSelectedItem());
        }
    }

    // This is not working
    public void comboItemItemStateChanged(java.awt.event.ItemEvent evt) {
        if (evt.getStateChange() == ItemEvent.SELECTED) {
            Object selection = evt.getItem();
            ArrayList<String> arrayItem = new ArrayList<>();
            Iterator<String> iter;
            if (selection.equals("Betta Fish")) {
                comboItem.setModel(LISTS.get("Betta Fish"));
            }
            else if (selection.equals("Snails")) {
                comboItem.setModel(LISTS.get("Snails"));
            }
            else if (selection.equals("Supplies")) {
                comboItem.setModel(LISTS.get("Supplies"));
            }
            else if (selection.equals("Food")) {
                comboItem.setModel(LISTS.get("Food"));
            }
            else if (selection.equals("Select Item...")) {
                comboItem.removeAllItems();
                arrayItem.add("Select Item...");
                iter = arrayItem.iterator();
                while (iter.hasNext()) {
                    comboItem.addItem(iter.next());
                }
            }
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> new GuwiPos());
    }
}