Java Inventory Management Application with CRUD and SQL Functionality

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

// Data Access Object class for inventory operations
public class InventoryDAO {
    private Connection connection; // Connection object to interact with the database

    // Constructor to establish connection using DatabaseConnection class
    public InventoryDAO() {
        connection = DatabaseConnection.getConnection();
    }

    // Method to add a new inventory item
    public void addItem(InventoryItem item) {
        String query = "INSERT INTO inventory (name, quantity, price) VALUES (?, ?, ?)"; // SQL query to insert item
        try (PreparedStatement stmt = connection.prepareStatement(query)) {
            stmt.setString(1, item.getName()); // Set item name
            stmt.setInt(2, item.getQuantity()); // Set item quantity
            stmt.setDouble(3, item.getPrice()); // Set item price
            stmt.executeUpdate(); // Execute the update
        } catch (SQLException e) {
            e.printStackTrace(); // Print stack trace if SQL operation fails
        }
    }

    // Method to retrieve all inventory items
    public List<InventoryItem> getAllItems() {
        List<InventoryItem> items = new ArrayList<>(); // List to store retrieved items
        String query = "SELECT * FROM inventory"; // SQL query to select all items
        try (Statement stmt = connection.createStatement();
             ResultSet rs = stmt.executeQuery(query)) { // Execute the query
            while (rs.next()) { // Iterate through the result set
                InventoryItem item = new InventoryItem(
                        rs.getInt("id"), // Retrieve id
                        rs.getString("name"), // Retrieve name
                        rs.getInt("quantity"), // Retrieve quantity
                        rs.getDouble("price") // Retrieve price
                );
                items.add(item); // Add item to the list
            }
        } catch (SQLException e) {
            e.printStackTrace(); // Print stack trace if SQL operation fails
        }
        return items; // Return the list of items
    }

    // Method to update an existing inventory item
    public void updateItem(InventoryItem item) {
        String query = "UPDATE inventory SET name = ?, quantity = ?, price = ? WHERE id = ?"; // SQL query to update item
        try (PreparedStatement stmt = connection.prepareStatement(query)) {
            stmt.setString(1, item.getName()); // Set updated name
            stmt.setInt(2, item.getQuantity()); // Set updated quantity
            stmt.setDouble(3, item.getPrice()); // Set updated price
            stmt.setInt(4, item.getId()); // Set item id to update
            stmt.executeUpdate(); // Execute the update
        } catch (SQLException e) {
            e.printStackTrace(); // Print stack trace if SQL operation fails
        }
    }

    // Method to delete an inventory item by id
    public void deleteItem(int id) {
        String query = "DELETE FROM inventory WHERE id = ?"; // SQL query to delete item
        try (PreparedStatement stmt = connection.prepareStatement(query)) {
            stmt.setInt(1, id); // Set id of item to delete
            stmt.executeUpdate(); // Execute the update
        } catch (SQLException e) {
            e.printStackTrace(); // Print stack trace if SQL operation fails
        }
    }
}