What is the best way to save the result of an inner join and call the results by a method

I have two inventory and product tables, in product I have some data and in other inventory, they are linked by the product number. In my code I have two objects that have the columns of each table as attributes. Until there nothing new.

Generally, when I consult a table of a single type of objects, I save the results in an ArrayList of the object type (product, inventory, etc). The issue is that I will make a query that shows me data of both tables with a join, but I do not know how to save the results. In summary would be a multidimensional list that is the first time I perform.

Someone who takes pity on me !!!! PS I think I have no problems with the query because it pulls .. My Product object

public class Producto implements Serializable {
private int Num_Producto;
private String NombreProd;
private String Clasificacion;
private float Precio_Venta;
private float Precio_Compra;

My Inventory Object

public class Inventario implements Serializable {
private int Num_Inventario;
private int Producto_Num;
private int Cantidad;
private int EmpleadoSrv;
private String FechaCad;
private String Lote;

My method attempt

public static ArrayList ***no se como va ****ConsultarProductobyInventario() {
       PreparedStatement st = null;        
    try {
        String SQL = "SELECT producto.NombreProd, producto.Clasificacion, producto.Precio_Venta, inventario.Cantidad, inventario.Lote FROM producto join inventario on  inventario.Producto_Num = producto.Num_Producto;";
        st= conexion().prepareStatement(SQL);
        ResultSet res = st.executeQuery();
        ArrayList<Producto> lista = new ArrayList<>();
        Producto prod;
        while(res.next()){ //aqui menos!!!!
            prod=new Producto();
            prod.setNum_Producto(res.getInt("num_producto"));
            prod.setNombreProd(res.getString("nombreprod"));
            prod.setClasificacion(res.getString("clasificacion"));
            prod.setPrecio_Venta(res.getInt("precio_venta"));
            prod.setPrecio_Compra(res.getInt("precio_compra"));

            lista.add(prod);
        }
        //st.close();
        return lista;
    } catch (SQLException ex){
        Logger.getLogger(EmpresaDAO.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;

}