Problemas com alterar...... urgente

import java.sql.*;
public class CadAlterar {
    
   public static String sql;
       
	public static PreparedStatement stmt;
        public static ResultSet res = null;
        
        
	public static void altera(Fornecedor f){
             try{
		// conecta no banco
		ConnectionFactory.conecta();
                sql = "UPDATE fornecedores set  cod_fornecedor=?, nome=?, razao_social=?, endereco=?, cidade=?, estado=?, cnpj=?, ie=?, e_mail=?, site=?, telefone=?, fax=?" ;
                stmt=ConnectionFactory.con.prepareStatement(sql);
                        stmt.setInt(1, f.getCod_fornecedor());
                        stmt.setString(2, f.getNome());         
                        stmt.setString(3,f.getRazao_social());
                        stmt.setString(4,f.getEndereco());
                        stmt.setString(5,f.getCidade());
                        stmt.setString(6,f.getEstado());
                        stmt.setString(7,f.getCnpj());
                        stmt.setString(8,f.getIe());
                        stmt.setString(9,f.getE_mail());
                        stmt.setString(10,f.getSite());
                        stmt.setString(11,f.getTelefone());
                        stmt.setString(12,f.getFax());
                        stmt.executeUpdate();
                       
                }
        
         catch(SQLException e){
            System.out.println("SQLException: "+e.getMessage());
             } finally{
            ConnectionFactory.desconecta();                
            }
        }
        }