Site Column creating via code

Site columns can be created while site provisioning and later these field can be attached to content type and associating this content type to a specific list. Place below code in "Feature Receiver".

 public string _firstNameText = "";
        public string _secondNameText = "";    

        public override void FeatureActivated(SPFeatureReceiverProperties properties)
        {
            
            using (SPSite site = (SPSite)properties.Feature.Parent)
            {
                using (SPWeb web = site.OpenWeb())
                {
                    web.Fields.AddFieldAsXml(_firstNameText);
                    web.Fields.AddFieldAsXml(_secondNameText);
                    
                    web.Update();
                }
            }

        }