C#

public class GCommon<T> : Collection<T> where T : ICommonInterface
   {

       new public void  Add(T item)
       {
           if(!base.Contains(item))
               base.Add(item);

       }
       public void Clear(T item)
       {
           foreach (T it in base.Items)
           {
               if(it.Equals(item))
                   base.Remove(item);
           }
       }
       new public bool Contains(T item)
       {
           bool retval = false;
           foreach (T itm in base.Items)
               if (itm.Equals(item))
               {
                   retval = true;
                   break;
               }
           return retval;
       }


   }

   public interface ICommonInterface
   {
   }


   public class clsContent : ICommonInterface
   {
       public clsContent()
       {

       }

       public clsContent(int id,string Name, string Content)
       {
           _Id = id;
           _ContentName = Name;
           _Content = Content;
       }

       private int _Id;
       public int Id
       {
           get { return _Id; }
           set { _Id = value; }
       }

       private string _ContentName;
       public string ContentName
       {
           get { return _ContentName; }
           set { _ContentName = value; }
       }

       private string _Content;
       public string Content
       {
           get { return _Content; }
           set { _Content = value; }
       }

   }