Which is the proper way to cast?

Question

I have this interface:

public interface IEntity
{
    int Id{get;set;}
}

A class:

public class Customer: IEntity
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

and this is my usage:

void Main()
{
    List<Customer> list =  new List<Customer>();
    IEntity obj = null;
    obj = new Customer() {Id = 4, Name="Jenny", Age =41};
    list.Add(obj as Customer);  /*Line #1*/     
    list.Add((Customer)obj); /*Line #2*/        
}

Which is considered best practice: Line #1 or Line #2?

Answer 1

The () cast operator will throw an exception (InvalidCastException) if the source cannot be cast to the target type. The as operator will set the resulting variable to null if the cast cannot be completed.