C# difference between casting and as?

Question

Possible Duplicate:
What is the difference between the following casts in c#?

In C#, is a there difference between casting an object or using the as keyword? Hopefully this code will illustrate what I mean...

String text = "Hello hello";
Object obj = text; 

String originalCast = ((String)obj).ToUpper();
String originalAs = (obj as String).ToUpper();

Thanks

:)

Answer 1

as will never throw a InvalidCastException. Instead, it returns null if the cast fails (which will give you a NullReferenceException in your example).

Answer 2

Using 'as' will not throw an exception if the obj is not a String. Instead it'll return null. Which in your case will still throw an exception since you're immediately referencing this null value.

Answer 3

As far as I know!

Using 'as' will return null if the 'cast' fails where casting will throw an exception if the cast fails.

Answer 4

Other than InvalidCastException that's already mentioned...

as will not work if the target type is a value type (unless it's nullable):

obj as int // compile time error.