Question

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Direct casting vs 'as' operator?

Anyone can give a comparison between as and cast?

Answer 1

A straight cast will fail if the object being casted is not of the type requested. An as-cast will instead return null. For example:

object obj = new object();
string str = (string)obj; // Throws ClassCastException

However:

object obj = new object();
string str = obj as string; // Sets str to null

When the object being casted is of the type you are casting to, the result is the same for either syntax: the object is successfully casted.

Note specifically that you should avoid the “as-and-invoke” pattern:

(something as SomeType).Foo();

Because if the cast fails, you will throw a NullReferenceException instead of a ClassCastException. This may cause you to chase down the reason that something is null, when it’s actually not! The uglier, but better code

((SomeType)something).Foo();

Will throw a ClassCastException when the object referenced by something cannot be converted to SomeType, and a NullReferenceException when something is null.