how httpwebrequest.getrequeststream return instance of abstract class system.io.stream

Question

System.io.stream is a abstract class then how httpwebrequest.getrequeststream() return the instance of stream class. i.e

 Stream serverStream  = request.GetRequestStream();

How stream class is initialized?

score 0 · Answer 1 · answered May 30 '15 at 07:21

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httpwebrequest.getrequeststream() returns one of the concrete classes that inherit from the abstract class System.IO.Stream.

answered May 30 '15 at 07:21

potatopeelings

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"The GetRequestStream method initiates a request to send data to the Internet resource and returns a Stream instance for sending data to the Internet resource." this is what msdn says and its seems not returning the concrete inherited class like file stream or memory stream – user1075564 May 30 '15 at 07:26
Do a Debug.WriteLine of serverStream.GetType().FullName and you'll get the actual concrete class. MSDN indicates that it could be any of the concrete classes inherited from Stream (an instance of x mostly means x and any class which can fill in for x) – potatopeelings May 30 '15 at 07:36

score 0 · Answer 2 · edited May 23 '17 at 12:23

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Stream is the abstract base class of all streams.

The Stream class and its derived classes provide a generic view of these different types of input and output, and isolate the programmer from the specific details of the operating system and the underlying devices.

and

httpwebrequest.getrequeststream

Gets a Stream object to use to write request data.

You have to create an instance of stream subclasses to get initialized.

go through this and this SO post for more .

edited May 23 '17 at 12:23

Community

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answered May 30 '15 at 07:26

Tharif

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The code in question is working code and i am not looking for initializing the stream class using subclass. my question is how the above code is initializing the abstract class – user1075564 May 30 '15 at 07:30
nope i had not created a instance i can't create a instance of stream class as its an abstract class using the new operator. so just wondering how this statement "Stream serverStream = request.GetRequestStream();" is initializing the stream class – user1075564 May 30 '15 at 07:37

score 0 · Answer 3 · answered May 30 '15 at 07:45

You are confusing the type of a reference with the type of an object.

The fact that a method signature declares a particular type as its return type does not mean that instances returned will be of that exact type, they could be of a type derived from the one specified, as in you case.

Try this: Console.WriteLine(stream.GetType()), should clear your thoughts a bit.

how httpwebrequest.getrequeststream return instance of abstract class system.io.stream

3 Answers3