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Posted on 2003-10-26
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How come some methods like: .ToLower() don't require a namespace but one such as: .WriteLine() does?
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Question by:chilled2003
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Expert Comment

by:smitty22
ID: 9623918
ToLower operates on string objects, while WriteLine is a static method that is part of the Console class.  The full specification of WriteLine is
  System.Console.WriteLine().
This is because Console is a member of the System namespace.  However, since System is usually always included as a using directive, you can just write Console.WriteLine().

String is also part of the System namespace, but the ToLower method is not static -- in other words, it operates on instantiated members of the String class.  This is why you can do things like
  string s = "Hello";
  s.ToLower();
--BUT NOT--
  String.ToLower();


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Expert Comment

by:kellycoinguy
ID: 9623928

String.ToLower is in System.String
Console.WriteLine is in System.Console
both in the System namespace.

I believe if you put:
using System;

at the top of your file, you shouldn't need to specify a namespace just the object:

Console.Writeline("..."); // this works fine for me

Can you be more specific about what you are required to do here?

-Kelly
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Author Comment

by:chilled2003
ID: 9624228
Not really required to do anything just trying to learn C# :)  If .ToLower(); is in the System namespace then how come I cant put:

System.String.ToLower();
or
String.ToLower();

If it's part of System then how come if I dont include System as a namespace it still works with just .ToLower(); ?  But if I do that with WriteLine(); it errors and I have to put System.Console.WriteLine();
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Accepted Solution

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smitty22 earned 200 total points
ID: 9624354
.ToLower belongs to the String class, which in turn belongs to the System namespace.  You can use string methods without a "using System;" directive because they are an exception -- they are handled almost like a primitive type such as int or double.  The "using System;" directive is implied when working with strings as primitive types.

For instance, without a using System directive you can do:
  string str = "this is a string";  // note lowercase "string"
  System.Console.WriteLine( str.ToLower() );  // or any other string method
BUT NOT
  String s = new String("this is not valid");  // compiler error: "missing a using directive"
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Author Comment

by:chilled2003
ID: 9624368
Thanks, that cleared it up for me :)
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