Calling a Method in C#

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Calling a Method
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In Listing 42, the namespace for the Console type is System The System namespace contains the types that enable the programmer to perform many fundamental programming activities Virtually all C# programs use types within the System namespace Table 41 provides a listing of other common namespaces
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TABLE 41: Common Namespaces
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Namespace
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System
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Description Contains the definition of fundamental types, conversion between types, mathematics, program invocation, and environment management Includes types for working with collections of objects Collections can generally follow either list or dictionary type storage mechanisms This C# 20 added namespace works with strongly typed collections that depend on generics (type parameters) Contains types used for working with data that is stored within a database Contains types for drawing to the display device and working with images Contains types for working with files and directories and provides capabilities for manipulating, loading, and saving files Provides classes and interfaces for querying data in collections using a C# 30 added API, Language-Integrated Query Includes types for working with strings and various text encodings, and for converting between those encodings This namespace includes a subnamespace called SystemTextRegularExpressions, which provides access to regular-expression-related APIs Handles thread manipulation and multithreaded programming
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Continues
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SystemCollections
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SystemCollectionsGenerics
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SystemData
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SystemDrawing
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SystemIO
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SystemLinq
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SystemText
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SystemThreading
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4: Methods and Parameters
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TABLE 41: Common Namespaces (Continued)
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SystemWeb
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Description A collection of types that enable browser-toserver communication, generally over HTTP The functionality within this namespace is used to support a NET technology called ASPNET Contains types that send and retrieve data over HTTP using the Simple Object Access Protocol (SOAP) Includes types for creating rich user interfaces and the components within them Contains standards-based support for XML processing
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SystemWebServices
SystemWindowsForms
SystemXml
It is not always necessary to provide the namespace when calling a method For example, if you call a method in the same namespace as the target method, then the compiler can infer the namespace to be the same as the caller s namespace Later in this chapter, you will see how the using directive avoids the need for a namespace qualifier as well
Type Name Calls to static methods ( 5 covers static versus instance methods) require the type name qualifier as long as the target method is not within the same class (such as a call from HelloWorldMain() to ConsoleWriteLine()) However, just as with the namespace, C# allows the elimination of the type name from a method call whenever the method is available on the containing type (Examples of method calls such as this appear in Listing 44) The type name is unnecessary because the compiler infers the type from the calling method If the compiler can make no such inference, the name must be provided as part of the method call At their core, types are a means of grouping together methods and their associated data For example, Console is the type name that contains the Write(), WriteLine(), and ReadLine() methods (among others) All of these methods are in the same group because they belong to the Console type
Calling a Method
Scope You already learned that scope bounds declaration and accessibility Scope also defines the inferred call context A method call between two methods in the same namespace does not require the namespace qualifier Similarly, two calls within the same class do not require the type name because the scope is the same Method Name After specifying which type contains the method you wish to call, it is time to identify the method itself C# always uses a period between the type name and the method name, and a pair of parentheses following the method name Between the parentheses may appear any parameters that the method requires Parameters All methods have from zero to n parameters, and each parameter in C# is of a specific data type For example, the following method call, used in Listing 42, has three parameters:
SystemConsoleWriteLine( "Your full name is {1} {0}",lastName, firstName)
The first is a string and the second two are of type object Although you pass parameter values of type string for the second two parameters as well, the compiler allows this because all types, including string, are compatible with the data type object
Method Return In contrast to SystemConsoleWriteLine(), SystemConsoleReadLine() in Listing 42 does not have any parameters However, this method happens to have a method return The method return is a means of transferring results from a called method back to the caller Because SystemConsoleReadLine() has a return, it is possible to assign the return value to the variable firstName In addition, it is possible to pass this method return as a parameter, as shown in Listing 43