application. When you create an application, some memory space is allocated to it.Therefore, all the variables, classes, objects,and other resources that you declare in the application are added to this memory space.This process is called heap allocation to an application. When you go on adding data to this heap, there comes a time when the memory allocated to your application becomes full and you cannot add more data to it. This is the time when the garbage collector becomes active.

The garbage collector scans the entire heap and deallocates memory to resources that are no longer in use, thereby creating free spaces in the heap. You can now add more objects to the memory.

Class Library

As discussed earlier, .NET provides you with several base classes. These base classes are available as a library of classes called the .NET base class library, which is an API similar to MFCs (Microsoft Foundation Classes) used with Visual C++ 6.0.

In addition to the base classes, the class library includes interfaces, value types, enumerations, and methods that allow you to perform a wide variety of tasks to make programming easier. Further, the classes contained in the .NET class library have a user-friendly name. This helps you to easily identify the classes that you need to use in your program. For example, if you need to create a thread, you use the Thread class. Similarly, to create an exception, you use the Exception class. You will learn about these classes later in this chapter.

A class library provides classes that help you create interoperable applications. This implies that the classes defined in the class library can be used to create a Visual C++ .NET, Visual Basic .NET, or C# application. In addition, the methods defined in the classes can also be used by any other .NET programming language.

Assembly

An assembly is a logical structure that contains complied code for the .NET Framework. An assembly can be stored in one file or multiple files and can be .dll or .exe files. You may also include files using COM objects, resource files, or metadata in an assembly. As discussed earlier, metadata stores information about managed code in .NET. Similarly, metadata in an assembly contains information about the assembly. Therefore, assemblies are self-describing.

Before developing applications for the .NET platform, programmers used to create applications by using DLLs. Assemblies offer you several advantages over .dll files. Assemblies contain types, resources, and metadata. Whatever resources you might require for your application, you can simply include them in the assembly. For example, you may include the namespaces containing the classes that you require for your application. This makes developing an application easier for you.

In addition, while working with assemblies, you need not worry about registering your assembly and managing and versioning of your application. Registering your application with the operating system is as simple as copying assembly files to your application directory.

Another important advantage of using assemblies is that they can be either shared or private. The following section will discuss shared and private assemblies in detail.

Private Assembly

As the name suggests, a private assembly is available only to the application for which you create it. When you create a private assembly, you need to provide the assembly along with the executable application. You create a private assembly when you do not need the assembly for another application. For example, if you create an assembly for a skills inventory system of the employees of an organization, you might not require the assembly for another application, such as the hardware inventory system of the organization.

Private assemblies offer you several advantages, such as:

Registering the assembly. You need not register your assembly. To use a private assembly, you only need to copy it to the directory or subdirectory of your application.

Securing the application. A private assembly makes your application safe to use because no other application can access the resources of the private assembly. This implies that no other application can make changes to the private assembly, giving the application full control over the assembly. You do not require security permissions for a private assembly, as these permissions are contained in the application’s directory.

12Part I INTRODUCTION TO C#

Applying naming conventions to the resources. Because the resources in the private assembly are only accessible to your application, you need not worry about the naming convention of these resources. Even if two namespaces in different private assemblies have the same name, it does not affect the performance of any of the application.

Shared Assembly

Consider a situation in which you need to create an application for different processes of the HR system, such as payroll generation, leave processing, and employee appraisal system. All these processes need to use the Employee class. In such a scenario, it is preferable to reuse the same class in all the listed systems instead of creating a class for each application. Therefore, you can create an assembly that you can use in multiple applications. Such an assembly is called a shared assembly. You can also use a shared assembly in all .NET languages if the assembly is created according to the CLS standards discussed earlier.

Multiple applications use shared assemblies; therefore, the assemblies cannot be stored with a specific application. Shared assemblies are stored in the assembly cache, which is a special directory in the file system. To store a shared assembly in the assembly cache, you can use .NET utilities, such as Gacutil.exe and Regasm.exe.

Working with shared assemblies is not as simple as working with private assemblies. Because the resources in the shared assembly can be accessed across applications, you need to be careful with the versioning and naming convention of these resources. Shared assemblies are given a strong name, which is a unique name that applications need to specify to access the shared assembly. However, versioning problems can be solved by accessing the resources with the correct version number.

The following features make assembly an important component of .NET applications:

Self-describing

Side-by-side

Version dependency

Application domain

Zero-impact installation

These features are discussed in detail in the following subsections.