The VB.NET language is disarmingly simple, with relatively few keywords and a dozen built-in datatypes, but VB.NET is highly expressive when it comes to implementing modern programming concepts. VB.NET includes all the support for structured, component-based, object-oriented programming that one expects of a modern language.
At the heart of any object-oriented language is its support for defining and working with classes. Classes define new types, allowing you to extend the language to better model the problem you are trying to solve. VB.NET contains keywords for declaring new classes and their methods and properties, and for implementing encapsulation, inheritance, and polymorphism, the three pillars of object-oriented programming.
VB.NET also supports interfaces, a means of making a contract with a class for services that the interface stipulates. In VB.NET, a class can inherit from only a single parent, but a class can implement multiple interfaces. When it implements an interface, a VB.NET class in effect promises to provide the functionality the interface specifies.
VB.NET also provides support for structures. A structure is a restricted, lightweight type that, when instantiated, makes fewer demands on the operating system and on memory than a conventional class does. A structure can't inherit from a class or be inherited from, but a structure can implement an interface.
VB.NET provides component-oriented features, such as properties, events, and declarative constructs (called attributes). Component-oriented programming is supported by the CLR's support for storing metadata with the code for the class. The metadata describes the class, including its methods and properties, as well as its security needs and other attributes, such as whether it can be serialized; the code contains the logic necessary to carry out its functions. A compiled class is thus a self-contained unit; therefore, a hosting environment that knows how to read a class' metadata and code needs no other information to make use of it. Using VB.NET and the CLR, it is possible to add custom metadata to a class by creating custom attributes. Likewise, it is possible to read class metadata using CLR types that support reflection.
An assembly is a collection of files that appear to the programmer to be a single dynamic link library (DLL) or executable (EXE). In .NET, an assembly is the basic unit of reuse, versioning, security, and deployment. The CLR provides a number of classes for manipulating assemblies.
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