extensions.Therefore, using managed extensions, the existing code can be reused, saving both time and effort. You can also use managed extensions to merge both unmanaged and managed C++ code in an application.

Attributes that enable you to extend the functionality of a language and simplify the creation of COM components are supported by Visual C++ .NET. You can also apply classes, data members, or member functions to attributes.

Overview of Visual Basic .NET

The complete framework of Visual Basic .NET is based on the .NET Framework. Visual Basic .NET inherits the various features of the .NET Framework along with features of the earlier versions of Visual Basic. In this section, you will learn about the features of Visual Basic .NET as compared to the features in the earlier versions of Visual Basic.

As discussed earlier, Visual Basic .NET supports implementation inheritance as compared to the earlier versions of Visual Basic that supported interface inheritance. In other words, you can implement only interfaces with the earlier versions of Visual Basic. All the methods of the interface need to be implemented when you implement an interface in Visual Basic 6.0. In addition, the code has to be rewritten each time you implement the interface.

Visual Basic .NET, on the other hand, supports implementation inheritance.This implies that while applications are created in Visual Basic .NET, a class can also be derived from another class, which is known as the base class. The methods and properties of the base class are inherited by the derived class. In the derived class, you can either use or override the code that already exists in the base class.Therefore, code can be reused with the help of implementation inheritance. Although multiple interfaces can be implemented in a class in Visual Basic .NET, the class can inherit from only one class.

Visual Basic .NET also provides constructors and procedures, where constructors are used to initialize objects. The Sub New procedure replaces the Class_Initialize event in Visual Basic .NET. The Sub New procedure is executed when an object of the class is created, unlike the Class_Initialize event that is available in the earlier versions of Visual Basic.The first procedure to be executed in a class is the Sub New procedure. Instead of the Class_Terminate event, the Sub Finalize procedure is available in Visual Basic .NET. When an object is destroyed, the Sub

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Finalize procedure is automatically called to complete the tasks that remain incomplete. In addition, the Sub Finalize procedure can only be called from the class to which it belongs or from the classes from which it is derived.

Visual Basic .NET has another additional feature known as garbage collection. Allocated resources such as objects and variables are monitored by the .NET Framework. In addition, the destroying objects, which are no longer in use, automatically release memory for reusing the objects in the .NET Framework. When an object is set to Nothing, in Visual Basic 6.0, it is destroyed automatically, whereas in Visual Basic .NET, it continues to occupy space even when it is set to Nothing. In Visual Basic .NET, the garbage collector checks the objects that are not currently used by the applications.The garbage collector releases the memory occupied by the object when any object is found marked for garbage collection.

The GC class, the Sub Finalize procedure, and the IDisposable interface are used to perform garbage selection operations in the .NET Framework. The System namespace contains the GC class that provides various methods that enable you to control the system garbage collector. In the .NET Framework, a member of the Object class, the Sub Finalize procedure, acts as a destructor. You can also override this procedure in your applications. However, the Sub Finalize procedure is not executed when the application is executed. The Sub Finalize procedure is called by the GC class to release the memory that is occupied by a destroyed object. However, an explicit way of managing resources in the form of the IDisposable interface is provided by the .NET Framework.The Dispose() method is included in the IDisposable interface. After the IDisposable interface is implemented, the Dispose() method can be overridden in the applications. You can release resources and database connections in the Dispose() method.

Overloading is a feature that enables you to define several procedures with the same name, where each procedure has a different set of arguments. Visual Basic

.NET supports this feature of overloading as compared to the earlier versions of Visual Basic. You can use overloading for constructors and properties in a class along with the procedures. The Overloads keyword is used for overloading procedures.

Consider a scenario in which a procedure needs to be created to display the address of an employee. The address of the employee should be viewed based on either the employee name or the employee code, which can be done by using the overload feature. You need to create two procedures with the same name but

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Visual Basic .NET enables you to detect and remove errors at run time by supporting structured exception handling. In Visual Basic .NET, you can use Try…Catch…Finally statements to create exception handlers. By using Try…Catch…Finally statements, you can create strong and efficient exception handlers to improve the performance of the application.

You have considered the new and added features of Visual Basic .NET. The following sections discuss the features of an object-oriented programming language.

Features of an Object-Oriented

Programming Language

In an object-oriented programming language, objects serve as the building blocks of a programming language, displaying a unique identity and behavior. A chair, a table, and a book are examples of objects that are used every day. An object in a programming language is defined as an instance of a class. Applications created in an object-oriented programming language are made up of objects.

An object is qualified as an object-oriented programming language if the following features are supported:

Abstraction

Encapsulation

Inheritance

Polymorphism

The next sections will consider each of the features mentioned here in detail.

Abstraction

Before you buy a television set, you consider its size, durability, and features. As a buyer, you may not be interested in knowing about the machinery of the television set.The main features of the television set are more likely to be your primary concern. This is known as abstraction. In a programming language, abstraction helps you focus mainly on the essential aspects of an object. The nonessential aspects are normally overlooked.