Interfaces werethe most important feature introduced in VB 5, but are still one of the leastunderstood or used.Īs you'll see later in this chapter, VB.NET has improved support forinterfaces.
Interfaces provide early binding to an object, which can greatly improveperformance and also provide type protection at compile time. A variablethat instantiates an interface can reference any class that implements thatinterface. Any number of classes can implement the same interface. An interface defines a set of properties, methods, and events that a classimplements. VB 5 introduced an additional form of polymorphism using interfaces. Type safety also is onemechanism to prevent hackers from overloading code with a destructive piece ofcode. Type safety is the concept to ensure that a string is used as astring, an integer is used as an integer, and a Boolean is used as a Boolean.Without type safety, potentially more errors can occur when a user is executinga program rather than when the program is compiled. This worked, but did not provide any type safety at compiletime. Given two different classes with the same properties and methods, avariable of type object could be used to instantiate an objectof either class. Late binding is the technology for codeto determine at runtime what properties and methods a given object provides.This allows code to create any object and attempt to call a method or propertyof that object without knowing whether the object supports the method at compiletime. Visual Basic introduced a very limited support for polymorphism in VB 4.0through the use of late binding. Polymorphism sounds a great deal like encapsulation, but it is different.Encapsulation has to do with hiding the internal implementation of an object.Polymorphism has to do with multiple classes having the same interface.
They are bothcars that is, they both derive from the Car class, andthey both have a drive method, but the implementations ofthe methods could be drastically different. For example, consider two objects,one representing a Porsche 911 and the other a Toyota Corolla. Polymorphism is the concept that different objects have differentimplementations of the same characteristic. Visual Basic 2015 in 24 Hours, Sams Teach Yourself
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