Interface in VB .Net

Introduction

• Interfaces are a core OOP concept in VB.NET that enable polymorphism, multiple inheritance, and clean architecture.

Definition

• An interface in VB.NET is a programming construct that defines a set of methods, properties, and event declarations without providing their implementation.
• An interface in VB.NET is a blueprint that defines method signatures without implementation, which must be implemented by any class that uses it.

Characteristics

• It acts as a contract that specifies what operations a class must perform, but not how those operations are carried out.
• An interface specifies what to do, not how to do.
• An interface is used to achieve multiple inheritance because a class in VB.NET can implement more than one interface, even though it can inherit from only one class.
• Any class or structure that implements an interface is compulsorily required to implement all the members declared in that interface. Simply, an interface in VB.NET defines a set of members that a class must implement.
• Interfaces help in achieving polymorphism because an interface reference can point to objects of different classes that implement the same interface.
• Interfaces are mainly used to define standard behavior that multiple unrelated classes can follow.
• They also promote loose coupling, making programs easier to maintain, modify, and extend.

Rules of Interface in VB.NET

• Interface members are Public by default.
• In Interface, no method body is allowed.
• Interface has no constructors.
• An Interface cannot contain fields, method bodies, or instance variables.
• An Interface can contain Methods, Properties, and Events.
• A class can implement multiple interfaces.

Syntax

Example

Use of Interface in VB.NET

An Interface is mainly used –

• To achieve multiple inheritance.
• To enforce standard behavior.
• To support loose coupling.
• To implement runtime polymorphism.
• To improve maintainability and testability.

Advantages of Interface

• They promote standardization.
• They enhance code reusability.
• They support dependency injection.
• They make code flexible and scalable.

Limitations of the Interface

• It has no implementation code.
• It does all the members must be implemented.
• It is more complex for beginners.

Use/Applications

The concept of an Interface is used in our real-world life are –

• As a USB interface
• As a printer interface
• As a connectivity with a database provider interface

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Example : Interface Examples in VB .Net program to demonstrate the Interface. 

Module Module1
    Interface Program1
        Sub Output()
    End Interface

    Class Example
        Implements Program1
        Sub Output() Implements Program1.Output
            ' Method Implementation
            Console.WriteLine("Interface Executed")
        End Sub
    End Class

    Sub Main()
        Dim Obj As New Example()
        Obj.Output()
    End Sub
End Module

Output:
Interface Executed

Example : Interface Examples in VB .Net program to demonstrate Multiple Inheritance using an Interface. 

Module Module1
    Interface A
        Sub Display1()
    End Interface

    Interface B
        Sub Display2()
    End Interface

    Interface C
        Sub Display3()
    End Interface

    Class Example
        Implements A, B, C

        Sub Display1() Implements A.Display1
            Console.WriteLine("Display1() Function Executed")
        End Sub

        Sub Display2() Implements B.Display2
            Console.WriteLine("Display2() Function Executed")
        End Sub

        Sub Display3() Implements C.Display3
            Console.WriteLine("Display3() Function Executed")
        End Sub
    End Class

    Sub Main()
        Dim Obj As New Example()
        Obj.Display1()
        Obj.Display2()
        Obj.Display3()
    End Sub
End Module

Output:
Display1() Function Executed
Display2() Function Executed
Display3() Function Executed