In visual basic, Interface is same as a class but the only difference is class can contain both declarations and implementation of methods, properties, and events but Interface will contain only the declarations of methods, properties, and events that a class or structure can implement.
The Interface in visual basic is more like a contract and the class or structure that implements an interface must provide the implementation for all the members that are specified in the interface definition.
Generally, visual basic will not support multiple inheritance of classes but that can be achieved by using Interface. In addition, a structure in c# cannot be inherited from another structure or class but that can be inherited by using interfaces.
In visual basic, we can define the interface by using Interface keyword. Following is the example of defining the interface using Interface keyword.
Interface IUser
Sub GetDetails()
End Interface
If you observe the above code snippet, we defined an interface (IUser) using Interface keyword with GetDetails method signature. Now, the IUser interface can be implemented by any class or structure by providing a definition for the GetDetails method.
To implement an interface in a class or structure, the syntax will be like as shown below.
Class User
Inherits IUser
Private Sub GetDetails() Implements IUser.GetDetails
' Method Implementation
End Sub
End Class
If you observe the above code snippet, we inherited an interface (IUser) in a class (User) and implemented a defined interface method in the class.
In visual basic, the interface cannot be instantiated directly but, it can be instantiated by a class or structure that implements an interface. Following is the example of creating an instance for the interface in a visual basic programming language.
Dim u As IUser = New User()
In visual basic, a class can inherit only from one class but we can implement multiple interfaces in a class or structure by using interfaces.
By default, the members of interface are public and we are not allowed to include any other access modifiers. In visual basic, an interface can contain methods, properties, events, indexers but it can’t contain constants, fields, operators, instance constructors, finalizers or types.
Following is the example of creating and implementing an instance using a class in a visual basic programming language.
Module Module1
Interface IUser
Sub GetDetails(ByVal x As String)
End Interface
Class User
Implements IUser
Public Sub GetDetails(ByVal a As String) Implements IUser.GetDetails
Console.WriteLine("Name: {0}", a)
End Sub
End Class
Class User1
Implements IUser
Public Sub GetDetails(ByVal a As String) Implements IUser.GetDetails
Console.WriteLine("Location: {0}", a)
End Sub
End Class
Sub Main(ByVal args As String())
Dim u As IUser = New User()
u.GetDetails("Suresh Dasari")
Dim u1 As IUser = New User1()
u1.GetDetails("Hyderabad")
Console.WriteLine("Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created an interface IUser, two classes “User & User1” and implemented an interface IUser by providing an implementation for GetDetails() method. Here, we created an instance for interface “IUser” using User & User1 classes.
When we execute the above visual basic program, we will get the result as shown below.
As discussed, visual basic will not support multiple inheritance of classes but that can be achieved by using the interface.
Following is the example of implementing a multiple inheritance using interfaces in a visual basic programming language.
Module Module1
Interface IName
Sub GetName(ByVal x As String)
End Interface
Interface ILocation
Sub GetLocation(ByVal x As String)
End Interface
Interface IAge
Sub GetAge(ByVal x As Integer)
End Interface
Class User
Implements IName, ILocation, IAge
Public Sub GetName(ByVal a As String) Implements IName.GetName
Console.WriteLine("Name: {0}", a)
End Sub
Public Sub GetLocation(ByVal a As String) Implements ILocation.GetLocation
Console.WriteLine("Location: {0}", a)
End Sub
Public Sub GetAge(ByVal a As Integer) Implements IAge.GetAge
Console.WriteLine("Age: {0}", a)
End Sub
End Class
Sub Main(ByVal args As String())
Dim u As User = New User()
u.GetName("Suresh Dasari")
u.GetLocation("Hyderabad")
u.GetAge(32)
Console.WriteLine(vbLf & "Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created multiple interfaces and implemented those interfaces using the User class to achieve multiple inheritance.
When we execute the above visual basic program, we will get the result as shown below.
This is how we can achieve multiple inheritance using the interface in a visual basic programming language.
The following are the important features of the interface in a visual basic programming language.