Using Structures in VB.NET
Structures are complex data types that encapsulate small pieces of tightly related data items. As with
Structures can contain data members as well as member methods to work with data inside a structure. Since the in-memory representation of
Structure is ‘value type’, memory management is handled efficiently.
Structures Vs Classes
|Value type||Reference type|
|Supports data members, code members (methods) and events||Supports data members, code members (methods) and events|
|Can not inherit||Supports inheritance|
|Preferable when you perform large number of operations on each instance||Preferable when you need to initialize one or more members upon creation|
|Can not control initialization using structure variable||Can have parameterized constructors|
|Less flexible, limited event handling support||More flexible, unlimited event handling support|
Structures are declared using
End Structure statements. Between these two statements, there must be at least one member declared. This member can be of any data type, non-shared and non-event. The following example shows how to encapsulate product info into a structure called
Private Structure Product 'Declare data members Public ProductID as Integer Public ProductName as String Private UnitPrice as Single 'Declare code members Public Function GetPrice() as Single GetPrice = UnitPrice End Function End Structure
In the above example, the
Product structure is declared as
Private. That means you can not access it from the object of the class where you defined it. As you can see, the data member
UnitPrice is declared as
Private, yes, you are right, you can’t access it outside the structure.
Note that there is a function
GetPrice defined within the
Structure. Using this code member, one can get
UnitPrice of a product. You can also define
Sub procedures, properties and events. You can define a property as a default property, but it must accept at least one argument. You can declare events using
Shared Sub procedure. To cause an event to actually happen, you have to use
The default accessibility for a structure is
Public. You can use
Friend keywords also. You must specify accessibility for every member you declare inside a
Structure. If you declare them with
Dim statement, they are considered as
Public. Remember that you can not initialize a
Structure‘s data members at the time of instantiation. You have to access and initialize them individually after creation of a
Structure variable or through a
Structure code member. If you assign one
Structure variable to another, a new copy is created in the other variable. Hence the changes to the values of first variable does not happen to the second. On the other hand, if you assign a
Class object to another, changes to the data of one object reflects in the other. This is obvious in the case of
Classes because the two objects in the above situation share the same instance.
Structures only if you want to use tiny pieces of related data as a single composite data type that resembles a built-in data type.
Classes if you can’t decide which one to use among
Classes are more flexible. Though there are storage and performance advantages with
Structures, often they are negligible.