Lecture 12 - Structures

Lecture 12 – Structures

Outline “

Last lecture, we discussed Enumerations… “

Which allow us to place limits on our primitive data types… “

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We also took a brief look at Objects, “

which combine: “ “

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Via the Enum Keyword.

Attributes (via Members and Properties) Behaviors (via Methods)… z to form a complex data type,

With a closer look at the special (unique) object we’ve been using: Form1.

In this Lecture, we introduce Structures: “

Which allow us to combine several primitive Data Types. “

Into a single, newly-defined Type.

Introduction “

With Structures, we may combine… “

Public members, methods, and properties “

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Note that members may be of different data types…

Private members and methods.

Although similar to Classes, Structures are a bit different: “

First of all, they use a different method of instantiation… “

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Objects are reference types: “ “

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i.e., creation of an instance. To instantiate (make) a new instance , the New keyword is required. For instance: Form1 is made for us, automatically.

Structures, on the other hand, are value types: “

To make a new Structure instance, New is not required. z

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Ex: We can use the Dim keyword to declare an instance...

This is just like primitive data types (Integer, Double, etc).

Structures and Classes may be built in a similar manner… “

Via a separate Class file (*.vb)...

Building a Structure “

Structures are often defined separately from the GUI (Form1): “

In a separate Class File ( e.g., Customer.vb). “ “

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However, a Structure could instead be defined at the top of Form1. “

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Much as we defined our DayAction Enumeration, last time.

Note: We could also have defined our DayAction… “

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This is to enhance clarity, reusability, and portability. We will do this, today.

In its own DayAction.vb file (note the matching name).

To define a VB Structure, we use the syntax: Structure Member declarations, properties, and methods

End Structure “

After defining our Structure, we may declare a new instance… “

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Via the Dim keyword, or alternately as a Member of Form1.

We will now discuss this more clearly, by example…

At this point, Open Visual Studio .NET… “

And create a new Windows Application , called ‘Structure Demo’.

Example: The Customer Structure

Example (Cont):

three

Example (Cont):

Example (Cont):

Adding Properties to Structures “

Like Classes, Structures are defined to have ‘Members’ … “ “

These express structure characteristics (may be Public or Private) In our last example, we accessed Structure Members directly… “

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Via the dot ( . ) operator, on a one-to-one basis…without abstraction.

However, Members may be handled indirectly via Properties. “

These ABSTRACT-AWAY Member details. “

We saw this for Classes, last Lecture.

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We may also define Properties for Structures.

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Public Property prop_Name() As Get_DataType Get ‘method to return the value of Property Statements … End Get Set ‘method to set the value of Property Statements … End Set End Property The Get and Set methods are both accessed via the DOT OPERATOR.

Example: Adding Properties