Transcript Loops
Working With
Objects
Tonga Institute of Higher
Education
Introduction
Visual Basic .NET is an object-oriented language
The building block of an object-oriented
language is an object.
Object - A self-contained entity that contains data
and procedures to manipulate the data.
An object is like a tool that we can use to do
things.
You can find a list of pre-built objects in the
MSDN Documentation. (www.msdn.com)
Advantages of Object Oriented
Programming
Code is easier to maintain
Code is more readable
Encapsulation
Show what the object can do
Hide how the object does it
This can be very complicated
We often don’t care how it is done
Code is easier to reuse
This is normally what we want to know
A piece of code, once written, should not be thrown away. It
is best to reuse the code in other programs.
Example: Millions of people use MessageBox.Show(...).
But it was only written once.
Code development is more efficient
You don’t code the same thing over and over again
Objects
Objects are like variables with extra
functionality.
Look at MSDN documentation to find
functionality.
Examples:
String
String.Replace(…)
String.PadLeft(…)
TextBox
TextBox.Text(…)
TextBox.MaxLength(…)
Classes vs. Objects
Object - A self-contained entity that contains
data and procedures to manipulate the data.
Class - The blue print or design for creating an
object.
Instantiate – The act of creating an object from a
class
Instance – An instantiated class/object
Using Object Variables
2 Steps to using variables
1. Declare
the variable
2. Instantiate the variable / Initialize the variable
Declaring Object Variables – 1
Declare the variable – Tell the computer to reserve a space in
memory for the variable.
You need to tell the computer 2 things:
1.
2.
Name of the variable
Type of the variable (What kind of variable you have)
String
StringBuilder
TextBox
Name
Type
Declaring Object Variables – 2
Use a name that is easy to remember.
Begin each separate word in a name with a capital letter
Examples
Do not use x, y, z
FirstName
CustomerID
This works exactly the same for primitive variables!
Instantiating Object Variables /
Initializing Object Variables
Initialize the variable – Assign an initial value to a
variable
Instantiate – The act of creating an object from a class
Use the new keyword
Sometimes
extra data is
required
New Keyword
Type of Object
Declaring and Initializing Object
Variables in 1 line
You can declare and initialize a variable in 1 line.
Demonstration
Declaring, Instantiating and
Initializing Objects
Methods
Methods - Pieces of code that perform a single
function
Use
dot notation to access it
Example: <Object name>.<method name>(<parameters>)
You
can find a list of methods in the MSDN
Documentation.
You can also find a list of methods using the
IntelliSense capability.
Calling a Method – The act of using a method
Method Inputs - 1
Input
Method
Output
Some methods take inputs
Parameter/Arguments – A piece of information that
provides additional information to the method as to
how it should behave.
Parameters should be in the parenthesis next to the
method name
The order they are passed is important
Values are separated by commas
If you are not passing any parameters, you may or
may not use (). It is up to you.
Example: String.Trim
Example: String.Trim()
Method Inputs - 2
Input
Method
Output
Some methods take inputs
You can find a list of parameters in the MSDN
documentation.
You can find a list of parameters using the IntelliSense
capability.
Method Name
Click on link to get more information
Parameters
Method Outputs
Input
Method
Output
Some methods return outputs
When something is returned, it may or may not be used.
The programmer chooses what to do with the data returned.
Only one thing may be returned.
If something is coming back, we can see “As <object>” at the end of
the method in IntellliSense
If nothing is coming back, you will not see “As <object>” at the end of
a method in IntellliSense
Use popup windows while coding to see what is being returned
Output
Information
Functions vs. Subroutines
Subroutine – A method that does not
return anything
Function – A method that returns
something
Demonstration
Methods
Constructor
Constructor – A method that is automatically executed when an
object is created.
This allows you to set initial values for the object.
Many objects have multiple constructors. (They are overloaded)
You don’t need parenthesis
if you are not passing parameters
Dim x as StringBuilder = new StringBuilder
Dim y as StringBuilder = new StringBuilder(“hello”)
Dim z as StringBuilder = new StringBuilder(6)
You can find a list of constructors in the MSDN
Documentation.
You can also find a list of constructors using the
IntelliSense capability.
Demonstration
Constructors
Attributes / Fields / Properties
Attributes / Fields / Property – A variable that a
class allows others to see
Use dot notation to access it
Example: <Object name>.<field name>
You can find a list of attributes / fields /
properties in the MSDN Documentation.
You can also find a list of attributes / fields /
properties using the IntelliSense capability.
Demonstration
Attributes / Fields
Method Overloading
If two methods do the same thing, they should have the same name
Overloading - Having multiple methods with the same name but
different parameters
The correct method to use is determined by matching up the number
and type of arguments.
Therefore, you can’t have 2 methods with the same name and same
number & type of arguments.
Without overloading, we would have to remember more function
names. That would make code more complicated.
Demonstration
Overloaded methods
Members
Member – An attribute/field or method.
Sometimes used to refer to the both as a
whole.