working with objects
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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 This is normally what we want to know
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 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 variables1. 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. Name of the variable2. Type of the variable (What kind of variable you have)
String StringBuilder TextBox
TypeName
Declaring Object Variables – 2
Use a name that is easy to remember. Do not use x, y, z
Begin each separate word in a name with a capital letter Examples
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
New Keyword Type of Object
Sometimes extra data is required
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
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()
MethodInput Output
Method Inputs - 2
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.
MethodInput Output
Click on link to get more informationMethod Name
Parameters
Method Outputs
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
MethodInput Output
OutputInformation
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 can find a list of constructors in the MSDN Documentation.
You can also find a list of constructors using the IntelliSense capability.
Dim x as StringBuilder = new StringBuilder
Dim y as StringBuilder = new StringBuilder(“hello”)Dim z as StringBuilder = new StringBuilder(6)
You don’t need parenthesisif you are not passing parameters
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.