Working With Objects

1. Working With Objects Tonga Institute of Higher Education

2. 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)

3. 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

4. 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(…)

5. 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

6. Using Object Variables • 2 Steps to using variables • Declare the variable • Instantiate the variable / Initialize the variable

7. 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: • Name of the variable • Type of the variable (What kind of variable you have) • String • StringBuilder • TextBox Type Name

8. 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!

9. 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

10. Declaring and Initializing Object Variables in 1 line • You can declare and initialize a variable in 1 line.

11. Demonstration Declaring, Instantiating and Initializing Objects

12. 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

13. Method Input Output 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()

14. Method Input 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. Click on link to get more information Method Name Parameters

15. Method Input Output 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 Output Information

16. Functions vs. Subroutines • Subroutine – A method that does not return anything • Function – A method that returns something

17. Demonstration Methods

18. 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. 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)

19. Demonstration Constructors

20. 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.

21. Demonstration Attributes / Fields

22. 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.

23. Demonstration Overloaded methods

24. Members • Member – An attribute/field or method. • Sometimes used to refer to the both as a whole.