Object-Oriented Programming - C Sharp Programming - Lecture Slides, Slides of C programming

Download Object-Oriented Programming - C Sharp Programming - Lecture Slides and more Slides C programming in PDF only on Docsity! Object-Oriented Programming 07_classes.ppt Docsity.com Overview of Topics • Object-Oriented Programming (OOP) • Class vs Object • Unified Modeling Language (UML) • Defining Classes • Using Classes • Read-Only Properties • Instance vs. Static (Shared) • Constructors and Destructors Docsity.com Class Analogy • A class is like a blueprint of a house. • Each house being built allows for the selection of tile, carpet, and wall colors. • So on the order form their may be a blank line to enter the color chosen, much like a variable. • Each house built based on the blueprint is an instance of the house. • We can not move into a blueprint; a house must be built. Docsity.com Object Analogy • An actual house is the object. • The object has specific values, such as the colors chosen by the homeowner, but the class allows for color selection. • The homebuilder may offer various methods of applying the paint, such as roller, brush, or sponge. • If they don’t apply the paint, what’s the point in choosing colors. • Many houses may be built from the same blueprint. – Each will have its own plot of land. – Most will have different colors. – Some may have the same colors, but they will still be distinct instances of the blueprints. Docsity.com OOP Process • OO Programming involves using existing classes (Buttons, String), and sometimes we define new classes. • Define class (clsOrder) – Define variables: strDescription, intQty, decPrice – Define methods: set and get Description, Qty, Price • Program 1: – Declare an object of the type clsOrder • Program 2: – Declare an object of the type clsOrder • Both include the same properties and methods. • The objects based on clsOrder will be standardized across the programs that use the clsOrder class. Docsity.com Date Class Designed • We can create a class to handle dates and the class may support: – Data validation for the month, day, year. – Date displayed in different formats. • Designs of Object-Oriented Programs can be represented using Unified Modeling Language (UML). • Class designs are displayed using UML Class Notation. Docsity.com UML – Class Notation • Notation: - private + public # protected Class name Properties (variables) - + # Operations (methods) - + # Docsity.com Class Outline • Class Name • Properties (variables) – Properties are used to record the current state of an object. – The values in the variables represent the current state. • Operations (methods) – Operations are used to modify the values of the members variables. – C# uses Property Blocks to set and get values stored in properties (variables). Docsity.com Date Class Notation DateMDY +month +day +year +getDate() • Notation: - private + public # protected Docsity.com DateMDY Definition public class DateMDY { public int intMonth, intDay, intYear; public string getDate( ) { return (intMonth.ToString(“N0”) + “/” + intDay.ToString(“N0”) + “/” + intYear.ToString(“N0”) ); } } //This class cannot be executed. //It is merely a definition for other programs to use. Docsity.com Declaring an Object • An object is a variable declared using a class as the data type. • Declaring a primitive variable. dataType variableName; decimal decPrice; • Declaring an object. ClassName objectName = new ClassName( ); DateMDY bday = new DateMDY( ); Docsity.com Textbox Class Review • A textbox is a class that has properties (.Text). txtName.Text = strEmpName; • A textbox is a class that has methods (.Focus). txtName.Focus( ) Docsity.com Using DateMDY Class private void btnProcessBday (…) { DateMDY bday = new DateMDY( ); bday.intMonth = 10; bday.intDay = 31; bday.intYear = 1980; txtDate.Text = bday.getDate( ); } Docsity.com Multiple Objects • You can create many instances/objects of a class in the same program. • Each object will have their own memory allocation. DateMDY bday = new DateMDY( ); DateMDY dueDate = new DateMDY( ); • Member variables are also known as instance variables. – Their values are not shared among objects. Docsity.com Improved DateMDY Class DateMDY -month (now private) -day -year +setMonth +getMonth +setDay +getDay +setYear +getYear +getDate • Notation: - private + public # protected Docsity.com Improved DateMDY Definition public class DateMDY { private int intMonth, intDay, intYear; public int Month { get { return intMonth; } set { intMonth = value; //value required keyword } } //need property procedures for Day and Year public string getDate( ) As String { return (intMonth.ToString(“N0”) + “/” + intDay.ToString(“N0”) + “/” + intYear.ToString(“N0”) ); } } Docsity.com Using Set Methods DateMDY bday = new DateMDY( ); bday.Month = 10; //use property block names to assign bday.Day = 31; //Automatically calls set method bday.Year = 1980; txtDate.Text = bday.getDate( ) //following is now illegal because intMonth is private. bday.intMonth = 11; //intMonth exists, but cannot be referenced directly. Docsity.com Date Considerations • Increase days first, then month, then year. • Leap year? • Display date in various formats: – MM/DD/YYYY – Month DD, YYYY – Etc. • Before taking this example too far, you should know that C# includes a DateTime class… Docsity.com • Let’s take a look at the example, CS8ex. Docsity.com Read-Only Properties • This is used for variables that are maintained by the class, but may need to provide the value to the program at some time. • This could be used on running totals, counts, or constants used in the class. • The getDate method could be converted to a Read-Only Property. • To create a Read-Only property, only code the get method of the Property Block. Docsity.com Instance vs. Static (Shared) Variables • Variables defined in a class are normally considered Instance variables. • Each object created would have separate memory allocations for their own variables. • A static variable is a single variable for all objects. • It can be used to keep a running total, count, or it could be a constant. • Static members can be accessed without instantiating an object of the class. • Static members must be referenced using the ClassName even when an instance of the class has been created (ClassName.member) • Methods that reference a static variable should also be declared as static so they can referenced without creating an instance. • Methods that are declared as static, must only reference class variables that are static and/or local variables Docsity.com Defining Static public class DateMDY { //The current date is needed for all instances of DateMDY //We would need to assign the system date to these variables private static intCurrMonth, intCurrDay, intCurrYear; public static string CurrentDate { get { return (intCurrMonth.ToString(“N0”) + “/” + intCurrDay.ToString(“N0”) + “/” + intCurrYear.ToString(“N0”) ); } //No Set because it is read only. } } Docsity.com Using Static Variables DateMDY bday = new DateMDY; DateMDY dueDate = new DateMDY; //Static properties and methods are called using class name. lblCurrDate.Text = DateMDY.CurrentDate //There would be one CurrentDate for both bday. and dueDate. //and both have the same value Docsity.com Default Constructor • Default constructor has no parameters. • Always define a default constructor, even if it will not be doing any initialization. • If one is not defined, the compiler will generate one. • Usually used to assign a default value. public DateMDY ( ) { intMonth = 1; //assign default date intDay = 1; intYear = 1900; } Docsity.com Overloaded Constructors • Constructors can be overloaded. – Same method name but a different number or type of parameters. • Initial values can be passed at declaration if there is a parameterized constructor defined. public DateMDY (int m, int d, int y) { intMonth = m; intDay = d; intYear = y; } Docsity.com Property Blocks and Constructors • Use property blocks by using the property name, because any validation would be performed in the set method. public DateMDY (int m, int d, int y) { Month = m; //calls set procedure Day = d; Year = y; } Docsity.com Using Default Constructors public DateMDY ( ) { intMonth = 1; //assign default date intDay = 1; intYear = 1900; } • In the declaration below determine why is the default constructor called and what is returned by Date property. DateMDY bday = new DateMDY( ); txtDate.Text = bday.Date; Docsity.com Using Overloaded Constructors public DateMDY(int m, int d, int y) { Month = m; //calls set method Day = d; Year = y; } • In the declaration below determine why the overloaded constructor is called and what is returned by Date property. DateMDY payDate = new DateMDY(2, 26, 2002); txtDate.Text = payDate.Date; Docsity.com Destructor • A method that is automatically called when object goes out of scope. • Must be public. • The name of method is the class name preceded with a tilde (~) ~DateMDY( ) • Can NOT return a value. • Can be used to “cleanup” dynamic variables. • It is recommended that we do not declare one unless it is required, because the .Net Framework performs it own garbage collection (releases memory). Docsity.com Data Validation Definition public string Description { get { return mstrDescription; } set { if (value ! = “”) mstrDescription = value; else throw new System.Exception(“Description is missing.”); } } Docsity.com Data Validation Usage private void btnProcess(…) { try { objOrder = new clsOrder; objOrder.Description = txtDescription.Text; //… additional processing here } catch ex As Exception { MessageBox.Show("Error: " + ex.Message); } } Docsity.com Summary • Object-Oriented Programming (OOP) • Class vs Object • Unified Modeling Language (UML) • Defining Classes • Using Classes • Read-Only Properties • Instance vs. Static (Shared) • Constructors and Destructors Docsity.com