Object-Oriented Programming

1. Object-Oriented Programming

2. Agenda • Classes & Objects • Attributes • Methods • Objects in memory • Visibility • Properties (get & set) • Constructors

3. Classes • Encapsulate data and functions • Enable more complex programming • Large-scale programming • Requires “Object think” • Security/reliability • Design by contract

4. Defining a Class class NAME { ATTRIBUTES (data) METHODS (functions) }

5. Class Example class BMW_Z4 { int ModelYear; string LicensePlate; bool TopUp; void Drive() { Console.WriteLine(“Roadin’ and Rockin’“); } void OpenTop() { TopUp = false; } }

6. Class Example class BMW_Z4 { int ModelYear; string LicensePlate; bool TopUp; void Drive() { Console.WriteLine(“Roadin’ and Rockin’“); } void OpenTop() { TopUp = true; } } Attributes (data) Methods(functions)

7. Instantiating Classes • Defining the class is akin to defining a type • An object is an instance of a class • Class:Object::Type:Variable • Use new() to instantiate the class

8. Instantiating Class & Using Object BMW_Z4 myCar; myCar = new BMW_Z4(); myCar.LicensePlate = "BMR4ME"; myCar.ModelYear = 2004; myCar.Drive(); myCar.OpenTop(); myCar.Drive();

9. Memory Trace Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; null

10. Memory Trace(declare the variables; they are dead) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; null d2 d1

11. Memory Trace(bring d1 to life) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; // Remember, new opens // up space and calls the // class constructor null d2 d1

12. Memory Trace(bring d1 to life) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; // Remember, new opens // up space and calls the // class constructor null d2 d1

13. Memory Trace(bring d1 to life) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; // Remember, new opens // up space and calls the // class constructor null d2 d1 rabid=false weight=5 name=“bob”

14. Memory Trace(bring d2 to life) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; // Remember, new opens // up space and calls the // class constructor null d2 d1 rabid=false weight=5 name=“bob”

15. Memory Trace(bring d2 to life) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; // Remember, new opens // up space and calls the // class constructor null d2 d1 rabid=false rabid=false weight=5 weight=5 name=“bob” name=“bob”

16. Memory Trace(comparison) Memory d1 and d2 do NOT occupy the same space in memory, so they are NOT == Example: d1 == d2 evaluates to false null d2 d1 rabid=false rabid=false weight=5 weight=5 name=“bob” name=“bob”

17. Memory Trace(have d1 point to d2) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; null d2 d1 rabid=false rabid=false weight=5 weight=5 name=“bob” name=“bob”

18. Memory Trace(have d1 point to d2) Memory Dog d1, d2; d1 = new Dog (5, “bob”); d2 = new Dog (5, “bob”); d1 = d2; null d2 d1 rabid=false rabid=false weight=5 weight=5 name=“bob” name=“bob”

19. Memory Trace(have d1 point to d2) Memory Now, d1 and d2 are == But no one is pointing to this Because no one is pointing to it, we can no longer reference it. We call this piece of memory garbage. The garbage collector will deallocate it. null d2 d1 rabid=false rabid=false weight=5 weight=5 name=“bob” name=“bob”

20. Visibility • OO motivation: protection/security • We need a way of selectively “publishing” parts of a class and “hiding” other parts of the class • Public & private

21. VisibilityExample class BMW_Z4 { private int ModelYear; public string LicensePlate; private bool TopUp; public void Drive() { Console.WriteLine("Roadin’ and Rockin’"); } public void OpenTop() { TopUp = false; } } Note the visibility change(most attributes will be private) Method aretypically public

22. Object Method & Attribute Visibility BMW_Z4 myCar; myCar = new BMW_Z4(); myCar.LicensePlate = "BMR4ME"; myCar.ModelYear = 2004; myCar.Drive(); myCar.OpenTop(); myCar.Drive(); Illegal b/c private

23. Properties • Combines field/attribute with method • Standard: • Make attributes private • Lower-case first letter of attribute • Make properties public • Upper-case first letter of properties • Define “get” and “set” for each property (selectively)

24. PropertiesExample class BMW_Z4 { private int modelYear; private string licensePlate; private bool topUp; public int ModelYear { get { return modelYear; } set { if (value >= 2003) modelYear = value; } } public string LicensePlate { get { return licensePlate; } set { if (value.Length() == 6) licensePlate = value; } } ... }

25. Constructors • So far, we’ve seen attributes and methods • Constructor is a unique method • Named same as the class name • Automatically called when class is instantiated • Useful for setting attributes & initializing the instance • No return type (not even void) • Must be public • Default constructor is used unless you specify a constructor • For each attribute in the class, assign something to it in the constructor (initialize)

26. ConstructorExample class BMW_Z4 { private int modelYear; private string licensePlate; private bool topUp; public BMW_Z4 () { ModelYear = 2004; TopUp = false; LicensePlate = "DEALER"; } ... }

27. FIN