Object-Oriented Programming

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

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

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

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

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

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

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

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

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

Memory Trace (bring d1 to life) 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 d1 d2

Memory Trace (bring d1 to life) 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 d1 d2

Memory Trace (bring d1 to life) 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 d1 d2 rabid=false weight=5 name=“bob”

Memory Trace (bring d2 to life) 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 d1 d2 rabid=false weight=5 name=“bob”

Memory Trace (bring d2 to life) 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 d1 d2 rabid=false weight=5 name=“bob” rabid=false weight=5 name=“bob”

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

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

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

Memory Trace (have d1 point to d2) 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 d1 d2 rabid=false weight=5 name=“bob” rabid=false weight=5 name=“bob”

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

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; } Visibility Example Method are typically public Note the visibility change (most attributes will be private)

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

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)

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; } }... } Properties Example

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)

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

FIN