1. Object-Oriented Programming

2. Agenda
Static
Const
Overloading
Inheritance

3. Static
Each instance of a class (called an object) has a copy of the attributes
Changing an attribute in one object doesn’t affect the attribute of another object
But what if we want persistence (shared) among all instances?

4. Static Variables void PrintNumbers () {
static int count = 0; // this is only set to 0 ONCE
Console.WriteLine(count);
count++; }
static void Main()
...
for(i=0; i < 50; i++)
PrintNumbers();

5. Static Attributes class BMW_Z4 { private static int VehicleId = 0;
public int MyID;
public BMW_Z4 ()
MyID = VehicleId;
VehicleId++; }
...
static void Main()
BMW_Z4 my_z4 = new BMW_Z4(); // has VehicleId of 0
BMW_Z4 your_z4 = new BMW_Z4(); // has VehicleId of 1

6. Const Variables are just that – variable
They can be changed programmatically via the assignment operator (=)
But there are times when some values should be immutable
Preface the declaration with “const”
Cannot be changed – EVER!

7. Const Example class BMW_Z4 { public const int MaxSpeed = 185;
private int currentSpeed;
public void Accelerate
currentSpeed += 5;
if (currentSpeed > MaxSpeed)
currentSpeed = MaxSpeed; }
...

8. Overloading Overloading involves using the same method/function name
Vary the number of parameters
Vary the type of parameters
Cannot just change return type (ambiguity in invocation)
Useful to keep things simple
Squaring a number…

9. Overloading Example int Square (int i) { return i * i; }
float Square (float i)
static void Main()
...
float x = Square(5.3);
int y = Square(9);

10. Operator Overloading Notice same method name, different parameters
class BMW_Z4 {
...
public BMW_Z4 ()
Initialize(0, 2004, false); }
public BMW_Z4 (int my)
Initialize(0, my, false);
private Initialize(int cs, int my, bool tu)
currentSpeed = cs;
ModelYear = my;
TopUp = tu;
Notice same method name, different parameters
Place common initialization in a separate function

11. Inheritance
Inheritance allows one class to take on the properties of another
Superclass-subclass relationship
Sometimes called parent-child relationship
Use the keyword extends to express this relationship
Subclass will “inherit” certain attributes and methods
Benefit: good design, reuse of code

12. Class Hierarchy Mammal LandMammal Dog Chihuahua SheepDog int weight
giveBirth( )
LandMammal
int numLegs
Question: how many
attributes does Dog
have?
Dog
boolean rabid
Chihuahua
SheepDog

13. Things to Note
LandMammal is a superclass to Dog, but a subclass to Mammal
Dog has three attributes
weight, numLegs and rabid
Two from inheritance, one it declared itself

14. Visibility and Inheritance
Public – allows all to see
Private – allows only class in which defined to see
Protected – allows class and all subclasses that inherit to see
Consequently, we’ll now use protected instead of private by default… (common)

15. C# Syntax Notice the use of “:” class Person { ... }
class Student : Person
class Professor : Person
Notice the use of “:”

16. The Base Class: “Object”
All classes in C# inherit (sometimes implicitly) from Object
Includes common set:
ToString()
GetType()
Equals()
Often useful to override (implement) these virtual functions
“public override string ToString()…”

17. FIN