Object-Oriented Programming

Agenda Static Const Overloading Inheritance

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?

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();

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

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!

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

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…

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);

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

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

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

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

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)

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

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()…”

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