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Notes on C#
BY: MATT BOGGUS
SOME MATERIAL BASED ON ROGER CRAWFIS�� C#
SLIDES

C# and Java similarities
All classes are objects
? Compare System.Object to java.lang.Object
Similar compilation and runtime to Java
? Compare Java Virtual Machine to Common Language Runtime
Heap-based allocation
? Use ��new�� keyword to instantiate
? Automatic garbage collection

C# language features
Namespaces
Classes
? Fields
? Properties
? Methods
? Events
Structs
Enums
Interfaces
? Methods
? Properties
? Events
Control Statements
? if, else, while, for, switch, foreach

Classes vs. structs
Both are user-defined types
Both can implement multiple interfaces
Both can contain
? Data
? Fields, constants, events, arrays
? Functions
? Methods, properties, indexers, operators, constructors
? Type definitions
? Classes, structs, enums, interfaces, delegates

Classes vs. structs
CLASS ; REFERENCE TYPE
Reference type
Original instance of the object
can be modified during
execution of method bodies
STRUCT ; VALUE TYPE
Value type
A copy of the object is made
and operated on inside method
bodies
Many types in XNA and MonoGame are defined as structs (ex: Vector2 and Rectangle)
Can pass structs as reference type using ��ref�� keyword

Interfaces
An interface defines a contract
? An interface is a type
? Contain definitions for methods, properties, indexers,
and/or events
? Any class or struct implementing an interface must
support all parts of the contract
Interfaces provide no implementation
? When a class or struct implements an interface it must
provide the implementations
? SOLID: Depend upon abstractions not concretions

Interfaces
��Rigid�� interface
? Functionality is explicitly defined
? Ex: OSU Component Library where interfaces include Javadoc comments
with methods�� requires and ensures clauses (pre and post conditions)
��Flexible�� interface
? Only method signatures are specified
? Ex:
IBird interface defines void Fly()
Duck class implements void Fly { position.y += 5; }
Penguin class implements void Fly { // no-op }

public interface IDelete {
void Delete();
}
public class TextBox : IDelete {
public void Delete() { ... }
}
public class ImageBox : IDelete {
public void Delete() { ... }
}
TextBox tb = new TextBox();
tb.Delete();
Interface example
IDelete deletableObj = new ImageBox();
deletableObj.Delete();
deletableObj = new TextBox();
deletableObj.Delete();

Abstract class
Similar to interfaces
? Cannot be instantiated
? In some cases, contain no executable code
? Can contain method headers/signatures and properties (more on
these in a bit), but unlike interfaces they can contain concrete
elements like method bodies and fields
Some quirks when working with abstract classes and interfaces
? A class that is derived from an abstract class may still implement
interfaces
? A concrete class may implement an unlimited number of interfaces,
but may inherit from only one abstract (or concrete) class

public abstract class Shape
{
protected int x = 50;
protected int y = 50;
public abstract int Area();
}
public class Square : Shape
{
public int width;
public int height;
public override int Area()
{
return width * height;
}
public void MoveLeft()
{
x--;
}
}
Abstract class example
Methods marked as abstract have no
bodies and must be overridden
Methods marked as virtual have
bodies and may be overridden
See http://msdn.microsoft.com/en-
us/library/sf985hc5.aspx for a longer
example

this
The this keyword is a predefined variable available in non-static function
members
? Used to access data and function members unambiguously
public class Person
{
private string name;
public Person(string name)
{
this.name = name;
}
public void Introduce(Person p)
{
if (p != this)
Console.WriteLine(��Hi, I��m �� + name);
}
}

base
The base keyword can be used to access class members that are hidden
by similarly named members of the current class
public class Shape
{
private int x, y;
public override string ToString()
{
return "x=" + x + ",y=" + y;
}
}
public class Circle : Shape
{
private int r;
public override string ToString()
{
return base.ToString() + ",r=" + r;
}
}

Fields
A field or member variable holds data for a class or struct
Can hold:
? A built-in value type
? A class instance (a reference)
? A struct instance (actual data)
? An array of class or struct instances
(an array is actually a reference)
? An event

Field examples
static and instance
Output is:
20
2
30
2
public class NumStore
{
public static int i = 10;
public int j = 1;
public void AddAndPrint()
{
i=i+10;
j=j+1;
Console.WriteLine(i);
Console.WriteLine(j);
}
}
public class Exercise
{
static void Main()
{
NumStore x = new NumStore();
x.AddAndPrint();
NumStore y = new NumStore();
y.AddAndPrint();
Console.ReadKey();
}
}

Properties
Client side looks like a field
Internally behaves like method calls to get or set the field (i.e. more
abstract than a field)
Properties encapsulate a getting and setting a field
? Useful for changing the internal type for a field
? Useful for adding code or breakpoints when getting/setting a field

Properties �C syntax examples
type PropertyName { get; set; }
Many valid formats
int Score { get; set; }
string Name { get; }
double Time { get; private set; }
Code examples
? Person*.cs examples [Compare maintainability]
? http://www.dotnetperls.com/property

Modifiers
Public
? Accessible anywhere
Protected
? Accessible within its class and by derived class instances
Private
? Accessible only within the body of the class
? (Or anywhere if you use reflection)
Internal
? Intuitively, accessible only within this program (more specific definition here)
? The default, but you should generally pick public or private instead

Access modifier error example
Cannot have an interface that is less accessible than a concrete class that
implements it (also applies to base and inheriting classes)
interface GameObject // no access modifier, defaults to internal
{
void Draw();
void Update();
}
public class Monster : GameObject
{
// ... implementations of Draw() and Update() go here ...
}

End of lecture
ADDITIONAL ON YOUR OWN SLIDES FOLLOW

Why C#?
Fits with
? .NET framework
? Large library of features and objects; portable and integrates with software written in
other languages
? Visual Studio
? Single point of access for software development, source code control, project
management, and code reviews
Additional reasons
? Game engines support C# -> XNA, Monogame, Unity
? Used in other CSE graphics courses (Game and Animation Techniques; Game
Capstone)
? More discussion of pros/cons of C# here
? More discussion of pros/cons of C# specific to game development here; this
subset of comments has some good insights

On your own
Java to C# resources
The C# Programming Language for Java Developers �C documentation of
language differences organized by programming constructs
Additional Suggestions from StackOverflow

public class Car : Vehicle
{
public enum Make { GM, Honda, BMW }
private Make make;
private string vid;
private Point location;
Car(Make make, string vid, Point loc)
{
this.make = make;
this.vid = vid;
this.location = loc;
}
public void Drive()
{ Console.WriteLine(��vroom��); }
}
Car c =
new Car(Car.Make.BMW,
��JF3559QT98��,
new Point(3,7));
c.Drive();
Class syntax example

How many methods should
classes/interfaces provide?
On your own references
Keep it simple!
? The Magical Number Seven, Plus or Minus Two
? The average person can hold 7 �� 2 objects in memory at a time
? Experts recall more by ��chunking�� C combining multiple objects
into one
? Think You're Multitasking? Think Again
? The average person is bad at multi-tasking, so focus on what you��re
doing if you want it done well

Conversion operators
Can also specify user-defined explicit and implicit conversions
public class Note
{
private int value;
// Convert to hertz �C no loss of precision
public static implicit operator double(Note x) {
return ...;
}
// Convert to nearest note
public static explicit operator Note(double x) {
return ...;
}
}
Note n = (Note)442.578;
double d = n;

The is Operator
The is operator is used to dynamically test if the run-time type of an
object is compatible with a given type
private static void DoSomething(object o)
{
if (o is Car)
((Car)o).Drive();
}

The as Operator
The as operator tries to convert a variable to a specified type; if no such
conversion is possible the result is null
More efficient than using is operator
? Can test and convert in one operation
private static void DoSomething(object o)
{
Car c = o as Car;
if (c != null) c.Drive();
}

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