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Teaching with C Sharp
Rob Miles
Overview
Introduction> My perspective
C# and Java> Broad overview of the languages
Significant C# Features> C# features from a teaching perspective
Conclusion> ..and possibly a sing song?
Introduction
The material is based on my experience teaching C# to two student cohorts
It is necessarily coloured by my teaching philosophy
It has been presented in targeted sections so that you can use those components which suit your purpose
There are number of sample projects for each section which form the basis of the lab work
Presentation Notes
A full set of notes is provided for this presentation
The notes are broken down in the same sequence as the items given here
Each section is followed by a number of practical examples along with some ideas for investigation
Bonus Materials
As this is the “collectors edition” of the course> Just like every other edition…
It is supplied with bonus materials in the form of a copy of “C# from Java”
This provides an FAQ for a number of conversion issues
Teaching Philosophy
At Hull we teach an “algorithms first” course This concentrates on program construction in
semester one and introduces objects in semester two
Everything is placed in the strongest possible “real world” context and I make heavy use of analogies
Objects
Objects are presented as a solution to structure and design
I try to make a logical transition from structures to components:
> Encapsulation> Business Objects> Test driven development> Component based design> Hierarchies for code reuse
Teaching and C#
I have found that C# matches with our teaching philosophy
It would also match with an objects first approach, at least as well as Java does
The points made later are applicable to both teaching approaches
C# and Java
C# is heavily based on Java Conversion from C# to Java (or back) is not
difficult C# programs seem to run faster on the PC
platform C# is not being positioned as Microsoft
proprietary> But the language development is Microsoft driven, in the
same way that Java development is Sun driven
C# Versions
There are now two versions of C# Version 2 adds a number of features:
> Partial classes> Generics
There are few breaking changes moving from C# Version 1 to Version 2
This presentation is Version 1 compliant
Development Tools
A command line compiler kit is available> Directly analogous to the JDK
Visual Studio 2005 is available under the Academic Alliance
Visual Studio 2005 Express Edition is available for free
> David will give more details of these later
C# Language Features
We can consider some specific C# features:> User input/Output> Value Types and Structures> Exception Handling> Reference Parameters> Event Handling/Delegates> Program Linking and Deployment> Properties> Generics
They will be placed into a teaching context
User input/output
The System.Console object provides a range of input/output actions
There is no need to create a stream object There is also no need to trap exceptions
demodemo
Simple Input/Output> Text Read and Write and colour manipulation
Console Power> Moving dot game
Value Types
In Java a type is either primitive or reference: Primitive
> Managed by value> Primitive types do not support methods or properties
Reference> Managed by reference> Support methods and properties> Slower to manipulate
Java Primitive Problems
For a student learning to program the primitive-reference distinction is hard to grasp
It also brings a need to describe the use of wrapper classes
> Students do not like to have to learn the difference between
int and Integer This knowledge is not that relevant to other
languages
C# value types
C# uses a different approach:> All types are objects> Some types are “value” types, i.e. manipulated by value not
reference> But they all support methods and properties> The “box” operation performs conversion from value to
reference as required
The C# student need not be aware of any distinction at the start of the course
demodemo
Value type behaviour in .NET 1.1 and .NET 2.0> Using ildasm to look at the IL
Boxing in Action
static void Main(string[] args){ int a, b; a = 99; b = a; b = 100; Console.WriteLine("a is {0} b is {1}", a, b);
}
Boxing Assembler
Structures as value types
C# supports a struct type This type is directly analogous to the struct in
C A struct is manipulated as a value type This allows data to be grouped together
without a need to cover objects and references
It also allows for more complex exercises
C# Structs
A struct in C# is managed by value. However, they do behave a lot like objects
> They can support methods and properties> They can have constructors> They can even implement an interface
But they do not support inheritance
demodemo
Structures in C#> Simple structures
> Structure “housekeeping”
> Arrays of structures
Exception Handling
In Java you have to handle some exceptions (the checked ones)
> These are thrown by lots of library methods, including input/output
In C# all exceptions are unchecked> If you don’t catch them the run time system will pick them up> This makes things like simple input/output much simpler
demodemo
Exceptions in C#> Simple exception handling
> Creating your own exceptions
Reference Parameters
Unlike Java, where parameters are always passed by value, in C# reference parameters are allowed
This makes programming more efficient It also allows discussion of the meaning of
references without the need to consider objects
demodemo
Reference Parameters> ref parameters
> in parameters
Event handling and delegates
C# provides a delegate type which can be used to create a typesafe reference to a method in an instance of a class
There is no need to create an instance of a class to receive events
Delegates are used to manage system events and the user interface
demodemo
Event handling with delegates> Simple form creation and event management
> Using the Visual Studio 2005 Forms Designer
Delegates and Design
Delegates bring function pointers back into programming
However, they can be deployed in a typesafe manner in a properly managed environment
However, he biggest advantage over Java is that they make interacting with Forms components much easier
Program Linking and Deployment
In Java a program is built at run time> The classpath is used to locate the required components as
the program runs> There is little attention paid at build time to linking issues
In C# the .exe file is an assembly which may make use of .dll library files
> There is a distinct difference between an executable file and a library one
> An exe file will refer to a specific version of a dll when it is built
C# Programs
Only one class in a C# program may contain a Main method to provide the entry point
During the build process the particular libraries to be used must be specifically identified and located
> If you are using Visual Studio the metadata from the assembly can be used in interactive help
C# Linking and Teaching
I place great emphasis on Business Objects and Test Driven Development
The C# linking process fits well with this approach
The students are initially introduced to the process by means of compiler directives
Later they move on to use Visual Studio 2005
demodemo
Using Business Objects> Single workspace containing a number of Visual Studio Projects
The naming of components
Java provides a package mechanism by which a system can be broken down into components
> this is linked to the physical position of the file in a directory hierarchy
> only one public class can placed in each file, and the filename must match the class name
C# does not do this> A class is placed in a “namespace” which is not physically
mapped to storage
C# Namespace
Namespaces are hierarchical A single source file can contain components
from a number of namespaces A namespace can span multiple source files Visual Studio 2005 provides a view of all the
components in a namespace
Partial Classes
These are available in C# Version 2.0 A class can be made to span a number of
source files This allows the developer to partition the
behaviours of a class into a number of separate source files
> Hide the scary bits?
Visual Studio 2005 does this with forms
demodemo
Using Business Objects and Namespaces> Advanced multi-project workspace with business and control objects
Properties
Properties are “syntactic sugar” They provide a convenient wrapper for get
and set behaviour in objects There is no need to use them
> But all of the system library classes do
They are best explained in the context of “making life easier”
demodemo
Simple Properties> A book title class which uses properties to manage the name of the book
Properties and Assembler
Generics
Generics are new in Version 2.0 They let you create classes which work on
classes You don’t have to give the types of the
classes when you write the code Instead you use placeholders which are “filled
in” at runtime in a typesafe manner
Generics and teaching
I would not teach about generics in the first part of a programming course
The fact that they are now present in C# means that we can use this language in later years
Generic Collections
The major advantage that generics brings for learner programmers is a better way to deploy collection classes
They remove the need to cast items read from the collection
> Although I must admit I think that covering casting at this point is a good idea
demodemo
Using the List collection class> A typesafe list collection is created using the new System.Generics.List
collection class
Using Generics
Generics do make it possible to talk about data structures without dwelling on the type of the data being manipulated
This can be rolled into discussions about generalisation which can take place in the latter parts of a first year course
demodemo
Creating and using a generic linked list class> A linked list generic which is deployed for both integers and string types
Conclusion
Students like C#> We have seen improved performance in both coursework
and examinations
It is a more productive programming environment than Java
> All of the language changes are soundly pragmatic> The toolset is very effective and now handles important
issues like test driven development
C# will do very nicely. For now……
Questions
I can take any quick questions now For more detailed ones please catch me in
the break or during the labs