1 / 38

C# and Types

C# and Types. A chic type, a rough type, an odd type - but never a stereotype Jean-Michel Jarre. Review & Context. Types are defined by CLR, hence it is same across languages Two phases of .Net learning Basics – CLR, types, Language syntax VB.Net or C#

Télécharger la présentation

C# and Types

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. C# and Types • A chic type, a rough type, an odd type - but never a stereotype • Jean-Michel Jarre More Types & C#

  2. Review & Context • Types are defined by CLR, hence it is same across languages • Two phases of .Net learning • Basics – CLR, types, Language syntax VB.Net or C# • Application – ADO.Net, ASP.Net, Windows Forms. More Types & C#

  3. C# • C# aims to combine the high productivity of Visual Basic and the raw power of C++ • Microsoft outsiders claim – “C# as Microsoft's alternative to Java” • Although .Net supports all languages equally – c#, vb.net, jscript.net etc. Many companies like to pick one. • VB.Net and C# syntax comparisonhttp://www.visualbasicexpert.com/vbvscsharp.htm More Types & C#

  4. Basics • CaSe SeNSitiVE • Comments//, /* */ or /// • /// use used for code documentation • Identifiers: • Don’t use underscores, abbreviations • Follow guidelines:Camel case for variablesPascal case for Class names, methods, properties and namespaces EmployeeName employee_name localVariable XMLReader XmlReader More Types & C#

  5. Operators More Types & C#

  6. Blocks • Variable scope is limited to blocks • Blocks are delimited by braces • In the example below s each block refers to a different variable. { string s; } { string s; } More Types & C#

  7. Control flow • if statement – similar to c, c++ or java • Note the parenthesis after ‘if’ • Do we need a braces for if?Answer: Only for compound statements if (i>0) string s = “greater”else string s = “smaller” if ( boolean-expression ) embedded-statement else embedded-statement More Types & C#

  8. Control Flow (contd.) • Switch statement – similar to c, c++ and java • Can switch on a string • Watch out for fall-through void Func(string option) { switch (option) { case "label": goto case "jump": case "jump": goto default; default: break; } } More Types & C#

  9. Control Flow • while and for - similar to c, c++ and java • foreach – new construct, used for collections, arrays. ArrayList numbers = new ArrayList(); ... // fill numbers with 0 through 9 ... foreach (int number in numbers) { Console.Write("{0} ", number); } More Types & C#

  10. More Value Types • Recall value types are allocated on stack • struct – user defined value type • How are structures different from classes?Answer: since they live on stack they are fast, highly efficient. Hence, use structs only when you need performance struct Point { public int X, Y; }; More Types & C#

  11. Reference Types More Types & C#

  12. String Type • string is an alias for System.String • Immutable – just as in java • They are allocated on the heapDraw memory model picture for string s = “hello”; • They are NOT array of characters. • StringBuilder • Represents a mutable character string • Used when a strings need to be modified repeatedly. More Types & C#

  13. String Type (contd.) • Literals, two ways: • Quoted • @ Syntax //Quoted string s = “hello”; // 2 backslashes to avoid escape sequence string path = “c:\\temp”; //@Syntax string path = @”c:\temp”; More Types & C#

  14. String Type (contd.) • Operators • Equality (==), concatenation (+=), indexer [ ] are overloaded • Equality (==) operator works differently in java. string s = “hello”; if (s == “hi”) // equality, comparison .. s += “ world” // concatenation char c = s[1]; // array type access More Types & C#

  15. Class Type • User defined reference type • Notice the naming conventions class Employee { private string name; private decimal salary; public decimal SalaryCap = 10000.00M; //default access is private string secretary; } More Types & C#

  16. Constructor • Compiler declares a default c'tor • You can declare the default c'tor • If you declare a c'tor the compiler doesn't class Employee { private string name; private decimal salary; public Employee(string n, decimal d) { name = n; salary = d; } public Employee(string n) // call other c’tor :this(n, 0.0M) { } } More Types & C#

  17. Fields • Instance fields • they belong to the object instance • one per object. E.g.. Name, Salary in Employee class. • Readonly fields – use keyword readonly • Should be initialized at declaration time or in c’tor. • Static fields – use keyword static • They belong to the class type • Access only via class name • Const fields - use keyword const • are implicitly static • only simple types, enums, & string can be const • const fields require a variable initializer More Types & C#

  18. Fields (Contd.) • Employee Class class Employee { //instance fields private string name; private decimal salary; public readonly decimal SalaryCap = 10000.00M; public const int StartEmpNum = 1000; } More Types & C#

  19. Object Creation • Use new keyword • Call constructor • Draw memory map for the following: class Employee { //instance fields private string name; ... // Entry point public static void Main() { Employee e1 = new Employee(“John"); Employee e2 = new Employee("Mary", 11000); Employee e3 = new Employee(); //Error ??? } } More Types & C#

  20. Passing parameters • By copy • Default • No special keyword • By reference • ref keyword • Out parameter • out keyword • Gives write access More Types & C#

  21. Arrays • Arrays are reference types, they allocated on the heap // Array declaration int[] myArray = null; int[,] myArray2; // 2 dimensional Employee[] staff; // Array allocation int[] myArray = new int[4]; int[,] myArray2 = new int[2,3]; //declaration, allocation and initialization int[] myArray = new int[4] {1,2,3,4}; int[] myArray = {1,2,3,4} //shortcut More Types & C#

  22. System.Array • All arrays are derived from System.Array type • It has some important properties: • Length, number of elements • Rank, number of dimensions • Important methods: • Copy • Sort • Clear • BinarySearch More Types & C#

  23. params keyword • C# allows variable number of parameters for a method public void PrintMe(params int[] val) { … } public void Main() { PrintMe(1); PrintMe(2, 3); PrintMe(3, 5, 5); } More Types & C#

  24. Inheritance • A class can inherit from a single base class • By default methods are not virtual • struct cannot inherit from a struct or class • There is no extends keyword as in java public class Vehicle { … } public class Car:Vehicle {… } More Types & C#

  25. Inheritance From a base class perspective • virtual method • Method may be replaced by derived class • abstract method • Method must be replaced a derived class • sealed method • A method may not be replaced by a derived class • override method • Method replace a method in the parent (base) class. It is still overridable by further derived classes. • new method • Method is unrelated to a similarly defined method in the parent class. Used when there is a change made to the base class resulting in name clash in the child class. From a derived class perspective More Types & C#

  26. Inheritance • A class can call its parent constructor using base keyword class Manager:Employee { public Manager(string n) :base(n) {} } More Types & C#

  27. Inheritance Example public class Employee{ public static void Main(){ Employee e = new Employee(); e.RaiseSalary(5); //calls employees raise method Manager m = new Manager(); m.RaiseSalary(5);//calls manager method m.GenerateID(); //calls employees method } // may be overridden public virtual void RaiseSalary(double percent){ } // statically bound cannot be overridden public void GenerateID() { } } public class Manager: Employee { // specialized method for Manager only public override void RaiseSalary(double percent){ } } More Types & C#

  28. Abstract Class • A class that cannot be instantiated • It is useful when you derive from it abstract class Vehicle { } class Car: Vehicle { } ... { Vehicle v = new Vehicle(); // error Car c = new Car(); //Ok } More Types & C#

  29. Interface • Interface contains method signature only • It serves like a contract interface IBoardMember { public int StockOptions(); // no implementation } //Executive is agreeing to the “contract” in IBoardMember class Executive: Manager, IBoardMember { //class executive has to implement StockOptions public int StockOptions() {... } } More Types & C#

  30. Interfaces • Popular Interfaces • ICloneable • IDisposable // achieves object copying (deep copy) class ICloneable { public Object Clone(); } // achieves object cleanup class IDisposable { public void Dispose(); } More Types & C#

  31. Object • Everything is derived from System.Object • object is alias for System.Object • Even value types- structs, enums, int32 • Does this pose a overhead? • inheritance always has extra processing? • Answer: The framework uses special techniques, value types (int32 etc.) do not directly inherit from object • Exercise: • Check what methods are available on System.Object More Types & C#

  32. Down Casting • A reference to base type can refer to any of its derived types • Other way is not allowed • Hence, a reference to object type can refer to any object { Employee e; Manager m = new Manager(); e = m; //allowed, down casting Employee e2 = new Employee(); m = e2; // not allowed } More Types & C#

  33. Exception Handling • Exception is a class that represent errors during application execution. • All Exceptions inherit from System.Exception • This replaces arcane error codes used in legacy systems • Exercise: • List 5 exceptions derived from System.Exception in the .Net framework More Types & C#

  34. try-catch syntax try { // try to read a text file StreamReader sr = new StreamReader("TestFile.txt"); string line; while ((line = sr.ReadLine()) != null) { Console.WriteLine(line); } } // if error come here // ex contains all the info about error catch (IOException ex) { Console.WriteLine(ex.StackTrace); } // finally is always executed finally { sr.Close(); } More Types & C#

  35. Delegates • A delegate declaration defines a reference type that can be used to encapsulate a method with a specific signature • A delegate lets you pass a function as a parameter • Just like in declaration “string s;” s can point to any string, “MyDelegate” can point to any method which takes a integer parameter. // delegate declaration delegate void MyDelegate(int i); More Types & C#

  36. Delegate // delegate declaration delegate void MyDelegate(int i); class Program{ public static void Main(){ TakesADelegate(new MyDelegate(DelegateFunction)); } public static void TakesADelegate(MyDelegate SomeFunction) { SomeFunction(21); } public static void DelegateFunction(int i) { System.Console.WriteLine("Called by delegate with number: {0}.", i); } } More Types & C#

  37. Events • A delegate field can be marked as an event • Widely used in GUI classes • only += and -= can be performed on the field More Types & C#

  38. Attributes • Attributes allow code elements to be tagged with declarative information • They are can queried using reflection [DeveloperName(“John B”)] public class MyClass { … } More Types & C#

More Related