Transcript Document

C#
.NET
C# language
C#
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A modern, general-purpose object-oriented language
Part of the .NET family of languages
ECMA standard
Based on C and C++
.NET
• Multiple languages which can interoperate
• Languages compile to a common
intermediate language
• Common Language Runtime runs programs
from all the .NET languages
C# versus Java
• Both were designed to be improvements on C and
C++
– Java aims to be one language for many platforms
• portable (platform-independent)
• safe
– C# aims to provide many languages for a single platform
• power
• unsafe code is allowed
• platform-independent not
Language Features
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Strong type checking
Array bounds checking
Detection of uninitialized variables
Automatic garbage collection
Designed for use in distributed environments
Supports internationalization
First Program
namespace FirstProgram {
class First {
static void Main() {
System.Console.WriteLine(
"Welcome to C#!");
}
}
}
C# on onyx
• mono is an open-source project that provides
facilities for running C# programs under Linux
http://www.mono-project.com
• Workstations have a Windows virtual
machine with C# Express installed
mono
• mono is an open-source project that provides
facilities for running C# programs under Linux
http://www.mono-project.com
• Compile a program by typing
mcs First.cs
• Run a program by typing
mono First.exe
C# Express
• VMWare is installed on all the workstations in
the lab
– Not on the server
– Virtual machine is frozen
Getting your own copy
• C# Express
– Free from Microsoft
– http://www.microsoft.com/express/vcsharp/
• .NET Development Environment
– Available to you through MSDN Alliance
– details later
C# Program Structure
• A program consists of one or more files
• A file can contain one or more classes and/or
namespaces
– name of file is not tied to name of class
• At least one class must contain Main
– There are several allowed signatures
• return type is either int or void
• either no parameter or String array
C# Types
• Value types
– simple types: primitive types from Java plus
unsigned types and decimal
• Reference types - like object references in
Java
• Pointer types - used only in unsafe code
• Everything can be treated as an object
Operators
• Java operators with similar precedence
• Extra operators
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typeof - returns class name (getClass())
checked/unchecked (overflow)
is (like instance of)
as (returns cast value or null)
• Unsafe operators
– *, &, sizeof
Operators: differences from Java
• C# allows you to overload operators
• == compares values for strings and simple
types, addresses for all other objects
Console I/O
• System.Console.WriteLine( arg)
– argument can be any type
– for objects, ToString is invoked
• System.Console.ReadLine()
– returns a String
• System is a namespace
– using System; allows you to omit the
namespace when calling the method
Namespaces
• Sort of like a package
– in Java, package statement applies to everything
in the file
– can import all or part of a package
• A single C# file can contain classes from
different namespaces
– using imports entire namespace
C# Class Members
• Data Members
– Field
• instance
• static
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Constant
Read-only
Delegate
Event
• Function Members
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Instance constructor
Static constructor
Method
Property (accessor/mutator)
Indexer
Operator
Destructor (finalizer)
Nested types (inner classes)
C# Class Modifiers
• new
• abstract
• sealed (final)
• access modifiers
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public
protected
internal
private
Inheritance
• Single inheritance (System.Object)
class <class_name>:<super_class> {… }
• Interfaces provide restricted form of multiple
inheritance
interface <interface_name> {… }
– Syntax is same as for inheritance
– Multiple interfaces separated by comma
– Super class, if any, must be first in list
Methods
• Syntax same as for Java
• Default access is private (rather than
package)
• Value types are passed by value usually
– ref keyword used to pass by reference
– out keyword provides for return values
• Reference types behave as in Java
Properties
• C# properties provide the same service as
Java's accessors and mutators
public string Color {
get {return MyColor;}
set { MyColor = value; } }
• Use the name Color to get value of or assign
value to private instance variable MyColor
Control Statements
• do, while, for, if-else same as in Java
• foreach provides loop for arrays
• switch-case like Java except
– string case values are allowed
– no fall-through behavior
• use goto case <label> instead
• C# has goto statement
Arrays
• Arrays are objects
– Subclasses of System.Array
– Reverse, Sort, IndexOf methods
• Declaration, instantiation, initialization, element
access as in Java for 1D arrays
int []MyArray = new int[5];
– Length property gives the number of elements
– Only this syntax is allowed
Arrays
• For rectangular 2D arrays
int [,] Array2D = new int[2,5];
– Length property gives total number of elements
– Element access is the same as in Java
• For jagged arrays
int [][] JaggedArray2D = new int[2][];
JaggedArray[0] = new int[3];
Structs
• A struct is very similar to a class except
– structs are value types, classes are reference
types
– no inheritance
– struct has a default constructor always
– all constructors must initialize all data
– can be "instantiated” without new
Exceptions
• System.Exception
• try-catch-finally has same syntax as Java
– Don't need a variable name in catch if you aren't
going to use it
– Within catch block, throw throws the exception that
was caught
• All exceptions are unchecked
Delegates
• Delegate is a special type that encapsulates
one or more methods
public delegate int MyDelegate( string
s, int i);
• Instantiate with a method that has the same
signature and return type
MyDelegate d2 =new
MyDelegate(obj.ObjectMethod);
Events
• C# event model is similar to Java - delegation
based
• An Event is a special type of Delegate
• Event is created by event source when an
event occurs. The Event is passed to the
event consumer's handler
• Handlers must be registered with the event
source
etc.
• Operator overloading
• Reflection - asking a class for information
about it
• Attributes
– Used to add annotation to a class that can be read
using reflection
• Preprocessor
• Unsafe code