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: Value Type

(User - Defined) struct

(Built - in)

sbyte

byte

short

ushort

intuint

long

ulong

float

double

decimal

char

bool

(User - Defined) enum

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: Reference Type

Reference

Type

class class

string , Exception

interface

array

delegate

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Using Reference-TypeVariables

Comparing Value Types to Reference Types

Declaring and Releasing Reference Variables

Invalid References

Comparing Values and Comparing References

Multiple References to the Same Object

Using References as Method Parameters

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Comparing Value Type to ReferenceTypes

Value Types

The variablecontains the valuedirectly

Examples :char, int

Reference Types

The variablecontains areference to thedata

Data is stored in aseparate memoryarea

int mo1 ;mo1 = 42 ;

string mo1 ;mo1 = "Hello" ;

42 Hello

mo1

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Declaring and Releasing ReferenceVariables

Declaring Reference Variables

Releasing Reference Variables

c1 = null ;

coordinate c1 ;c1 = new coordinate( ) ;c1.x = 6.12 ;

c1.y = 4.2 ; 6.12

c1

4.2

6.12

c1

4.2

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Invalid References

If You Have Invalid References

You cannot access members orvariables

Invalid References at Compile Time

Compiler detects use ofuninitializedreferences

Invalid References at Run Time

System will generate an exceptionerror

- NullReferenceException

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Comparing Values and ComparingReferences

Comparing Value Types ( string )

== and != compare values

Comparing Reference Types ( string )

== and != compare the reference, notthe values

6.12O 4.2

6.12O 4.2

Different

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Multiple References to the SameObject

Two References Can Refer to the SameObject

Two ways to access the same object forread/write

coordinate c1 = new coordinate( ) ;

coordinate c2 ;c1.x = 2.3 ; c1.y = 7.6 ;c2 = c1 ;Console.WriteLine (c1.x + " , " + c1.y) :Console.WriteLine (c2.x + " , " + c2.y);

6.12

c1

4.2

c2

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Using References as Method Parameters

References Can Be Used as Parameters

When passed by value, data beingreferenced may be changed

static void PassCoordinateByValue (coordinate c){

c.x++ ; c.y++ ;}

2 3

c

3 4

loc.x = 2 ; loc.y = 3 ;PassCoordinateByValue (loc) ;Console.WriteLine(loc.x + " , " + loc.y) ;

loc

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class coordinate {

public double x = 0.0; public double y = 0.0; }

static coordinate Example ( coordinate ca,

ref coordinate cb,out coordinate cc )

{ }

static void PassCoordinateByValue (coordinate c) {

{ c.x++; c.y++; }

coordinate loc = new coordinate( );

loc.x = 2; loc.y = 3;

PassCoordinateByValue ( loc );

Console.WriteLine( loc.x, loc.y);

static void PassCoordinateByValue (coordinate c) {

{ c = new coordinate ( );

c.x++; c.y++; }

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Using Common ReferenceTypes

Exception Class

String Class

Common String Methods, Operators, andProperties

String Comparisons

String Comparison Operators

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Exception Class

Exception is a Class

Exception Objects Are Used to Raise Exceptions

Create an Exception object by using new

Throw the object by using throw

Exception Types Are Subclasses of Exception

InvalidCastException, DivideByZeroException..

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String Class

Multiple Character Unicode Data

Shorthand for System.String

Immutable ( )

StringBuilder (mutable : can modify)

string s = Hello ;

s[0] = c : // Compile-time error

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Common String Methods, Operators, andProperties

Brackets

Insert Methods

Length Property

Copy Method

Concat Method

Trim Method

ToUpper andToLower Methods

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String Comparisons

Equals Method

Value comparison

if (s1.Equals(s2)) //instance method

if (String.Equals(s1,s2)) //staticmethod

Compare Method

More comparison

Case-insensitive option Dictionary ordering

Locale-Specific Compare Options

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String Comparison Operators

The == and != Operators Are Overloaded forStrings

They Are Equivalent to String.Equals and !String.Equals

string a = Test ;string b = Test ;if ( a == b ) . // Returns true

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The Object Hierarchy

The Object Type

Common Methods

Reflection

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The object Type

Synonym for System.Object

Base Class for All Classes

SystemException

Exception

Object

MyClassString

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Common Methods

Common Methods for All Reference Types

ToString method

Equals method

GetType method Finalize method

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Reflection

You Can Query the Type of an Object

System.Reflection Namespace

The typeofOperator Returns a Type Object

Compile-time classes only GetType Method in System.Object

Run-time class information

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Namespace in the .NET Framework

System.IO Namespace

System.Xml Namespace

System.Data Namespace

Other Useful Namespace

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System.IO Namespace

Access to File System Input/Output

File, Directory

StreamReader, StreamWriter bytes,characters

FileStream random access to files

BinaryReader, BinaryWriter binary types

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System.Xml Namespace

XML Support

Various XML-Related Standards

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System.Data Namespace

System.Data.SqlClient

SQL Server .NET Data Provider

System.Data

Consists mostly of the classes thatconstitute the ADO.NET architecture

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Other Usefule Namespaces

System Namespace

System.Net Namespace

System.Net.Sockets Namespace

System.Windows.Forms Namespace

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Data Conversions

Converting Value Types

Parent/Child Conversions

The is Operator

The as Operator Conversions and the object Type

Conversions and Interfaces

Boxing and Unboxing

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Converting Value Types

Impilcit Conversions

Explicit Conversions

Cast operator

Exceptions System.Convert Class

Handles the conversions internally

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Reference Type Data Conversion

Parent - General

Child - Specific

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Parent/Child Conversions

Conversion to Parent Class Reference

Implicit or explicit

Always succeeds

Can always assign to object

Conversion to Child Class Reference

Explicit casting required

Will check that the reference is of the

correct type Will raise InvalidCastException if not

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The is Operator

Returns true If a Conversion Can Be Made

InvalidCastException

Bird b ;if ( a is Bird )

b = ( Bird ) a ; // Safeelse

Console.WriteLine (Not a Bird) ;

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The as Operator

Converts Between References Types, Like Cast

On Error

Returns null

Does not raise an exception

Bird b = a as Bird ;if ( b == null )

Console.WriteLine (Not a Bird) ;

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Conversions and the object Type

The object Type Is the Base for All Classes

Any Reflection Can Be Assigned to object

Any object Variable Can Be Assigned to AnyReference

With appropriate type conversion andchecks

The object Type and is Operator

object ox ;ox = a ;ox = (object) a ;ox = a as object ;

b = (Bird) ox ;b = ox as Bird ;

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Conversion and Interfaces

An Interface Can Only Be Used to Access ItsOwn Members

Other Methods and Variables of the Class AreNot Accessible Through the Interface

Rectangle r = new Rectangle ( ) ;r.Move ( ) ;r.Paint ( ) ;

IVisual v = ( IVisual ) r ;

v.Move ( ) ; //not validv.Paint ( ) ; // ok

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Boxing and Unboxing

Unified Type System

Boxing (implicit : always success)

Unboxing

Calling Object Methods on Value Types

p = ( int ) box ;int p = 123 ;object box ;box = p ;

123box

123

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Data Conversions

Value = Value implicit conversionexplicit conversion

Reference = Reference parent = child : implicit

child = parent : explicit

Reference = Value boxing

Value = Reference unboxing