java workshop july

8/7/2019 Java Workshop July

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FastTrack toJava

MohamedSanaulla

SunCampusAmbassador


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Essential

LearningClasses

eLanguage

Started


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WhatisJava?

WhydoweneedtolearnJava?

ToolsrequiredforlearningJava


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avaas rogramm ng anguage

SimpleObject Architectural

Portable Distributed

Performance

Multithreaded Robust Dynamic


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InterpretstheJavaByteCode

Base

for

the

Java

Platform

Canbeportedtoanyplatform(OS)


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Interface(APIs)

argeco ec ono rea yma e

softwarecomponentsthat

.

Itisgroupedintolibrariesof

relatedclassesandinterfaces;

theselibrariesareknownas

packages.


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WhydoweneedtolearnJava?


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editor

JavaLibraries,toolsandtheVirtual

NetBeans IDE

JavaSEDocumentation


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Learning

the

Language


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ar a es,Typesan

O erators


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Class NotHelloWorld

{publicstaticvoidmain(String[]args)

System.out.println(NotAHelloWorldProgram);}}

DemoUsingNotepad


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ProgramStructure

Class {

publicstaticvoidmain(String[]arguments)

{

}


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DataTypes

StronglyTypedLanguage

SizesofallNumerictypesareplatformindependent

, ,

and1booleanIntegers:

long 8bytes

int 4bytes

short 2bytesbyte 1byte

FloatingPoint:

double 8bytes Moreprecisionthanfloat

char 2bytesItisUnsigned,Accommodatesallcharactersusedin

a anguagesint ewor

boolean 2Values false ortrue


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Variables

execution

Declare Placingthetypefirstfollowedbythenameofvariable

Primitives

Once

Declared

Type

cannot

be

changed,

but

value

canReference Variables

Declarin :

int length,width,height;

boolean status;

CannotUseJavaKe Words asVariableNames mustnotbe inwithadi it

canbeofanylength,case issignificant

Initializing:CannotuseuninitializedLocalVariables

int length=23;

boolean status=true;Constants Declaredbyusingfinalkeyword Whichmeansvariablecannot

beassignednewvalue

finaldouble length=2.54;


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Methods

class MethodDemo

{

publicstaticvoidmain(String[]args)

showMessage(Sanaulla);

}

static void showMessage (Stringname)

{

System.out.println(Hi!!!+name);}


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InputandOutput

TakingInput:importjava.util.*;

Scannerin=newScanner System.in ;

in.nextInt(); //ForreadingInteger

in.nextDouble(); //ForReadingDouble

in.nextLine(); //ForReadingCompleteLine

Output:S stem.out. rintln Not Hello WorldSimilarto printf(NotHelloWorld\n);

. . Similarto printf(NotHelloWorld);


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Arrays

narray sanor ere co ec on a s ores manyelementsofthesametype withinonevariablename.

Elementsaretheitemsinanarray.

Eachelementisidentifiedwithanindexnumber.

Indexnumbersalwaysstartat0forthefirstelement.

Thelengthofanarrayisestablishedwhenthearrayis

created.Aftercreation,itslengthisfixed.


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DeclaringArray:

int[]key; //Arrayofints

Thread[]threads; //ArrayofObjectReferences

ConstructingArrays:

int[]key=newint[4];

MultidimensionalArrays:

int[][]myArray=newint[3][];

Declaring,Constructing,InitializingonOneLine:

int[]keys={5,6,7,8};

Str ng names= qwer , qweqe , g s ;

AnonymousArray:

int[]testScores;

testScores=newint[]{6,7,8};


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=


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BasicControlStructures

ifelseStructure

forloopandforeachloop

whileloop

switch statements

o

w e

oop


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ifElseStructure

{

int age;InputforAge

System.out.println(EntertheAgeoftheperson);Scanner in=newScanner(System.in);=k

if(age


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if(condition)

Statementstobeexecuted

elseif(condition)

Statementstobeexecuted

}

else

{Statementstobeexecuted

}


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OneCaution!!!!!!

YouWanttodothis:

if someBooleanVariable == true

{

Statements;

But

End

up

doing

this:some oo ean ar a e = rue

{

Statements;

}else

Statements;

}


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forloop

for int i=0 i


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for initialization termination increment

{

}

Demo

f


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SomeforLoopIssues:Noneofthethreesectionsofthefordeclarationarerequired

for(;;){

Statements;

}

Variablesdeclaredintheforstatementarelocaltotheforloopanc

cant

be

used

outside

the

scope

of

the

loop

for(int i=0;i


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foreachloop

AlsocalledastheEnhancedForloop,was

addedinJava5.Itsimplifieslooping

throughArraysandCollections.The

enhancedforLoophas twocomponents.

int[]

a

={1,2,3,4,5,6};

Declaration

for( int i : a) Expressions

System.out.println(i);


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Declaration

,

typecompatiblewiththeelementsofthe.

beavailablewithintheforblock,anditselement.


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This

mustevaluatetothearrayonewantstoloopthrough.Thiscouldbeanarrayvariableoramethodcallthatreturnsanarray.Thearraycanbeanytype:primitives,objects,evenarrays


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whileloop

int x=2;Expression

{ System.out.println(x);

++

}


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while (expression )

{

//Dostuff

}

Usedwhenthenumberofiterationsofthe

oc s a emen s

are

no

nown

Demo


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switchstatements

switch(expression)

case constant1:codeblockcase constant2:codeblock

}

Demo


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LegalExpressionsforswitch andcase:

Aswitchsexpressionmustevaluatetoachar,byte,

Acaseconstant mustevaluatetothesametypeas

theswitchexpression canuse

Thecaseconstantmustbecompiletimeconstants

Compiletimeconstanthastoberesolvedatcompile

t me,t atmeansonecanuseon yaconstantor na

variablethatisassignedaliteralvalue.

.

Itsalsoillegaltohavemorethanonecaselabel

usin thesamevalue

d hil L


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dowhileLoop

Thedoloopissimilartowhileloop,except

thattheexpressionisnotevaluateduntil

afterthedoloopscodeisexecuted.

Demo

OO Programming Concepts


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OOProgrammingConcepts

WhatisanObject?

WhatisaClass?

WhatisEncapsulation?

WhatisInheritance?

a s o ymorp sm

What is an Object?


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WhatisanObject?

consistsoftwocharacteristics:

1.State

2.Be avior

State >Depictedbymeansoffields

Behavior >Depictedbymeansofmethods

Advantages of Using Objects


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AdvantagesofUsingObjects

Modularity:Thesourcecodeforanobjectcan

be written and maintained inde endentl of the

source

code

for

other

objectsInformationHiding:UsingMethodsfor

interactingwillhidetheinternalimplementation

details

o e euse: eex s ng ec can ereuse

Pluggability anddebuggingease:Ifaparticular

corrected.SimilartoBoltinamachine

What is a class?


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Whatisaclass?

Aclass isageneralspecificationor

descriptionforasetofobjects that

definestheircommonstructure(data),

behavior (methods),andrelationships.

Objects

are

instances

of

Class

What is Inheritance?


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WhatisInheritance?

classisaparentofanother.

Implements isarelationshipbetweenobjects

Commona ityamongt eO jectsista enouttore uce

complexityProvidestheideaofreusability

What is Polymorphism?


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WhatisPolymorphism?

Abilitytotakemorethanoneforms

havingmethodswiththesamenamesand

dependingonthereceiver.

Wh t i E l ti ?


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WhatisEncapsulation?

Encapsulation referstomechanismsthatallow

eachobjecttohaveitsowndataandmethods

i.e.wrappingupofdataandmethodsintoa

singleunitcalledclass

accesstothemthroughaccessorandmutator

methods.

Accessor Methods: Accessor methodsreturn

informationMutator Methods:Mutator methodsmodify

es a eo eo ec .


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En o Sess on1


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Session2

MohamedSanaulla

SunCampusAmbassador


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Theofficialwebsite+mailing listofNITKSunClub

htt : rou s. oo le.com rou nitksunclub

SubscribetothisGooglegrouptoregisterforNITKSunClub!

Discussions

:Feelfreetopostanyqueries,ideas,newsyouhaveto

t ema ng st ta epart nt e scuss ons.

Files,Links,Resources:Findandshareallimportant, , ,

posters,brochures,etc relatedtotheclub'sactivities.

Events&Achievements:Gettoknowaboutallthelatesthappeningsandupcomingeventsoftheclub.


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Session1Contest

Winners!!!!

Mohit Kukre a

.


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O jectOrientationinJava

Classes


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InGeneralclassesinJavaaremadeu ofthree arts:

1. Fields Definethestate/attributesoftheClass

2. Constructors UsedforInitializingtheObjectsduring

3. Methods

Define

the

Behavior

of

a

particular

class,

alsousedforaccessingthefields

class

Fields

Constructor

Methods

}


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AClasscanbemarked

public default final abstract

Thedefaultaccesslevelcannotbymarkedbyusingdefaultkeyword.Itstheaccesslevelbydefault

Member Access Modifiers


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MemberAccessModifiers

,

protected,private,default

Public memberscanbeaccessedbyallotherclasses

Private memberscanbeaccessedbythecodeinthe

sameclass

Default memberscanbeaccessedonlybyclassesinthe

same acka e

Protected memberscanbeaccessedbyotherclassesin

thesamepackage,plussubclassesregardlessofthe

package.

Nonaccess Member Modifiers


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Nonaccess MemberModifiers

Final methods cannotbeoverriddeninasubclass

Abstract methods methodsdeclaredbutnot

Synchronized methods methodscanbeaccessedby

only

one

thread

at

a

timeTransient Variable ThevariableismarkedasTransient

isskippedduringserialization

o at e ar a e et rea access ngt evar a euses

itsownprivatecopy,withmastercopyinmemory

Constructors


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class andhasnoreturntype notevenvoid.

EveryclassMUST haveaconstructor BydefaultJavaprovides

NoArgConstructor.

Constructorscanuseany accessmodifiers

Everyconstructorhas,asitsfirststatement,eitheracalltoan

overloaded constructorortothesuperclass constructor.

Thecompilerbydefaultinsertanoarg calltosuper() asthevery

firststatementintheconstructor.

Interfaces donot haveConstructors

Objects


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Created b usin the new ke word

Theyliveontheheap areaofthememory

TheyareaccessedbyusingObject References that

veon es ac

MethodsandFieldsbyusingthe.operator


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StaticVariables

StaticMethods

StaticFields


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Definedbyusingthekeywordstatic.

Theresonlyonesuchfieldperclasswhich

.

Static

constants

are

more

popular

publicstaticfinalisusedtodefinea

constant.

StaticMethods


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haveathisparameter.

Cannotaccessinstancevariablesbutcan

accessonlystaticvariables.

Theyareaccessedbyusingthenameofthe

,

accessthestaticmethod.


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:

InitializationBlocks


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Apart romConstructorsan met o s, n t a zat on oc s aret eonlyplacewhereJavaoperationscanbeperformed.Therearetwo

typesofInitializationblocksinJava:

InstanceInitializationBlocks Theyrunonceeverytimethenew

.

StaticInitializationBlocks Theyrunonce,whentheclassisfirst

o a e . e ne yus ngt e eywor stat c .

SomeRulestoremember:

Init

Blocks

executeintheordertheyappear.StaticInitBlocksrunonce,whentheclassisfirstloaded.

InstanceInitblocksrunaftertheconstructorscalltosuper().


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DEMO:UsingInitializationBlocks

Methodoverloading


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Overloadedmethodsletsonetoreusethesamemethod

nameinaclass,butwithdifferentarguments.

TherulesforOverloadingare: .

OverloadedmethodsCANchangethereturntype.

Overloaded

methods

CAN

change

the

access

modifier.OverloadedmethodsCANdeclareneworbroader

checkedexceptions

DEMO:UsingOverloadedMethods

InnerClassesInner Class is a class defined inside another class


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InnerClassisaclassdefinedinsideanotherclass.

WhyuseInnerClasses?Canaccessthedatafromthescopeinwhichtheyaredefined

Canbehiddenfromtheclassesinthesamepackage

Reducetheamountofcodinginvolved

InnerClassescomein4flavors:

1. StaticMemberClasses Markedwithstatic,cannotaccessnonstatic

membersoftoplevelclass.,notaninnerclass TopLevelNestedclass

. ,

aninnerclassonehastohaveaninstanceofouterclassMyOuter.MyInner inner = (new MyOuter()).new MyInner();

3. Loca C asses De ine wit inamet o o t ec ass,on y ina an a stract

canbeapplied,localvariablescannotbeaccessed.

. ,

interface


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DEMO:UsingLocalClasses

Inheritance


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Inheritanceinjavaisdoneusingthekeyword

.

Aclassthatisderivedfromanotherclassiscalled

.

Theclassfromwhichthesubclassisderivedis

called

a

superclass.EveryClassextendsfromtheclassObject.

MultipleInheritance inJavaisnot possible,but

t ent eresanot erwayo o ng t.


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ISAandHASArelationship


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ISARelationshipisassociatedwith

Inheritance.SupposeMySubClass

extends/inheritsMySuperClass then

MySubClass ISAMySuperClass

HASARelationshipisbasedonUsage

ratherthaninheritance.SupposeclassA

HASAclassBifcodeinclassAhasareferencetoaninstanceofclassB.

MethodOverriding


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CanoverridethemethodinheritedfromtheSuper

Classunlessitismarkedfinal.

se to e ne e av orspec ctot esu c ass.

Theargumentlistmustexactlymatchthatofthe

Thereturntypemustbethesameasorasubtypeof

the

return

t e

declared

in

the

ori inal

overridden

method.

Accesslevelcantbemorerestrictive.

Staticmethodscantbeoverridden Theyare

actuallyhidden.

DEMO:UsingMethodOverriding


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InterfacesAninterface isareferencetype,similartoaclass,thatcancontain


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onlyconstants,methodsignatures,andnestedtypes.

The canbeim lemented unlikeconcreteclassesthatcanbe

extended

.

Allinterfacemethodsareimplicitlypublic andabstract.Onecanuse

anycombinationofpublic orabstract ornomodifiers.

Allvariabledefinedintheinterfacemustbe ublic,static andfinal.

Any

combination

of

public,

static,

final

or

no

modifiers

is

legal.

.

DEMO:

Using

Interfaces

GarbageCollection

u oma e emory anagemen e e e ec s a can e reac e


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u oma e emory anagemen e e e ec s a can ereac e

CanonlySuggestVMforGC

NoparticularGCAlgorithmcanbeknownforsure

ec smus ave ve,reac a ere erence

MakingObjectseligibleforGC:

Nulling aReference:

MyClass obj = new MyClass();

obj=null;

Reassiging ReferenceVariable:

MyClass obj1 = new MyClass();

MyClass obj2 = new MyClass();

obj1 = obj2;

IsolatingaReference IslandsofIsolation

ForcingGC Contradiction Cannotbeforcedbutsuggested

System.gc();

finalize() Runcodeb4GC,calledonlyonce inanObjectslifetime.

NumbersandStrings


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Numbers Strings

Strings


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Stringobjectsareimmutable butStringreferencevariables

arenot

StringclassisFinal Methodscantbeoverridden.

JVMfindsaStringliteral ItsaddedtoStringConstantPool

,

DEMO:UsingStrings

Numbers


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int,byte, float >Primitives,butJavaisOOLanguage

Wra ers are rovided for each rimitive which wra the

primitivesintoObjects

Why?

Classesprovideutilitymethodsforprimitives

Autoboxing >Automaticallyconvertsprimitive intowrapper

Objects andviceversa

Wrappers

are

equal

(equals())

>

Same

type

and

have

Same

value

. ,

underjava.lang.Number


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Insummary,theessentialmethodsignaturesforWrapper

primitivexxxValue() toconvertaWrappertoa

primitiveparseXxx (String)

Ex:

parseInt()

toconvertaStringtoaprimitive

WrappervalueOf(String) toconvertaStringtoaWrapper

Method

s=static

n=NFEexception Boolean Byte Character Double Float Integer Long Short

byteValue x x x x x x


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doubleValue x x x x x x

floatValue x x x x x x

longValue x x x x x x

shortValue x x x x x x

parseXxx s,n x x x x x x

parseXxx

(withradix)

s,n x x x x

valueOf s,n x x x x x x x

valueOf

with radix

s,n x x x x

toString x x x x x x x x

toString s x x x x x x x x

(primitive)

toString

(primitive,

radix)

s x x

PassingVariablesintoMethods


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Javaisalways PassbyValue

WhilepassingLocal Variables ItsresemblesPassby

Value

WhilepassingReferenceVariables ItsresemblesPass

ByReference,ButitspassbyValue

DEMO:PassingObjectReferenceVariables

DEMO:PassingLocalVariables

TheStringBuilder Class


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mutable i.e thevaluetheyarereferringtocanbechanged

ns anceso r ng u er areno sa e oruse ymu p e

threads i.e themethodsarenotsynchronized

StringBuilders simpler code andbetter performance

theStringinvolvesnewmemoryallocationandstringrelocation.

so r ng u er an r ng u er aresame r ng u er

wasintroducedinJDK5.0

DEMO:UsingStringBuilder


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UsingJDKDocumentation


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En o Sess on2


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Session3

MohamedSanaulla

SunCampusAmbassador

EssentialClasses


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ExceptionHandling

E ti h dli El t M h i f H dli


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Exceptionhandling >ElegantMechanismforHandling

Exception

Separates

Exception

Generating

and

Exception Handlingcodes

Exception Alters thenormal programflow.

try andcatch keywordsusedforExceptionHandling

Mechanism

try >DefiningBlock ofcodewhereexceptions canoccur

catch >DefiningBlock ofcodethathandles aspecific

exception

try

//Ri k C d G h h ki d f i


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//RiskyCodeGoesherethatcausessomekindofexception

}

catch(MyFirstException)

{

}

catch(MySecondException)

//HandlethisException

}

//NormalNonRiskycodecontinueshere

Usingfinally

Differentfromfinalize


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Different from finalize

Codeinsidethefinallyblockisexecutedatsomepointaftertry

block Whetheranexceptionisthrownornot

Iftheresareturnstatement Itsisexecutedimmediatelyafter

e re urn sencoun ere u e ore e re urn execu es.

IfNoExceptions Itisexecutedimmediatelyaftertry block

IftheresExceptions Itisexecutedafterthecatchblock

tr without acatch butwith finall isle al

try without acatch andalsofinally isillegal

try with catch andfinally islegal.

DEMO:UsingExceptionHandling

ExceptionHierarchy


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BasicI/O

Important I/O Classes:


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ImportantI/OClasses:File >Anabstractrepresentationsoffileanddirectory

pat name.

FileReader >UsedtoreadCharacterFiles

BufferedReader >WraparoundtheLowLevelreaders

ReducestheNoofReadOperations

e r ter > se towr tetoc aracter es.

Buffered Writer >Wraparoundthelowlevelwriters

import java.io.*; >Tobeused

UsingclassFile

A i f l Fil d


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AnewinstanceofclassFiledoesnotmean

,

name

DEMO

SomeMethodsUsed:

boolean exists()>returnstrueifitcanfind

theactualfile

UsingFileReader andFileWriter

> Most of the time they are used with wrapping them i e


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>Mostofthetimetheyareusedwithwrappingthemi.e

byusingitalongwithPrintWriter andPrintReader.Its

alsocalledaschaining

DEMO

DEMO:UsingPrintWriter

java.ioClass ExtendsFrom KeyConstructor(s)

Arguments

KeyMethods

File Object File,String createNewFile()

tr ng

String,String

e ete

exists()


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isDirectory()

isFile()

st

mkdir()

renameTo()

FileWriter Writer File close()

String flush()

write()

BufferedWriter Writer Writer close()

flush

newLine()

write()

PrintWriter Writer File(asofJava5) close()

OutputStream

Writer

format()*,printf()*

print(),println()

write()

e ea er ea er e

String

rea

BufferedReader Reader Reader read()

readLine()

Serialization

UsedforSavingtheState(InstanceVariables) ofoneormore


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Used for Saving the State (Instance Variables) ofone or moreObjects

Variablesmarkedtransientcannotbesavedduringobject

Serialization

BasicSerializationinvolvesonlytwomethods

Serializetheobjectsandwritethemtothestream

Readthestreamanddeserialize theobjects

.

ObjectOutputStream.readObject()

DEMO: UsingSerialization


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ObjectGraphs

Multithreading

InJava,threadmeans


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In Java, thread meansAninstanceofclass.java.lang.Thread

Athreadofexecution

Athreadofexecutionisanindividualprocessthathas

itsowncallstack.

JVMactslikeaminiOS >Schedulesitsownthreads

Theprogramsmustnotbedesigneddependenton

particularimplementationoftheJVM.

MakingaThread

ns anceo ava. ang. rea


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ImportantMethods:

start()

yield()

run()

u w

Thethreadofexecutionalwaysbeginswiththerun()

method

Extendthejava.lang.Thread class

ImplementtheRunnable Interface

DefiningaThread:

ByExtendingthejava.lang.Thread class:

l h d d h d


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class MyThread extends Thread

{

public void run()

{

System.out.println(Job Running inMyThread);

}

}

Thethreadwithrun methodwillbeexecutedasthestartin forthread.

Implementingjava.lang.Runnable:

{

public void run(){

. .

MyRunnable);

}

}

InstantiatingaThread:

ne as o ave rea o ec orun e rea egar esso su c ass ng or

implementing


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IftheThreadclassisextendedthen

MyThread t = new MyThread();

MyRunnable r = new MyRunnable();

Thread t =new Thread(r); //Passing Runnable to Thread

The samejobcanbegiventomultiplethreads

public class TestThreads

{

pu c s a c vo ma n r ng args

{

MyRunnable r =new MyRunnable();Thread foo = new Thread(r);

Thread bar= new Thread(r);

Thread bat = new Thread(r);

}

}

StartingaThread:

Tostartexecutingathread start()Methodisused


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g ()

t.start();

Aftercallingstart():

AnewThreadofexecutionstarts

ThreadmovesfromnewstatetoRunnable state

run()methodisreadytorun

DEMO:StartingandrunningaThread


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StartingandRunningMultipleThreads:


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DEMO:Startin andRunnin Multi leThreads

The order threads executin cannot be uaranteed The onl

Guaranteedthingis

Eachthreadwillstartandeachthreadwillrunto

ThreadStates

TheDifferentthreadstatesare:New


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New

Running

Waiting/blocked/sleeping

SunClub NITK


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http://groups.google.com/group/nitksunclub

OfficialBlog:

http://sunclubatnitk.wordpress.com/

MyJavaBlog:

. .

Theofficialwebsite+mailing listofNITKSunClub


110/113

htt : rou s. oo le.com rou nitksunclub

SubscribetothisGooglegrouptoregisterforNITKSunClub!

Discussions:Feelfreetopostanyqueries,ideas,newsyouhaveto

t ema ng st ta epart nt e scuss ons.

Files,Links,Resources:Findandshareallimportant, , ,

posters,brochures,etc relatedtotheclub'sactivities.

Events&Achievements:Gettoknowaboutallthelatesthappeningsandupcomingeventsoftheclub.


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java workshop july

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