PJ_M01_C01_PPT_Introduction to Object Oriented Programming Using Java.pdf

java unit 1

1. Introduction to
Object Oriented
Programming using
Java
Chapter 1.1

2. ToprovidestudentswiththebasicsofObject
OrientedProgrammingusingJava..
Aim

3. After completing this chapter, you should be able to:
•Explain the Object Oriented features in Java
•Describe the role of JVM
•Illustrate keywords, variables and data types in Java
•Demonstrate common lexical issues in Java
•Illustrate Java type conversion and casting
•Describe arrays in Java
Instructional Objectives

4. LearningOutcomes
Attheendofthischapter,youareexpectedto:
•DifferentiatebetweenthefeaturesofC++andJava.
•Applyvariousdatatypes,keywordsandvariablesinasimpleJava
program.
•DemonstratecommonlexicalissuesbycreatingaprograminJavato
countthenumberofspaces,identifiersandcomments.
•Describethetypesoftypeconversionwithexamples.
•Createaprogramtoillustratetheconceptofpassinganarraytomethod.
•Demonstratetheapplicationsofmultidimensionalarraywithan
example.

5. Introduction to Object Oriented
Programming in Java

6. I.ObjectOrientedProgramminginJava
Introduction
Oneofthemostimportantconceptsof
programminglanguageisitsreliability.Object
OrientedProgrammingconcepthelpskeepinga
programminglanguagetoutmostreliableand
dependable.Let’slookdownuponhistoryofJavaand
howdoesitcometoexistenceasaprogramming
languageafterCandC++.

7. ObjectOrientedProgramminginJava
EvolutionofJava
Researcherswerethinkingofaprogramminglanguagewhichcouldbesecurable,
reusableandsupportallplatformsandalsoactsasaclass-based,object-oriented
withspecificallydesigneddependenciestofixthedrawbacksofexistinglanguages
likeCandC++.WhereCisnotsecured,andC++doesnothavetheadvanced
characteristic.
Itintendedtodevelopanapplicationprogramwhichcanbe"writeonceandrun
anywhere"(WORA),whichmeansthecompiledJavacodecanrunonallplatforms
thatsupportJava.

8. ObjectOrientedProgramminginJava
HistoryofJava
ThemostpopularprogramminglanguagesareC,C++,C#,andJava.WhereJavaisanadvanced
programminglanguageandfacilitatesadvancedtechnicalfeatureswhencomparedwitheach
other.
Arevolutionarytasktodevelopaprogramfordigitaldevicessuchassettopboxesandtelevision
wasaninterestingfactwhichmadeJavaprogrammingtocomeintoexistence.Itwasanadvance
conceptatthattimeforGreenteammembers(developersofJavaprogrammers)butitsatisfied
thedemandsofinternetprogramming.Later,NetscapeincorporatedJavaprogramming.
Javaisapropertiedlanguagewhichhasitsbestelementstoinheritandcombinewithany
innovativeconceptwhichcanbuilditsownuniquemission.Javaisatechnicallyblendedlanguage
whichhasarichelementsthatcanaddressanychangingexpectationsandtechnicalinnovations.
Atpresent,Javaisoneofthemostpopularprogramminginuse,particularlyinclient-server
architecture,internetprogramming,mobiledevices,games,e-businesssolutionsetc.

9. ObjectOrientedProgramminginJava
Object Oriented Programming Concepts
JavaisanObjectOrientedlanguage.ItprovidesthefeaturetoimplementanObject
Orientedmodel,whereitisorganisedaroundobjectsandlogicratherthandata.It
isusedinthebeginningofsoftwarelifecycleandalsousedtodevelopother
applications.
ObjectOrientedProgrammingisatechniqueinwhichprogramsarewrittenonthe
basisofobjectse.g.(Java)whereitadoptsaconceptthatviewseverythingasan
objectandimplementsalogicinrelationtoit.Let’sseetheconceptsofObject
OrientedProgrammingindetailwithanrealtimeexample.

10. Object Oriented Programming
Concepts

11. Object Oriented Programming Concepts
Object
Anobjectisnothingbutamatterofthing
whatwefindineverydaylife.Technically,
Javaisasoftwarebundleofrelatedstateand
behaviour.
Example:Car,box,mountain,computeretc.

12. Object Oriented Programming Concepts
Object and its components

13. Object Oriented Programming Concepts
Object with Its Attributes

14. Object Oriented Programming Concepts
Class
InJavaprogramming,classisdefinedas
ablueprintfromwhichobjectsare
created.Itmodelsanddescribesthe
stateandbehaviourofanobject.
Example:Consideracarwithseveral
propertieslikeclutch,steering,break,
etc.

15. Object Oriented Programming Concepts
Inheritance
Inheritanceisapropertybywhichstateand
behaviourofoneclass(superclass)canbe
inheritedtoitssub-class.Itisapowerful
andanaturalmechanismfororganisingand
structuringasoftware.
Example:Humanheredity

16. Object Oriented Programming Concepts
Abstraction
Hidingtheimplementationdetailsfromtheuseriscalledasabstraction.Here,
onlythefunctionalitywillbeprovided.InJava,abstractioncanbeachievedby
abstractclass,andInterface.
Aclasswithanabstractkeywordiscalledasabstraction.
Interface–blueprintofaclass.Fullabstractioncanbeachievedusingthis
mechanism.
Example:Inventionofflightisbasedontheflyingmechanismlearntfrom
birds.Soflightsarederivedformbaseclassbirds.

17. Object Oriented Programming Concepts
Encapsulation
EncapsulationisoneofthefundamentalconceptofOOP.
Mechanismofbindingthedataandfunctiontogetherinasingle
unitiscalledasencapsulation.

18. Object Oriented Programming Concepts
Polymorphism
Polymorphismisanabilityofanobjecttotakemanyforms.Itreacts
differentlyindifferentsituation.InJava,polymorphismisusedtoreduce
codecomplexities.Methodsorfunctionofaclassimpliesthebehaviourof
polymorphism.InJava,allJavaobjectsarepolymorphic.

19. Components of Java

20. Components of Java
JavaCompiler
Compilerisusedtosystemizetheprogramandcheckagainstlanguagesyntax
rules.Itconvertsthesourcecodetobytecodeandthencompilesthem.TheJava
compilergeneratesanarchitecture-neutralobjectfileformat(thecompiledcode–
sourcecodeandbytecode)tobeexecutableonmanyprocessors.
Sourcecode-collectionofcomputerinstructionswritteninhumanreadableformat.
Writestheoutputinjavafile
Bytecode-computerobjectcode,alsocalledasinstructionsetofJavaVirtualMachine.
Writestheoutputinclassfile

21. Java Virtual Machine (JVM)
JavaVirtualMachine–enablesthecomputertorunJavaprogram.Itreadsandinterprets
classfilesandexecutestheprogram’sinstructionintonativehardwareplatform.
JVMisplatformindependent(obtainableformanyhardwareandsoftwareplatforms).In
theJavavirtualmachinespecification,thebehaviourofavirtualmachineinstanceis
describedintermsofsubsystems,memoryareas,datatypes,andinstructions.These
componentsdescribeanabstractinnerarchitecturefortheabstractJavavirtualmachine.
Thepurposeofthesecomponentsisnotsomuchtodictateaninnerarchitecturefor
implementations.Itismoretoprovideawaytostrictlydefinetheexternalbehaviourof
implementations.ThespecificationdefinestherequiredbehaviourofanyJavavirtual
machineimplementationintermsoftheseabstractcomponentsandtheirinteractions.

22. Java Virtual Machine (JVM)
Let’sdiscusswhatdoesJVMperforms?
Itisusedtoloadthecode
ItVerifiesandexecutesthecode
Anditprovidesruntimeenvironment

23. Java Virtual Machine (JVM)

24. Java Virtual Machine (JVM)
Components of JVM:
Following are the components of JVM:
•Stack
•Heap
•Constant Pool
•Code segment
•Program counter

25. Components Of JVM
1.Stack
Temporaryvaluesarestoredinframesofa
stack.
ItcontainsthestateofJavamethodinvocation.
Whileinvokingamethod,JVMpushesanew
frameontothatthread’sJavastack.
Aftercompletionofasinglemethod,thevirtual
machinepopsanddiscardstheframeforthat
method.

26. Components Of JVM
Heap
Heap consists of objects. The JVM has a
heapthat is the runtime data area from which
memory for all class instances and arrays are
allocated.
It is created at the JVM start-up.
•Heap Memory –store Java objects
•Non-heap memory –Store Meta data and
other loaded classes.

27. Components Of JVM
Constant Pool
Constant pool consist of all constant data.
They comprise of
•Numbers
•Strings
•Symbolic names of classes, interfaces
and fields

28. Components Of JVM
Program Counter
Tracking of current instruction execution at any
moment is done by Program Counter (PC) register.
It is similar to that of pointer which keeps in track of
current instruction in sequence.
Every time a new thread is created, a PC register is
also created simultaneously.
PC keeps a pointer to the current statement that is
being executed in its thread.

29. 29
Simple Java Program
•Javaisageneral-purposeprogramminglanguage.Likeanyprogramming
language,Javaalsohasitsownsyntax,structureandprogrammingparadigmto
buildarobust,reusableandmaintainableapplicationsprograms.
•JavaprogramsareexecutedinitsdevelopmentenvironmentsuchasJava
DevelopmentKit(JDK)andEclipseIDE.
•Programmatically,JavaisaderivativeofC++language.SyntaxofJavalookssimilar
likeC.Codeblocksaremodularisedintomethodsanddelimitedbybraces({})
andvariablesaredeclaredbeforetheyareused.
•Javaprogramstartswithapackagewherethepackagecanbedefinedasa
namespacemechanism.Ithelpstomaintainthehierarchicalfilesystem,manage
filesystemandclasssystem.

30. Hierarchy of Java Program Components

31. Java Program
Example : A simple java program is illustrated below :
public class FirstProgram
{
Public static void main (string [ ]args)
{
Sytem.out.println(“ First Java Program”);
} //end of main
} //end of First Program class

32. Self –Assessment Questions
1)Java is an architectural dependent programming language.
a)True b) False
2) ______________ is an instance of class.
a)Package b) Object
c)Class d) None of these
3) By default, all Java Objects are Polymorphic.
a) True b) False

33. Data types, Keywords and Variables

34. II. Data Types, Keyword and Variables
Variablesarememorylocationstostorevalues.
Whenausercreatesavariable,amemoryspaceisreservedforthatthevariable.
Basedonthetypeofthevariable,theoperatingsystemallocatesmemoryand
decideswhatcanbestoredinthatreservedspace.
Ausercanstoreintegers,decimals,character,etc.byassigningdifferentdata
typestothevariables.
Datatypeisakeywordusedtoallocatesufficientmemoryspaceforthedata.
Pictorialrepresentationofdatatypesanditsclassificationsaregivenbelow:

35. Classification of Data types

36. Classification of Data types
Let’sseethelistofdatatypesanditsdescriptioninthefollowing.Thetypes
are:
•Integer
•Floatingpoint
•Character
•Boolean
•TypeconversionandCasting
•AutomaticTypepromotioninexpression

37. Integers

38. Integers
Java defines four integer types:
Byteshort
int long
Allofthesearesigned,positiveandnegativevalues.
Javadoesnotsupportunsigneddatatypes.Whereas
signedandunsignedintegersaresupportedbymany
othercomputerlanguages.
Javadesignersfeltthatunsignedintegersare
unnecessarybecausetheyaremostlyusedtospecify
behaviorofthehigherorderbit,whichdefinesthe
signofanintegervalue.Thewidthofanintegertype
shouldnotbethoughtofastheamountofstorageit
consumes,butratherasthebehavioritdefinesfor
variablesandexpressionsofthattype.TheJavarun-
timeenvironmentisfreetousewhateversizeitwants,
aslongasthetypesbehaveasyoudeclaredthem.

39. Integers
Integers and its types
Name Width Range
Long
64 -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
Int
32 -2,147,483,648 to 2,147,483,647
Short
16 -32,768 to 32,768
Byte
8 -128 to 127

40. Bytes
•Thesmallestintegertypeisbyte.
•Thisisasigned8-bittypethathasarangefrom-128to127.
•Variablesoftypebyteareespeciallyusefulwhenyou’reworkingwitha
streamofdatafromanetworkorfile.
Itcanberepresentedas:
Byteb,c;

41. Short
•Shortisasigned16-bittype.
•Ithasarangefrom–32,768to32,767.
•Itisprobablytheleast-usedJavatype.
Herearesomeexamplesofshortvariabledeclarations:
short s;
short t;

42. Int
•Themostcommonlyusedintegertypeisint.
•Itisasigned32-bittypethathasarangefrom–2,147,483,648to
2,147,483,647.
•Inadditiontootheruses,variablesoftypeintarecommonlyemployedto
controlloopsandtoindexarrays.

43. Long
•Longisasigned64-bittypeandisusefulforthoseoccasionswhereanint
typeisnotlargeenoughtoholdthedesiredvalue.
•Therangeofalongisquitelarge.Thismakesitusefulwhenbig,whole
numbersareneeded.

44. Floating –Point
•Floating-pointnumbers,alsoknownasrealnumbers
•Therearetwokindsoffloating-pointtypes:
Float
Double
which represent single-and double-precision numbers, respectively.

45. Floating Point

46. Floating –Point types
Their Width and ranges are shown below :
Name Width Approximate Range
double 64 4.9e-324 to 1.8e+308
float 32 1.4e-0.45 to 3.4e+0.38

47. Floating –Point types
Float
•Floatisspecifiedasasingle-precisionvaluethatuses32bitsofstorage.
•Singleprecisionisfasterandtakeshalfasmuchspaceasdoubleprecision,,but
willbecomeimprecisewhenthevaluesareeitherverylargeorverysmall.
Here are some example float variable declarations:
float hightemp, lowtemp;

48. Floating –Point types
Double
•Doubleisdenotedbythekeyword‘double’whichisusedtostoreavalueof64bit.Itis
fasterthansingleprecisiononmodernprocessorthathavebeenoptimizedforhigh-
speedmathematicalcalculations.Someimportanceofdoubleare:
•Alltranscendentalmathfunctions,suchas
sin()
cos()
sqrt()
•returndoublevalues.
•Doubleisbestchoice,whenyouneedtomaintainaccuracyovermanyiterative
calculations,oraremanipulatinglarge-valuednumbers.

49. Example Programs

50. Integer
Public class DataType_int
{
inta=100;
intb=-150;
void add( )
{
Intc=a + b;
Sysytem.out.println(“The int
value is:” +c);
}
}
Class Demo
{
public static void main(String
args[ ] )
{
Datatype_Intobj=new
DataType_Int( );
Obj.add();
}
}
Output:
The intvalue is -50

51. Double Integer
//Computetheareaofacircle.
classArea{
publicstaticvoidmain(Stringargs[])
{doublepi,r,a;
r=10.8;//radiusofcircle
pi=3.1416;//pi,approximately
a=pi*r*r;//computearea
System.out.println("Areaofcircleis"+a);
}
}
Output:
Area of circle is 366.435

52. Characters

53. Characters
•charinJavaisnotthesameascharinCorC++.
•JavausesUnicodetorepresentcharacters.
•Unicodedefinesafullyinternationalcharactersetthatcanrepresentallofthe
charactersfoundinallhumanlanguages.
•Itisaunificationofdozensofcharactersets,suchas
Latin
Greek
Arabic
Cyrillic
Hebrew

54. Characters
•InJava,charis16bitandrangesfrom0to65,536.
•Therearenonegativechars.
•ThestandardsetofcharactersknownasASCIIstillrangesfrom0to127as
always,andtheextended8-bitcharacterset,ISO-Latin-1,rangesfrom0to255.

55. Characters
Example Program : Demonstrates char variables
class CharDemo{
public static void main(String args[]) {
char ch1, ch2;
ch1 = 88; // code for X
ch2 = 'Y';
System.out.print("ch1 and ch2: ");
System.out.println(ch1 + " " + ch2);
}
}
This program displays the following output:
ch1 and ch2: X Y

56. Boolean

57. Boolean
TheBooleanlogicaloperatorsare:
|,&,^,!,||,&&,==,!=.
•JavasuppliesaprimitivedatatypecalledBoolean,instancesofwhichcantake
thevaluetrueorfalseonly,andhavethedefaultvaluefalse.
•ThemajoruseofBooleanfacilitiesistoimplementtheexpressionswhich
controlifdecisionsandwhileloops.

58. Boolean
Example program:
class Boolean
{
public static void main(String args[])
{
// these are booleanvariables
booleanA = true;
booleanB = false;
System.out.println("A|B = "+(A|B));
System.out.println("A&B = "+(A&B)); // program execution using boolean
System.out.println("!A = "+(!A));
System.out.println("A^B = "+(A^B));
System.out.println("(A|B)&A = "+((A|B)&A));
}
}
Syntax:
booleanValue(); // returns the value of Boolean object

59. TypeCastingandConversion

60. Type conversion and Casting
•Typecastingisusedtoassignvalueofonetypeofavariabletoanothertype.
Castinginotherwordsisaninstructiontothecompilertoconvertonetypeto
another.
•IthelpsJavanotonlytoperformonlyarithmeticoperationsonpairsofvaluesof
sametypebutperformsoperationsonmixedtypetoo.
•Forexamplethevalueoftherightsideisautomaticallyconvertedtothetypeof
theleftsideincompatibletypes.
•InJava,Booleanandintarenotcompatible.
•Whentheabovesaidconditionsaremet,awideningconversiontakesplace.

61. Type conversion and Casting
Types : There are two types
Types Casting
Widening casting Narrowing Casting

62. Type conversion and Casting
1) Widening casting
In widening casting, the value types are not directly expressed. Here, integer and
floating are compatible with each other. Integer literal can be assigned to char.
Widening
Byte Short Int Long Float Double

63. Type conversion and Casting
2) Narrow casting:
In narrow casting, the value types are directly expressed.
Narrowing
Double Float Long Int Short Byte

64. Type conversion and Casting
Difference between Widening and Narrowing
Widening Casting Narrowing Casting
Used to access new methods of child class or
while referring super class to child class
Used to access redefined class of parent class in the child class

65. Type conversion and Casting
Sample Program:
Package conversion;
Public class main
{
Public Static Void main(string [ ] args)
{
intvar1=12;
double var2=15.2;
double result = var1+var2;
System.Out.Println(“The sum is” + result)
}
}

66. Self –Assessment Questions
1) Boolean is used to control the decisional statement in a program
a)True b) False
2) Java supplies a primitive data type called_________________.
a)Integer b) Float
c)Boolean d) Character
3) Any size of an integer is handled by Java.
a) True b) False

67. LexicalIssues

68. Lexical Issues
•Javaprogramsarethecollectionofwhitespace,identifiers,literals,comments
andseparators.
•Lexicalissuesareverycommoninprogramming,whichisusedtoanalysis,
operateandimplementtheprograminasequentialorder.

69. Lexical Issues
Letusseethedetaildescriptionoflexicalissuesinthefollowing.
i.Whitespace
•Aswordbyitself,awhitespaceisnothingbutaspace,tab,oranewline.
•Javaisacasesensitivefree-formlanguagewhichmeansauserneednotfollow
anyspecialrules.
•Forexample,thereisnoformattobefollowedtowriteaJavaprogram.
•Aprogramcanbewritteneveninasinglelineoranynumberoflinescanbe
used,whateveruserwishes.
•Bydefault,singlewhitespaceisrequiredbetweeneachcharacter.

70. Lexical Issues
Identifiers
•Anidentifiercanbedescribedasanydescriptivesequenceofuppercase,
lowercaseletters,underscoreoradollar-signcharacter.
•Identifiersareusedforspecifyingclassname,methodnameandvariablename.
SinceJavaiscase-sensitivelanguageanyletterofawordwillbedifferentfromthe
otherformofthesimilarword.
•LetussayinJava,awordmaxisdifferentfromMAX.

71. Lexical Issues
Literals
Literalsareusedtospecifyadefaultvalueortodeclareaconstantvalue.
Itcanbea:
•Boolean–TrueorFalse
•Numeric–floating,decimal,integerorafixedpoint
•Characterbased–singlecharacterorastring

72. Lexical Issues
Comments
Three types of comments are supported by Java. They are
Comment Description
/*text*/ Compiler ignores everything from /* to */
//text Compiler ignores everything from // to the end
of the line
//**documentation*/ Called as doc comment (documentation
comment) –used by automatically generated
document

73. Lexical Issues
Separators
Separators are characters used to terminate statements. Commonly used separators
are semicolon (;). Following are few separators used in Java programs
Symbol Name Purpose
( ) Parenthesis Control the order of operation
{ } Braces Used to group statements and
declaration
[ ] Brackets Used to declare array types and
dereferencing array values
; semicolon Terminates statement
, comma Separates consecutive identifiers in a
variable decalaration

74. Self –Assessment Questions
1)____________line space is required to separate each statement.
a)Single b) Double
c) More than one d) Not required
2) Java is a case-sensitive programming language.
a)True b) False
3) _______ is used to store values specified by a data type.
a) Variables b) Identifiers
c) Literals d) Separators

75. Arrays

76. Arrays
Arrayisacollectionofsimilartypesofelementsthathavecontiguousmemorylocation.
Itisacontainerobjectthatholdsvaluesofhomogeneoustype.Javaarrayiscontainerobjectthat
containselementsofsimilardatatype.
Itcanhave:Onlyfixedsetofelementswhichcanbestoredinit.
Alsohavelabelasstaticdatastructurebecauseduringthetimeofdeclarationonlythesizeofthe
arrayisspecified.Anarraycontainingnumberofvariablesanditcanevenstartfromzero–whichis
calledasanempty,insteadtheyarereferencedbyarrayaccessexpressionsthatusenon-negative
integerindexvalues.
Syntax:
datatype[]identifier;Ordatatypeidentifier;

77. Arrays
Initialization of an array:
[ ] -Intoperator is used to initialize an array.
Example program:
Int[] arr= new int[15]; // 15 is the size of an array

78. Array
Array Type :
Arraytypesareusedindeclarationsandincastexpression.Anarraytypeiswrittenasthenameof
anelementtypefollowedbysomenumberofemptypairsofsquarebrackets[].Thenumberof
bracketpairsindicatesthedepthofarraynesting.
Anarray'slengthisnotpartofitstype.Itmaybeofanytype,whetherprimitiveorreference.
•Arrayswithaninterfacetypeastheelementtypeareallowed.Anelementofsuchanarray
mayhaveasitsvalueanullreferenceoraninstanceofanytypethatimplementstheinterface.
•Anarraywithanabstractclasstypeastheelementtypeareallowed.Anelementofsuchan
arraymayhaveasitsvalueanullreferenceoraninstanceofanysubclassoftheabstractclass
thatisnotitselfabstract.

79. Array
Array Variable:
A variable of an array type enfolds a reference to an object. It is used to create a
variable and does not create any space to that specified variable. Some of the
variable declarations are listed below. They are:
Declaration Comment
Int[ ] Array of int
Short [ ] [ ] Array of short
Object [ ] Array of object
Collection<?> Array of collection of unknown types

80. Array
SingleDimensionalArray:
Aone-dimensionalarrayconsistofalistoflike-typedvariables.
Thegeneralformofaone-dimensionalarraydeclarationis
Thegeneralformofnewasitappliestoone-dimensionalarrays,appearsas
follows:
arrayRefVar=newdataType[arraySize];
type var-name[ ]; // syntax

81. Array
Theabovestatementdoestwothings:
1.ItcreatesanarrayusingnewdataType[arraySize];
2.ItassignsthereferenceofthenewlycreatedarraytothevariablearrayRefVar.
Theexamplebelowallocatesa12-elementarrayofintegersandlinksthemto
month_days.
month_days=newint[12];
Afterthisstatementexecutes,month_dayswillrefertoanarrayof12integers.
Further,allelementsinthearraywillbeinitializedtozero.

82. Array
Youcanaccessaspecificelementinthearray,onceafteryouallocateanarrayby
Specifyingitsindexwithinsquarebrackets.Allarrayindexesstartatzero.
Forexample,thisstatementassignsthevalue28tothesecondelementof
month_days.
month_days[1]=28;
Thenextlinedisplaysthevaluestoredatindex3.
System.out.println(month_days[3]);

83. Array
Puttingtogetherallthepieces,hereisaprogramthatcreatesanarrayofthe
numberofdaysineachmonth.
// Demonstrate a one-dimensional
array.
class Array {
public static void main(String
args[]) {
intmonth_days[];
month_days= new int[12];
month_days[0] = 31;
month_days[1] = 28;
month_days[2] = 31;
month_days[3] = 30;
month_days[4] = 31;
month_days[5] = 30;
month_days[6] = 31;
month_days[7] = 31;
month_days[8] = 30;
month_days[9] = 31;
month_days[10] = 30;
month_days[11] = 31;
System.out.println("April has " +
month_days[3] + " days.");
}
}

84. Array
Whenyourunthisprogram,itprintsthenumberofdaysinApril.Asmentioned,
Javaarrayindexesstartwithzero,sothenumberofdaysinAprilis
month_days[3]or30.
Itispossibletocombinethedeclarationofthearrayvariablewiththeallocation
ofthearrayitself,asshownhere:

85. Array
MultidimensionalArray
Javadoesnotsupportmultidimensionalarrays.However,youcandeclareand
createanarrayofarrays
However,asyouwillsee,thereareacoupleofsubtledifferences.Todeclarea
multidimensionalarrayvariable,specifyeachadditionalindexusinganothersetof
squarebrackets.Forexample,thefollowingdeclaresatwodimensionalarray
variablecalledtwoD.
inttwoD[][]=newint[4][5];

86. // Demonstrate a two-dimensional array.
class TwoDArray{
public static void main(String args[]) {
inttwoD[ ] [ ]= new int[4][5];
inti, j, k = 0;
for(i=0; i<4; i++)
for(j=0; j<5; j++) {
twoD[i][j] = k;
k++;
}
for(i=0; i<4; i++) {
for(j=0; j<5; j++)
System.out.print(twoD[i][j] + " ");
System.out.println();
}}}
This program generates the
following output:
0 1 2 3 4
5 6 7 8 9
10 11 12 13 14
15 16 17 18 19
Thefollowingprogramnumberseachelementinthearrayfromlefttoright,topto
bottom,andthendisplaysthesevalues:

87. Summary
JavaisanObjectOrientedProgrammingLanguage.
Javaisatechnicallyblendedlanguagewhichhasarichelementsthatcanaddressanychanging
expectations.
Javaadoptsaconceptthatviewsverythingasanobjectandplacesanextraordinarydemands
ontheprograms.
Variablesarememorylocationstostorevalues.
Aclassisdefinedasblueprintfromwhichobjectsarecreated.
Castingisaninstructiontothecompilertoconvertonetypetoanother.
Separatorsarecharactersusedtoterminatestatements.
Arrayisacollectionofsimilartypesofelementsthathavecontiguousmemorylocation.
Javadoesnotsupportmulti-dimensionalarray

88. SubjectiveQuestions
1.Explainvariousdatatypes,keywordsandvariableswithan
exampleJavaprogram
2.WhatisanarrayinJava?Explainitstypeswithanexample.
3.Whatarelexicalissuesandexplainhowdoesithelpin
programimplementation?

89. •Brief description of activity
Activity
•Do an online study and prepare a presentation of
10-15 slides which describes the evolution of Java
from C++.
•You are required to:
•Differentiate between C++ and Java and list down
the secure features of Java when compared to C++.
•Pen down the strategies used in Java to make it
reliable and robust with a real time example.
Online Activity
(30 min)

90. •ThecompletereferenceJava-2:HerbertSchildt-5
th
edition-McGraw
Hillprofessional
•SAMSteachyourselfJava-2-RogersCedenheadandLeuraLemay-3
rd
edition–Pearson
e-References