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JavaThroughExamples
JavaThroughExamples i
Contents
1 Introduction 1
1.1 Instructor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Introductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Hands-OnLearning . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 HistoryofJava 1
2.1 JavaVersions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.2 SupportedPlatforms . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.3 WhyJava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3 Installation 3
3.1 InstallingJava . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2 InstallingEclipse . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4 Basics 4
4.1 HelloWorld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2 HelloWorldEclipse . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3 EclipseViews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.4 Projects, Packages, Classes . . . . . . . . . . . . . . . . . . . . . . 7
4.5 ProgramStructure . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.6 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Eclipse 10
5.1 Renaming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2 Exporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
JavaThroughExamples ii
6 PrimitiveDataTypes 12
6.1 IntegersandFloating-PointNumbers . . . . . . . . . . . . . . . . . 12
6.2 Variables, Types, Assignment . . . . . . . . . . . . . . . . . . . . . 12
6.3 NamingConventions . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.4 PrintfandFormat . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.5 NumericOperators . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.6 AssignmentOperators . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.7 Increment/DecrementOperators . . . . . . . . . . . . . . . . . . . 18
6.8 BitOperators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7 Strings 20
7.1 StringLiterals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.2 StringAssignmentOperator . . . . . . . . . . . . . . . . . . . . . . 21
7.3 EscapeSequences . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.4 ConvertingBetweenStringsandNumbers . . . . . . . . . . . . . . . 22
7.5 TipCalculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.6 PopulationCalculator . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.7 HousePrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8 Branching 25
8.1 If, If-Else . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.2 RelationalOperators . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.3 Booleans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.4 BooleanOperators . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.5 StringComparisonandEquality . . . . . . . . . . . . . . . . . . . . 29
8.6 TernaryOperator . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.7 Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.8 OperatorPrecedence . . . . . . . . . . . . . . . . . . . . . . . . . 33
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9 Looping 34
9.1 LoopingwithWhile . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.2 Break, Continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
9.3 LoopingwithFor . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.4 NestedLoops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.5 LoopingwithDo-While . . . . . . . . . . . . . . . . . . . . . . . . 39
10 StringsandCharacters 40
10.1 CharacterLiterals . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
10.2 AccessingStringCharacters . . . . . . . . . . . . . . . . . . . . . . 41
11 ConstantsandStaticMethods 42
11.1 Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
11.2 StaticFields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
11.3 StaticMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
11.4 Overloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
11.5 Visiblity, Namespaces, Import . . . . . . . . . . . . . . . . . . . . . 45
12 FileI/O 46
12.1 ReadFiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
12.2 WritingFiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
12.3 AppendingtoFiles . . . . . . . . . . . . . . . . . . . . . . . . . . 47
13 ObjectsandClasses 47
13.1 ObjectsandClasses . . . . . . . . . . . . . . . . . . . . . . . . . . 47
13.2 DefiningandUsingObjects . . . . . . . . . . . . . . . . . . . . . . 47
13.3 ObjectsversusStaticMethods . . . . . . . . . . . . . . . . . . . . . 49
13.4 Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
13.5 Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
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13.6 In-MemoryFile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
13.7 AnonymousClasses . . . . . . . . . . . . . . . . . . . . . . . . . . 51
13.8 Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
13.9 EnumTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
13.10NestedClasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
14 Exceptions 55
14.1 CatchingExceptions . . . . . . . . . . . . . . . . . . . . . . . . . . 55
14.2 ThrowingExceptions . . . . . . . . . . . . . . . . . . . . . . . . . 56
14.3 Finally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
15 Arrays 58
15.1 ArrayLiterals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
15.2 LoopingthroughArrays . . . . . . . . . . . . . . . . . . . . . . . . 58
16 Collections 60
16.1 Collections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
16.2 Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
16.3 ListMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
16.4 PrimitiveCollections . . . . . . . . . . . . . . . . . . . . . . . . . 62
16.5 WrapperObjects . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
16.6 Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
16.7 MapMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
16.8 MapTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
16.9 Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
16.10SetMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
16.11SetTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
JavaThroughExamples v
17 RegularExpressions 68
17.1 RegularExpressions . . . . . . . . . . . . . . . . . . . . . . . . . . 68
17.2 PatternMatching . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
17.3 RegexSummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
17.4 Replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
17.5 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
18 SystemInteraction 72
18.1 CommandLineArguments . . . . . . . . . . . . . . . . . . . . . . 72
18.2 CapturingCommandOutput . . . . . . . . . . . . . . . . . . . . . 72
19 MoreEclipse 73
19.1 AddingThirdPartyJarFiles . . . . . . . . . . . . . . . . . . . . . . 73
19.2 DebuggingUsingBreakPoints . . . . . . . . . . . . . . . . . . . . 75
19.3 Refactorings: Extract-Method, Extract-Variable . . . . . . . . . . . . 75
20 WebClient 75
20.1 GettingWebContentFromGET Requests . . . . . . . . . . . . . . . 75
20.2 PassingParameterstoPOST Requests . . . . . . . . . . . . . . . . . 76
20.3 RealtimeStockQuotes . . . . . . . . . . . . . . . . . . . . . . . . 76
21 DatabaseUsingJDBC 78
21.1 TestingJDBC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
21.2 VerifyingDatabaseContents . . . . . . . . . . . . . . . . . . . . . 80
22 JavaUI 81
22.1 TipCalculatorwithUI . . . . . . . . . . . . . . . . . . . . . . . . . 81
JavaThroughExamples 1
1 Introduction
1.1 Instructor
• AsimJalis
• HasworkedassoftwareengineeratMicrosoft, Hewlett-Packard, andSalesforce.
• http://linkedin.com/in/asimjalis
1.2 Introductions
• Whatisyourname? Whatdoyoudo?
• Howareyouplanningtousewhatyoulearnhere?
• Whatisyourperfectoutcome?
1.3 Hands-OnLearning
• Howwillthiscoursework?
– Hands-onclass.
– Learnbydoing.
• Whyhands-on?
– Helpsyougetmostoutofclass.
– Youinteractwithmaterialmoredeeply, learn.
– Encouragessmallmistakes, fasterlearning.
– Helpsgetissuesresolvedhere, now.
– Afterwardsyouretaintheexperience.
2 HistoryofJava
2.1 JavaVersions
JavaThroughExamples 2
Version Released Notes
JDK Alpha/Beta 1995 SunannouncedJavainSeptember23, 1995.
JDK 1.0 January23, 1996 OriginallycalledOak(namedaftertheoaktreeoutsideJamesGosling’soffice). RenamedtoJava1inJDK 1.0.2.
JDK 1.1 February19, 1997 IntroducedAWT eventmodel, innerclass, JavaBean, JDBC,andRMI.
J2SE 1.2 December8, 1998 CodenamePlayground. Rebrandedas”Java2”andrenamedJDK toJ2SE (Java2StandardEdition). AlsoreleasedJ2EE (Java2EnterpriseEdition)andJ2ME (Java2MicroEdition). IncludedJFC (JavaFoundationClasses-Swing, AccessibilityAPI,Java2D,PluggableLookandFeelandDragandDrop). IntroducedCollectionFrameworkandJIT compiler.
J2SE 1.3 May8, 2000 CodenameKestrel. IntroducedHotspotJVM.
J2SE 1.4 February6, 2002 CodenameMerlin. Introducedassert, non-blockingIO (nio), loggingAPI,imageIO,Javawebstart, regularexpressionsupport.
J2SE 5.0 September30, 2004 CodenameTiger. Officiallycalled5.0insteadof1.5. Introducedgenerics, autoboxing/unboxing, annotation, enum, varargs, for-eachloop, staticimport.
JavaSE 6 December11, 2006 CodenameMustang. RenamedJ2SE toJavaSE (JavaStandardEdition).
JavaSE 7 July28, 2011 CodenameDolphin. FirstversionafterOraclepurchasedSun(calledOracleJDK).
JavaSE 8 Expected2013
2.2 SupportedPlatforms
WhichplatformsdoesJavarunon?
Sun’ssloganforJavahasbeen Writeonce, runanywhere orWORA.JavacoderunsunchangedonmostmajorhardwareplatformsandoperatingsystemsincludingWin-dows, Mac, Linux, etc.
2.3 WhyJava
WhyisJavainteresting?
• JavaLibraryEcosystem. Javahasalargelibraryecosystem.
• Concurrency. Javasupportsconcurrencyoutofthebox.
• MemoryManagement. Javatakescareofmemorymanagement.
• RuntimeChecking. Javadatastructurescheckforout-of-boundsexceptionsatruntimetopreventunauthorizedaccesstomemory. Javacodeis”safer”thancodeinC orC++.
JavaThroughExamples 3
• Performance. Java’sperformanceiscomparabletoC andC++onmany bench-marks.
3 Installation
3.1 InstallingJava
Exercise: InstallJavaonyourmachine.
Solution:
• IfyouareonaMacJavacomespreinstalled.
• IfyouareonWindowsgotothislink http://www.oracle.com/technetwork/java/javase/downloads/index.html. IfyousearchGooglefor javajdkdownload thisisthefirstlink.
• Clickonthebuttonthatsays Java and Download.
• Acceptthelicenseagreementandthendownloadtheversionforyouroperatingsystem. x86means32-bit, and x64means64-bit. Ifyouarenotsurewhichonechoosex86(32-bit).
3.2 InstallingEclipse
Exercise: DownloadEclipse.
Solution:
• Goto http://www.eclipse.org/downloads.
• Downloadtheversioncalled EclipseIDE forJavaDevelopers foryouroperatingsystem.
• Ifyouarenotsurewhetheryoursystemis32-bitor64-bitdownloadthe32-bitversion.
JavaThroughExamples 4
Exercise: InstallEclipse.
Solution(Mac):
• OntheMacthiswilldownloadasa tar.gz file.
• Inaterminalwindowrun tar xvzf eclipse-file.tar.gz.
• Thiswillproduceafoldercalled eclipse. Movethistothe Applications folderusingthiscommand.
mv eclipse /Applications
Solution(Windows):
• OnWindowsthiswilldownloadasa zip file.
• Thisfillwilluncompresstoproduceafoldercalled Eclipse.
• Savethistothe C: driveorthedesktop.
4 Basics
4.1 HelloWorld
Exercise: Createahelloworldprogramonthecommandline.
Solution:
• Createafilecalled Hello.java withthesecontents.
public class Hello {public static void main(String[] args) {
System.out.println("Hello, world!");}
}
• Compileitbytypingthisintheconsole.
JavaThroughExamples 5
javac Hello.java
• Notethatthecompilerhascreatedafilecalled Hello.class inthecurrentfolder.
• Runitbytypingthisintheconsole.
java -cp . Hello
Notes:
• Javaseestheworldorganizedintoclasses. Forexample Hello isaclass.
• Thecodelivesinfunctionswiththeclasses. Here main isafunction.
• javac compilestheprogramandgeneratesthe Hello.class file.
• java runsthe Hello.class file.
• -cp standsfor classpath. Thistells java wheretolookfortheclassfile.
• When java starts it looks for the main function in theclassnamethat itwasinvokedwith. Thenitruns main.
4.2 HelloWorldEclipse
Exercise: CreateahelloworldprograminEclipse.
Solution:
• StartEclipse.
• In Selectaworkspace choosethedefaultworkspace. Click OK.
• Clickthe Workbench icon, anarrowcurvingbackwards. Whenyouhoveronthisiconitwillsay Workbench.
• Clickon File --> New --> JavaProject. For Projectname use demo. Click Finish.
• Clickon File --> New --> Package. For Name use core. Click Finish.
• Clickon File --> New --> Class. For Name use Hello. Click Finish.
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• The Hello.java filelookslikethis.
package core;
public class Hello {
}
• Changeittothis.
package core;
public class Hello {public static void main(String[] args) {
System.out.println("Hello, world!");}
}
• Clickon Run --> Run. In RunAs select JavaApplication. Click OK.
• Theapplicationwillrun. Youwillsee Hello, world! printedoutintheconsolebelow.
Notes:
• Under thehoodEclipse isdoing thesamethings thatweweredoingon thecommandline. However, itautomatesandstreamlinestherepetitiveparts.
• Eclipsehasautocomplete. Type Syst andthentype Control-Space toseetheautocompleteoptions.
• Eclipsemakesiteasytorenamepackages, classes, functions.
4.3 EclipseViews
ThepanesinEclipsearecalled views. Youcandragthemanddockthemondifferentcorners.
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Eclipsealsohasseveralperspectives. Inparticularthe Java and JavaBrowsing onesareusefulforeditingcode.
Exercise: Explorethedifferentperspectives.
Exercise: RestoreEclipseviewstotheiroriginalsettings.
Solution:
Select Window --> ResetPerspective.
4.4 Projects, Packages, Classes
Whyaretheresomanylevels?
• Javaismeantforlargeprojects.
• Projects, packages, andclassesgiveyouagoodlayeredhierarchytoorganizeprojectsspreadoutovermanyteams.
• Projectscontaintheentireapplication. Thinkoftheprojectasasinglefilethatwillbedeployedtoacustomersite.
• Packagesaregroupsofclassesthatarelogicallyrelated. Forexample, allthedatabaseclassesmightbeinasinglepackage.
• Thinkofpackagesasareacodes, andclassesasindividualphonenumbers.
• Classesarecollectionsoffunctionsanddata. ThesearethebuildingblocksofJavaprograms.
4.5 ProgramStructure
Exercise: Createaprogramthatgreetstheuserbyname.
Solution:
• CreateaprojectinEclipsecalled demo.
• Createapackagecalled core.
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• Createaclasscalled Util inthepackage.
• Putthecontentsat https://gist.github.com/asimjalis/5475179 intothisfile.
• Createaclassinthefoldercalled Demo.
• Addthefollowingtoit.
package core;
public class Demo {public static void main(String[] args) {
String name =Util.prompt("Enter your name: ");
Util.print("Hello " + name);}
}
• RuntheprogramthroughEclipse.
Notes:
• Javaclassesareplacedinpackages. Theseclassesareinapackagecalled core.
• Javastartsbyrunning main intheclassthatitisinvokedwith. Afterthistheprogramstatementsareexecutedsequentially.
• WhitespaceandindentationincodeisnotimportantandignoredbyJava. Itmakesthecodereadableforprogrammers.
• Allstatementsendwithasemicolon.
• Javastatementsconsistofassignments, functioncalls, andafewprogrammingconstructsthatwewilldiscuss.
• Functioncallsormethodcallshaveoneoftheseforms:
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// Class method.Class.method(arg1, arg2, arg3, ...)
// Instance method.instance.method(arg1, arg2, arg3, ...)
Exercise: Is Util.prompt aclassmethodoraninstancemethod?
Solution: Thisisaclassmethod. Classesconventionallystartwithupper-caseletters.Instancesstartwithlower-caseletters.
4.6 Comments
Exercise: Addcommentstothisprogram.
Solution:
package core;
/*** Greets user with name.*/
public class Demo {/*** Main.*/
public static void main(String[] args) {// Get user's name and greet him/her.String name =
Util.prompt("Enter your name: ");Util.print("Hello " + name);
}}
Notes:
• Singlelinecommentsareinsertedlikethis. Theseareusefulforcommentingcode.
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// This is a comment.
Thesecommentsstartat // andendattheendoftheline.
• Multilinecommentsareinsertedlikethis. Theseareusefulforlongerdescrip-tionsofalgorithms.
/** This is a multiline comment.*/
Thesecommentsstartat /* andendat */.
• Javadoccommentsareinsertedlikethisjustbeforeaclass, functionorvariable,describingitsintent.
/*** Describes a function.*/
Thesecommentsstartat /* andendat */.
5 Eclipse
5.1 Renaming
Whatis refactoring?
• Refactoringischangingthedesignofaprogramwithoutchangingitsbehavior.
• Thesimplestrefactoringisrenaming.
Exercise: Renamethepackagefrom core to core.examples. Makesurethepro-gramruns. Thenrevertthechange.
Solution:
• Right-clickonthepackage, andselect Refactor --> Rename.
JavaThroughExamples 11
• Typeinthenewpackagenameandthenchooseallthedefaultsettings.
Notes:
• Youcanusethesamefeaturetorenameprojects, classes, methods. Goahead.Tryit.
• Eclipsedoesalotofworkforyouduringtherenamewhichwouldbedifficulttodobyhand. Inarename, youhavetorenameandmovedirectoriesandfiles,andalsomodifythecodethatreferstotheoldnames.
• Eclipsedoesallthis. Andbecauseitisautomateditissaferthaniftherefactoringwasdonebyhand.
5.2 Exporting
Exercise: Exporttheprojectandrunitfromthecommandline.
Solution:
• Right-clicktheproject.
• Select Export. Searchfor jar. Choose RunnableJAR file. Click Next.
• For Launchconfiguration specifytheclassyouwanttorun.
• For Exportdestination specifythefullpathtoajarfilesuchas demo.jar.
• Choosethedefaultsfortheotheroptions.
• Runtheprogrambytypingontheconsole,
java -jar demo.jar
JavaThroughExamples 12
6 PrimitiveDataTypes
6.1 IntegersandFloating-PointNumbers
ThemostbasicdatatypeinJavaisthenumber. Javahasbothintegersaswellasfloatingpointnumbers. Youcanenternumbersliterallyintotheshelltoseetheirvalues.
Exercise: Guessthevaluesandtypesofthesenumberliterals: 123, 0x10, 010, 0, 1.1,1.1e3, 0.0
Solution:
Literal Value Type
123 123 int
0x10 16 int
010 8 int
0 0 int
1.1 1.1 double
1.1e3 1100.0 double
0.0 0.0 double
6.2 Variables, Types, Assignment
Exercise: Writeaprogramthatdividesarestaurantcheckof$43between3friends.
Solution:
public static void main(String[] args) {splitCheck();
}
public static void splitCheck() {int persons = 3;double amount = 43.0;
JavaThroughExamples 13
double split = amount / persons;System.out.println(
"Amount per person: "+ split);
}
Notes:
• Javastoresdatainvariables.
• Allvariablesmustbedeclaredwiththeirtypesthefirsttimetheyareused.
• The = istheassignmentoperator. Ittakesavariableonitsleftandanexpressiononitsright. Theexpressioncanbeanyarithmeticexpressionofvariablesorfunctions.
• The = operatorwritesthevalueoftheexpressionontherightintothevariableontheleft.
• Subtlepoint: = indicatesassignment, not equality. Itisanaction.
6.3 NamingConventions
Whatarevariablenamingconventions?
• Examplesofvariablenames: price, pizzaToppingCount, startDate.
• Variablesnamescancontainletters, numbers, andunderscores. Thefirstchar-acterofthenamemustbealetteroranunderscore.
• TheJavaconventionistouse camel-case names. Soavariablelike startDateshouldnotbewrittenin snake-case as start_date.
• Variablenamesand functionnamesstartwith lower-case letters, whileclassnamesstartwithupper-caseletters.
Hereisasummaryofthenamingconventions.
JavaThroughExamples 14
Entity Convention Example
Constant snake_case EARTH_RADIUS_MILES
Variable camelCase secondsBeforeLaunch
Function camelCase launchSpaceShuttle
Class PascalCase ShuttleCamera
Package snake_case shuttle.camera.filter_algorithms
Project snake_case space_shuttle_avionics
6.4 PrintfandFormat
Exercise: Writeaprogramthatdividesarestaurantcheckof$43between3friends.Printtheoutputwith2decimalplaces, andadollarsign.
Solution:
public static void splitCheck2() {int persons = 3;double amount = 43.0;double split = amount / persons;System.out.printf(
"Amount per person: $%.2f",split);
}
Notes:
• Solution2printstheoutputmorecleanly. Itputsadollarsignontheresultandtrimsittotwodecimalplaces.
• Thefirstargumentfor printf istheformatstring. Thisisatemplatewhichhasplaceholdersforthevariablesthatarepassedinasadditionalarguments.
Whatarethe printf formatcodes?
JavaThroughExamples 15
FormatCode Meaning
%d int asdecimal
%x int ashexadecimal
%f double
%s String
%b boolean
%n newlinecharacter
%c char
%% % characteritself
%.2f double with2digitsafterdecimalpoint
6.5 NumericOperators
WhatarithmeticoperatorsdoesJavahave?
Expression Result
a + b Adding a and b
a - b Subtracting b from a
a * b Multiplying a and b
a / b Dividing a by b
a % b Remainderofdividing a by b
Notes:
• Theseoperatorsdonotchangethevalueof a and b.
• Theyproduceanewvaluewhichcanbeassignedtoavariable.
JavaThroughExamples 16
• In x = a + b thevalueof a and b arenotchanged. Onlythevalueof x. Onlythevariabletotheleftof = changes.
• Theonlywaytochangethevalueofavariableisthroughanassignment.
6.6 AssignmentOperators
Exercise: A large14”pizzaat ExtremePizza costs$14.45. Each topping is$1.70.Supposewewantjalapenos, olives, artichokehearts, andsun-driedtomatoes. Howmuchwillthetotalbe?
Solution1:
public static void pizzaPrice() {
double crust = 14.45;double topping = 1.70;
// Crust.double price = crust;
// Plus 4 toppings.price = price + topping;price = price + topping;price = price + topping;price = price + topping;
System.out.printf("Pizza Price: $%.2f\n",price);
}
Notes:
• A variablecanbeassignedtomultipletimes.
• A variablecanrecycleitsownpreviousvalueontheleftof =.
JavaThroughExamples 17
• = isnotmathematicalequality. So price = price + topping isnotaparadox.
• = issimplyassignment.
Solution2:
public static void pizzaPrice2() {
double crust = 14.45;double topping = 1.70;
// Crust.double price = crust;
// Plus 4 toppings.price += topping;price += topping;price += topping;price += topping;
System.out.printf("Pizza Price: $%.2f\n",price);
}
Notes:
• Becausethepattern x = x + a occursalotthereisashort-handforit: x +=a.
• Readthisas: modify x byadding a toit.
• += iscalledanassignmentoperator.
• Itisarelativeof =.
• Ittoochangesthevalueofthevariableonlyonitslefthandside.
Whatarethedifferentassignmentoperators?
JavaThroughExamples 18
Assignment Meaning
a = b Modify a bysettingitto b
a += b Modify a byadding b toit
a -= b Modify a bysubtracting b fromit
a *= b Modify a bymultiplying b withit
a /= b Modify a bydividingitby b
a %= b Modify a bysettingittotheremainderofdividingitby b
6.7 Increment/DecrementOperators
Exercise: Add$1tothepizzapriceasadollartipforthestaff.
Solution1:
price = price + 1;
Solution2:
price += 1;
Solution3:
price++;
Notes:
• Solution1andSolution2followfromourearliernotes.
• Solution3isanotherwaytoincrementby1. Thisoccursalotinprograms. Anytimeyouwanttocountsomethingyoucountby1. Sothereisaspecialnotationforitcalledthe increment operator.
Whatarethedifferent increment and decrement operators?
JavaThroughExamples 19
Expression Meaning
++a Increment a andreturnitsnewvalue
a++ Increment a andreturnitsoldvalue
--a Decrement a andreturnitsnewvalue
a-- Decrement a andreturnitsoldvalue
Exercise: Whatwillbetheoutputofthiscode?
int i = 0;System.out.printf("%d %d %d\n", i++, i++, i++);
Exercise: Whatwillbetheoutputofthiscode?
int i = 0;System.out.printf("%d %d %d\n", ++i, ++i, ++i);
6.8 BitOperators
Withinthecomputernumbersarestoredinbytes. Eachbyteis8bits.
Howmanybytesareusedbythedifferentnumerictypes?
Type Bytes Min Max
char 2 0 65,535
boolean 1 0 1
byte 1 -128 127
short 2 -32,768 32,767
int 4 -2,147,483,648 2,147,483,647
long 8 -9,223,372,036,854,775,808 +9,223,372,036,854,775,807
float 4 1.4e-45 3.4e+38
double 8 4.9e-324 1.8e+308
JavaThroughExamples 20
Whatarethedifferentbitoperators?
Expression Meaning
a << 1 Shiftbitsof a leftby1
a >> 1 Shiftbitsof a rightby1
a >>> 1 Shiftbitsof a rightby1with0inleft-mostbit
a & b AND thebitsof a and b
a ˆ b XOR thebitsof a and b
a | b OR thebitsof a and b
~a NOT thebitsof a and b
Exercise: Colors are frequently stored as RGB values in browsers. For example0x112233 meansthecolor’s red valueis 0x11, green valueis 0x22, and blue valueis 0x33. Separateoutthered, green, andbluecomponentsofthiscolor.
Solution:
public static void colors() {
int rgb = 0x112233;int red = (rgb & 0xff0000) >> 16;int green = (rgb & 0x00ff00) >> 8;int blue = (rgb & 0x0000ff);System.out.printf("%x = %x %x %x",
rgb, red, green, blue);}
7 Strings
7.1 StringLiterals
Besidesintegersandfloating-pointnumbersyoucanalsousestringsasadatatype.Stringrepresenttext.
JavaThroughExamples 21
Exercise: Createaprogramthatcombinesfirstandlastnamestocreatefullnames.
Solution:
String firstName = "Dmitri";String lastName = "Jones";String fullName = firstName + " " + lastName;
Notes:
• Stringsmarkedbydouble-quotes.
• Stringliteralscannotbespreadacrossmultiplelines.
• Stringscanbejoinedtogetherusing +.
• + producesanewstringanddoesnotchangethevalueofthestringspassedtoit.
7.2 StringAssignmentOperator
Exercise: Therewere3unauthorizedloginsintoasystem, at3:13AM,5:17AM,and6:59AM.Allofthemoccurredon1/13/12. Createasingleerrormessagewiththe3incidents.
Solution:
public static void loginErrors() {
String errors = "";errors += "[1/13/12 3:13 AM] Unauthorized login.\n";errors += "[1/13/12 5:17 AM] Unauthorized login.\n";errors += "[1/13/12 6:59 AM] Unauthorized login.\n";System.out.print(errors);
}
Notes:
JavaThroughExamples 22
• += canbeusedtoaddtothevalueofanexistingstringvariable.
• "\n" producesanewlinecharacterinthestring.
• OnMac/Unixanewlineis "\n".
• OnWindowsanewlineis "\r\n".
• Togetnewlinesinaportablewayuse System.getProperty("line.separator").
Exercise: Createaprogramthatprintshelloandworldontwoseparatelinesandusesaportablenewlinesequence.
7.3 EscapeSequences
Whataresomeotherescapesequences?
Sequence Value
\t Tab
\n Newline
\r Carriagereturn
\' Single-quote
\" Double-quote
\\ Backslash
7.4 ConvertingBetweenStringsandNumbers
Exercise: Convertthestring "1234" intoanumber.
Solution:
String string = "1234";int intvalue = Integer.parseInt(string);System.out.printf("intValue=%d\n", intValue);
JavaThroughExamples 23
Whatarethedifferentfunctionsforconvertingnumberstostrings?
Expression Value Meaning
Integer.parseInt("1234") 1234 Integervalueofstring "1234"
Integer.parseInt("101",2) 5 Integervalueofbinarystring "101"
Double.parseDouble("1234") 1234.0 Doublevalueofstring "1234"
Integer.toString(9) "9" Decimalstringvalueofinteger 9
Integer.toString(9,2) "1001" Binarystringvalueofinteger 9
Double.toString(1234) "1234.0" Stringvalueofdouble 1234.0
Notes:
• Youcanalsoconvertnumberstostringbyconcatenatingthemwithastring, likethis "" + 1234.
• However, unlessthisisnaturallyapartofalongerstringusingthe toStringfunctionsispreferred.
7.5 TipCalculator
Exercise: Writeatipcalculator. Asktheuserfortotalcheckamount, numberofpeople,andtiprate. Printoutthetotaltip, andtheamountperperson.
Solution:
public static void tipCalculator() {
double amount = Double.parseDouble(Util.prompt("Amount: "));
int people = Integer.parseInt(Util.prompt("People: "));
double tipRate = Double.parseDouble(Util.prompt("Tip Rate: "));
double tip = amount * tipRate / 100.0;
JavaThroughExamples 24
double newAmount = amount + tip;double share = newAmount / people;System.out.printf(
"Amount: $%.2f\n" +"People: %d\n" +"Tip Rate: %.2f%%\n" +"Tip: $%.2f\n" +"Share: $%.2f\n",amount,people,tipRate,tip,share);
}
7.6 PopulationCalculator
Exercise: ThepopulationofCaliforniain2012was38,000,000andthegrowthratewas1%. Thepopulationcanbeestimatedas,
pop = popInitial *Math.pow(1 + growthRate, years);
Here years isthenumberofyearssince2012, popInitial isthepopulationin2012.Asktheuserfortheyeartheywanttoprojectoutuntilandpredictthepopulationforthespecifiedyear.
7.7 HousePrices
Exercise: Writeaprogramthatasksuserforcurrentpriceofhouse, appreciationrate,andnumberofyearstoprojectoutintothefuture. Theprogramprintsthepriceafterthespecifiednumberofyears. Iftheinitialpriceofahouseis priceInitial thenitsfinalpriceafteryearswillbe:
price = priceInitial *Math.pow(1 + rate, years);
Here rate istheappreciationrate.
JavaThroughExamples 25
8 Branching
8.1 If, If-Else
Sofarourprogramhashadalinearlogic. Itstartsatthebeginning, runs, andterminates.Thereisnointelligenceordecisionmakingabilityinit.
Exercise: Writeacoin-flippingappthatprintsheadsortails.
Solution1:
public static void coin() {int flip = Util.randomInt(0,1);System.out.println(
"Coin: " + flip);}
Solution2:
public static void coin() {int flip = Util.randomInt(0,1);String flipOutcome;if (flip == 0) {
flipOutcome = "tails";}else {
flipOutcome = "heads";}System.out.println(
"Coin: " + flipOutcome);}
Notes:
• Solution2producesmoreuserfriendlyoutput.
Exercise: Writeaprogramthatcalculatesalettergradebasedonastudent’sGPA.
JavaThroughExamples 26
Grade GPA Minimum
A 3.5
B 2.5
C 1.5
D 1.0
F 0.0
Solution:
public static void gpa() {double gpa =
Double.parseDouble(Util.prompt("GPA: "));
String grade;if (gpa >= 3.5) {
grade = "A";}else if (gpa >= 2.5) {
grade = "B";}else if (gpa >= 1.5) {
grade = "C";}else if (gpa >= 1.0) {
grade = "D";}else {
grade = "F";}System.out.printf(
"Grade: %s\n",grade);
}
JavaThroughExamples 27
Notes:
• The if/else constructrepresentsaforkintheroad.
• Theprogramevaluateseachconditionandtakesthefirstbranchwhosecondi-tionistrue.
• Ifnoconditionistruethenittakesthe else clause.
• The else if andthe else areoptional.
• Soifnoconditionistrue, andthereisno else clausethenitignoresthewholeconstruct.
• gpa >= 3.5 isabooleanexpression. Itiseithertrueorfalse.
• >= isarelationaloperator.
8.2 RelationalOperators
Whatarethedifferentrelationaloperators?
RelationalOperators IsTrueWhen
a < b a islessthan b
a <= b a islessthanorequalto b
a > b a isgreatthan b
a >= b a isgreatthanorequalto b
a == b a isequalto b
a != b a isnotequalto b
Notes:
• Rememberthat = isassignmentandnotequality. Equalityis ==.
• Everyonetripsonthisseveraltimes.
JavaThroughExamples 28
• Notethattheseoperatorsonlyworkonnumbersandnumber-likethings(char-actersandbytes). Theydon’tworkonstringsorotherJavatypes.
8.3 Booleans
Exercise: Amazonoffersfreeshippingifyouspend$25ormore. Computeabooleanvariablecalled isShippingFree, given sales.
Solution:
public void shippingFree() {double sales = 26.00;boolean isShippingFree =
sales >= 25;System.out.printf(
"isShippingFree=%b\n",isShippingFree);
}
8.4 BooleanOperators
Booleanexpressionshavevalues true or false. Theycanbecombinedwithlogicaland, or, and not operations.
Exercise: Createagameinwhichyouflipacointwice. Ifyougettwodifferentthings(headsandtails, ortailsandheads)youwin, otherwiseyoulose.
Solution:
public static void twoCoins() {int flip1 = Util.randomInt(0,1);int flip2 = Util.randomInt(0,1);boolean won =
(flip1 == 0 && flip2 == 1) ||(flip1 == 1 && flip2 == 0);
System.out.printf("flip1=%d\n" +"flip2=%d\n" +
JavaThroughExamples 29
"won=%b\n",flip1, flip2, won);
}
Whatarethedifferentbooleanoperators?
Expression IsTrueWhen
a && b a is true and b is true
a || b a is true or b is true
!a a is false
Notes:
• The &&, || and ! operatorsonlycomputebooleanexpressions. Theydon’tchangethevalueofexistingvariables.
8.5 StringComparisonandEquality
Exercise: ConverttheairportcodeforBayAreaairportsintotheairportname.
Solution:
public static void airports() {String code = "SFO";String airport;if (code.equals("SFO")) {
airport = "San Francisco";}else if (code.equals("OAK")) {
airport = "Oakland";}else if (code.equals("SJC")) {
airport = "San Jose";}
JavaThroughExamples 30
else {airport = "Unknown";
}
System.out.printf("airport=%s\n", airport);
}
Notes:
• == onlyworksforprimitiveandnumerictypes.
• Withnon-primitivenon-numerictypessuchas String (andallotherobjects),checkforequalityusingthe .equals functionratherthanusing ==.
Exercise: Turnthisintoaprogramthatgetstheairportcodefromtheuser.
8.6 TernaryOperator
Exercise: Writeacoinflippingappthatprintsoutheadsortails.
Solution1:
public static void coin() {int flip = Util.randomInt(0,1);String flipOutcome;if (flip == 0) {
flipOutcome = "tails";}else {
flipOutcome = "heads";}System.out.println(
"Coin: " + flipOutcome);}
Solution2:
JavaThroughExamples 31
public static void coin() {int flip = Util.randomInt(0,1);String flipOutcome =
flip == 0 ? "tails" : "heads";System.out.println(
"Coin: " + flipOutcome);}
Notes:
• Theternaryoperatorletsyouwriteconditionalcodemoreconciselyforsimplerexpressions.
• Theternaryoperatorislikethe IF inExcel.
• a ? b : c. If a istrue, thisevaluatesto b. Otherwiseitevaluatesto c.
Exercise: ConverttheairportcodeforBayAreaairportsintotheairportname. Gettheairportcodefromtheuser.
Solution:
public static void airports2() {String code = Util.prompt(
"Airport code: ");String airport =
code.equals("SFO") ? "San Francisco" :code.equals("OAK") ? "Oakland" :code.equals("SJC") ? "San Jose" :"Unknown";
System.out.printf("airport=%s\n", airport);
}
Notes:
• Youcandothisusinganif-thenstatement. However, frequentlyifyouhavealistofcasesyoucandealwiththemwithatablebuiltusingternaryoperators.
JavaThroughExamples 32
8.7 Switch
Exercise: Convertnumericdaysoftheweektowords.
Solution:
public static void daysToWords() {
String input = Util.prompt("Day (1-7): ");
int dayInt = Integer.parseInt(input);String day;switch (dayInt) {
case 1:day = "Sun";break;
case 2:day = "Mon";break;
case 3:day = "Tue";break;
case 4:day = "Wed";break;
case 5:day = "Thu";break;
case 6:day = "Fri";break;
case 7:day = "Sat";break;
default:day = "Unknown";break;
}
JavaThroughExamples 33
System.out.printf("day=%s\n", day);
}
Notes:
• The switch statementisanotherwaytobranch.
• BeforeJava7 switch couldonlyhandlecasesthatwereintegers(orinteger-likesuchas enum whichwewillseelater). InJava7andlateryoucanusestringsaswell.
• The break isimportant. Ifitisleftouttheprogramwillexecutethefollowingcasesaswell.
8.8 OperatorPrecedence
Whatistheorderorprecedenceinwhichoperatorsareapplied?
Hereistheprecedenceindecreasingorder.
Operators Precedence
postfix i++ i--
unary ++i --i +i -i ~ !
multiplicative * / %
additive + -
shift << >> >>>
relational < > <= >= instanceof
equality == !=
bitwiseAND &
bitwiseexclusiveOR ˆ
bitwiseinclusiveOR |
logicalAND &&
JavaThroughExamples 34
logicalOR ||
ternary ? :
assignment = += -= *= /= %= &= ˆ= |= <<= >>= >>>=
Notes:
• Whileyoucanrelyontheprecedenceitissafertouseexplicitparenthesestocontrolprecedence.
• Thiswaythecodeisalsoeasiertounderstandforsomeoneelse.
9 Looping
9.1 LoopingwithWhile
Exercise: Pickanumberfrom1to10andthenprompttheusertoguessit.
Solution:
public static void guessNumber() {int number = Util.randomInt(1,10);int guess = -1;Util.print("I picked a number.");while (number != guess) {
String guessString = Util.prompt("Guess what number I picked: ");
guess =Integer.parseInt(guessString);
if (number == guess) {Util.print(
"Yes, you guessed right.");}else {
Util.print("You were wrong. " +
JavaThroughExamples 35
"Try again.");}
}
Notes:
• Theprogramkeepsrunningthecodein the while blockuntil theconditionbecomesfalse.
• Youcanuse break tobreakoutofaloop.
• Youcanuse continue toskiptherestoftheblockandrestarttheloop.
Exercise: Theprogramshouldgivetheuserahintandmentionifthenumberishigherorlower.
Exercise: Eliminatetheinelegantdeclarationof guess outsidetheloopandthemag-icalvalueof -1. Dothisbyusing while (true) andthen break whentheuserguessescorrectly. Thiseliminatestheneedfortheearlydeclarationof guess.
9.2 Break, Continue
Exercise: Repeatedlyplaytheguessinggamefromthepreviousexerciseswiththeuser.Exittheprogramwhentheuserpresses "q".
Solution:
public static void guess() {OUTER_LOOP:while (true) {
// Pick number.int number = Util.randomInt(1, 10);System.out.println("Picked number");
// Loop until user guesses.while (true) {
// Get user's guess.
JavaThroughExamples 36
String guessString = Util.prompt("Guess: ");
// Exit if user types "q".if (guessString.equals("q")) {
System.out.println("Exiting");break OUTER_LOOP;
}
// Restart if user types "r".if (guessString.equals("r") {
System.out.println("Restarting");continue OUTER_LOOP;
}
// Check guess.int guess = Integer.parseInt(guessString);if (guess == number) {
System.out.println("You're right!");break;
} else if (guess < number) {System.out.println("Guess too low");
} else {System.out.println("Guess too high");
}}
}}
Notes:
• Labelsareusefulwhenyouhavenestedloopsandyouwant tobreakoutofmultipleloopsatthesametime, orrestartanouterloopfromaninnerloop.
• Labeltheloopyouwanttobreakoutofwithalabelsuchas OUTER_LOOP:.
• Then break OUTER_LOOP willbreakoutoftheloopwiththegivenlabel.
• Also continue OUTER_LOOP willrestarttheouterloop.
JavaThroughExamples 37
9.3 LoopingwithFor
Exercise: Printthemultiplicationtablefor 7.
Solution1:
public static void table1() {int number = 7;
int times = 1;while (times <= 10) {
int product = number * times;System.out.printf("%d * %d = %d %n",
number, times, product);times++;
}}
Solution2:
public static void table2() {int number = 7;
for (times = 1 ; times <= 10 ; ++times) {int product = number * times;System.out.printf("%d * %d = %d %n",
number, times, product);}
}
Notes:
• The for loopisequivalenttothe while loop. Exceptitgroupstheinitializa-tion, condition, andincrementstepsatthebeginning. Thiswayitiseasiertorememberallofthem.
• Youcanbreakoutofa for loopwith break.
JavaThroughExamples 38
• Youcanrestarta for loopatthenextincrementalvaluewith continue.
• Ifyouareusing the for loop forcounting theconvention is touse i as theindex.
Exercise: Flipacoin100times, reportthetotalnumberofheadsandtails, andreportwhichsidewon.
Solution:
public static void manyFlips() {int flipCount = 100;int heads = 0;int tails = 0;for (int i = 0 ; i < flipCount ; ++i) {
int flip = Util.randomInt(0,1);if (flip == 0){ tails++; }else{ heads++; }
}
String winner =heads > tails ? "Heads" :tails > heads ? "Tails" :
"Draw";
System.out.printf("Heads: %d\n" +"Tails: %d\n" +"Winner: %s\n",heads, tails, winner);
}
Notes:
• If youareusing the for loop todo something N numberof times, then theconventionistotake i from0until N - 1.
JavaThroughExamples 39
9.4 NestedLoops
Exercise: Writethemultiplicationtablesforallnumbersfrom1through10.
Solution:
public static void tables() {for (int i = 1 ; i <= 10 ; ++i) {
for (int j = 1 ; j <= 10 ; ++j) {System.out.printf(
"%d * %d = %d\n",i, j, i * j);
}}
}
9.5 LoopingwithDo-While
Exercise: Pickanumberfrom1to10andthenprompttheusertoguessit. Stopiftheuserguesses0oranegativenumber.
Solution:
public static void guessNumber2() {int number = Util.randomInt(1,10);Util.print("I picked a number.");int guess = -1;do {
String guessString = Util.prompt("Guess what number I picked: ");
guess = Integer.parseInt(guessString);if (number == guess) {
Util.print("Yes, you guessed right.");
}else if (number < 0) {
Util.print("Quitting.");}
JavaThroughExamples 40
else {Util.print(
"You were wrong. " +"Try again.");
}}while (guess > 0);
}
Notes:
• Do-whilepushesthecheckattheendoftheloopinsteadofthebeginning.
• Dependingontheproblemyouaresolving, sometimesthisleadstoacleanersolution.
10 StringsandCharacters
10.1 CharacterLiterals
Exercise: Assume a is1, b is2, andsoon. Addupallthelettersinawordandfindoutitsnumericalvalue.
Solution:
public static void numberValue() {while (true) {
// Get user input.String input =
Util.prompt("Text: ");
// Lower-case it.input = input.toLowerCase();
// Check for quit.if (input.equals("q"))
JavaThroughExamples 41
break;
// Calculate value of text.int value = 0;for (int i = 0
; i < input.length(); ++i) {// Get char at position i.char c = input.charAt(i);
// Is it a letter?if ('a' <= c && c <= 'z')
value += c - 'a' + 1;}
// Print the final value.System.out.println(
"Value: " + value);}
}
Notes:
• Stringsaremadeupofcharacters. Youcangetthecharacterataspecificpositioninastringusingthe charAt function.
• Charactersbehavelikeintegers. Youcancomparethemagainstothercharac-ters.
• Youcansubtractcharactersfromeachothertogettheirrelativedistance.
• Charactersarewrittenwithsinglequotes. Forexample, 'a'.
10.2 AccessingStringCharacters
Exercise: Writeaprogramthattakesabinarystringof0’sand1’sandthenprintsitsdecimalvalue.
Solution:
JavaThroughExamples 42
public static void binaryValue() {while (true) {
// Get user input.String input = Util.prompt(
"Enter binary number: ");
// Check for quit.if (input.equals("q")) {
break;}
// Calculate valueint value = 0;int multiplier = 1;for (int i = input.length() - 1 ; i >= 0 ; --i) {
char c = input.charAt(i);int x = c == '0' ? 0 : 1;value += multiplier * x;multiplier *= 2;
}Util.print("Value: " + value);
}}
Notes:
• Characterscanbecomparedforequalityusing ==.
• Youcanscanastringfrombeginningtoendorbackwards, whicheverworksmoreelegantlyforyouralgorithm.
11 ConstantsandStaticMethods
11.1 Constants
Exercise: Addaconstant PI toaclasscalled Constants.Solution:
JavaThroughExamples 43
public class Constants {public static final double PI = 3.141529;
public static void main(String[] args) {System.out.println(
"PI = " + Constants.PI);}
}
11.2 StaticFields
Exercise: Addastaticfieldwhichspecifieswhether theprogramisrunningin trialmodeorofficiallyregistered.
Solution:
public class License {public static boolean isRegistered = false;
public static void main(String[] args) {System.out.println(
"isRegistered= " +License.isRegistered);
}}
11.3 StaticMethods
Exercise: Writeafunctionthatasksauserhisorhernameandthenreturnsagreeting.
Solution:
public static String getGreeting(String name) {String greeting = "Hello, " + name;return greeting;
}
JavaThroughExamples 44
public static void testGetGreeting() {String greeting =
getGreeting("Dmitri");System.out.printf(greeting);
}
Notes:
• The public keywordsaysthatthefunctioncanbeaccessedfromanywhere.
• The static keywordsaysthatthisfunctionshouldbeinvokedas Class.function,where Class isthenameoftheclassthatthisfunctionisin.
• Functionsandmethodsareinterchangeablenamesforthesameconcept. Non-staticfunctionsareusuallycalledmethods.
• String beforethefunctionnameindicatesthereturntype.
• Ifafunctionhasareturntypeof void itdoesnotreturnanything. Itisaproce-durethatdoessomeworkandends.
• String name istheargumentthatispassedtothefunction.
• Withinthefunctionthe return greeting isrequiredbecausethefunctiondeclarationpromisedthatitwasgoingtoreturna String object.
• Theargumentsthatarepassedtothefunctionwhenitisinvokedareaccessiblewithinthefunctionthroughtheparameternames.
11.4 Overloading
Exercise: Writeafunctionthattakesafirstnameandalastnameandreturnsagreeting.
Solution:
public static String getGreeting(String firstName,String lastName) {
String greeting = "Hello, " +
JavaThroughExamples 45
firstName + " " + lastName;return greeting;
}
public static void testGetGreeting() {String greeting =
getGreeting("Dmitri", "Jones");System.out.printf(greeting);
}
Notes:
• Multiplefunctionscancoexistiftheytakedifferenttypesofarguments. Sothesetwo getGreeting functionscanliveinthesameclass.
11.5 Visiblity, Namespaces, Import
Whatarethelevelsofvisibilitiesforfunctions?
Visibility Keyword Visible
Default Inclassandpackage
Public public Inclass, package, andotherpackages
Private private Inclass
Protected protected Inclassandsubclasses
Exercise: Canwemakethefunctionsinthepreviousexercisedefault? Canwemakethemprivate?
Notes:
• Namespacesaredeterminedbypackagenames.
• A classmayrefertootherclasseswithinitspackagedirectlybytheirnames.
JavaThroughExamples 46
• A classmayrefertootherclassesoutsideitspackageeitherbyfullyspecifyingthepackagename. Forexample com.otherpackage.Class.
• import com.otherpackage.Class lets Class bereferredtodirectly.
• import com.otherpackage.* letsallclassesinthatpackagebereferredtodirectly.
• import static com.otherpackage.Class.* letsallmembersof Classbereferredtodirectly.
• import static com.otherpackage.Class.field lets field insideClass bereferredtodirectly.
Whatarethedifferentkindsofimports?
ImportSyntax Meaning
import core.util.Math Useclass Math inpackage core.util as Math
import core.util.* Useallclassesinpackage core.util directly
import static core.util.Math.PI Usemember PI in Math directly
import static core.util.Math.* Useallfunctionsandfieldsof Math directly
Exercise: Createaclasscalled Constants. Create NL as System.getProperty("line.separator").Staticallyimportitandprintit.
Exercise: Addthecontant PI to Constants.
12 FileI/O
12.1 ReadFiles
Exercise: LookatthecodeforreadingafileinUtil.java. Usethattocreatecodetoreadafileline-by-line.
JavaThroughExamples 47
12.2 WritingFiles
Exercise: LookatthecodeforwritingafileinUtil.java.
12.3 AppendingtoFiles
Exercise: LookatthecodeforappendingtoafileinUtil.java.
13 ObjectsandClasses
13.1 ObjectsandClasses
Whydoweneedobjectsandclasses?
• Inproceduralprogramming, theprogramstateisglobal. Anyfunctioncanac-cessanyglobalvariable.
• Objectssplituptheglobalstateintosmallerchunks.
• Thiswayifthereareissueswithaprogramitiseasiertonarrowitdowntoonepartofthecode.
• Object-orientedprogramminghasmadepossiblethecomplexsoftwaresystemsthatwehavetoday. Theinternet, thesmartphone, thevideogamingconsoles,allrelyonobject-orientedprogrammingformanagingcomplexity.
13.2 DefiningandUsingObjects
Exercise: CreateaFileobjectthatisinitializedwithapath, andallowsausertoreadthefile, writethefile, andappendtothefile.
Solution:
CreateaFileclass.
JavaThroughExamples 48
public class File {private String path;
public File(String path) {this.path = path;
}
public String read() {return Util.fileRead(path);
}
public void write(String contents) {Util.fileWrite(path, contents);
}
public void append(String contents) {Util.fileAppend(path, contents);
}}
Nowtestit.
public static void fileTest() {File file = new File("/tmp/file123");file.write("Line 1\n");file.append("Line 2\n");Util.print("File:\n" + file.read());
}
Notes:
• Theinstancevariablesofanobjectarelistedinsidetheclasswiththemethods.Theyarealsoknownasfields.
• Allnon-staticmethodsinaclasshaveaccesstoitsinstancevariablesorfields.
• Theconstructorhasthesamenameastheclass. Itsetthefieldstotheirinitialvalues.
JavaThroughExamples 49
• Todisambiguatetheparameter path fromthefield path themethodscanusethis.path whichalwaysreferstothefield.
• Ifthereisnoparameterorlocalvariablewiththatname path referstothefieldaswell.
• Theobjectiscreatedusing new File(path), whichcallstheconstructor.
• A classcanhavemultipleconstructorsaslongastheyhavedifferentparameters(bycountorbytype).
13.3 ObjectsversusStaticMethods
Whygodoallthistroubleofcreatingclasses? Whynotjusthavestaticmethods?
• Theobject File hidesitsimplementation.
• Youcancompletelyguttheimplementationandtheusersoftheclasswillnotknow.
• Forexample, insteadofstoringthecontentsonthediskyoucouldstorethemonAmazonS3inthecloudoronDropbox.
• Objects create this abstractionboundarybetween the code that implementsfunctionalityandthecodethatusesit.
• Thecodethatusesanobjecttreatsitlikeablackbox.
• Theseobjects are like adriverdrivinga carwithoutunderstandinghow theengineworks.
13.4 Visibility
Whichmethodsandfieldsonanobjectcanothercodeaccess?
• Generallyothercodecanaccessmethodsandfieldsmarked public.
• Code in the samepackagewillalsobeable toaccessfields thataredefault(meaningtheyhavenovisibilityqualifiers).
• Tomakesurenooneoutsideaclasscanaccessafieldmarkit private.
JavaThroughExamples 50
13.5 Interfaces
Exercise: DefineaStorageclassofwhichFileisaspecificinstance.
Solution:
InStorage.java,
public interface Storage {String read();void write(String contents);void append(String contents);
}
InFile.java,
public File implements Storage {// Other code remains unchanged.
}
IntestingFile, replacethe File declarationwith Storage declaration.
Notes:
• Interfacesdefinetheminimalcontractaclasshastofulfillbeforeitcanbeusedbyothercodeasanimplementationoftheinterface.
• Ifyourcodereliesoninterfacesratherthanconcreteclassesyoucaneasilypassindifferentimplementationsindifferentscenarios.
• Forexample, youcanpassinacloudstorageclassinsteadofadisk-basedfilestorageclass.
• Fortestingyoucanpassinamemory-basedstorageclass.
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13.6 In-MemoryFile
Exercise: Implementamemory-basedimplementationoftheStorageinterface.
Solution:
package demo;
public class MemoryFileimplements Storage {
private String contents;
public String read() {return contents;
}
public void write(String contents) {this.contents = contents;
}
public void append(String contents) {this.contents += contents;
}}
13.7 AnonymousClasses
Exercise: Implementamemory-basedimplementationoftheStorageinterfaceusingananonymousclass.
Solution:
public static void testStorage() {Storage storage = new Storage() {
private String contents;
public String read() {return contents;
JavaThroughExamples 52
}
public void write(String contents) {this.contents = contents;
}
public void append(String contents) {this.contents += contents;
}};
storage.write("Line 1\n");storage.append("Line 2\n");Util.print("Storage:\n" + storage.read());
}
13.8 Inheritance
Exercise: Createaclasscalled AppendingFile whichappendsbothonwriteandonappend.
Solution:
package demo;
public class AppendingFile extends File {public AppendingFile(String path) {
super(path);}
public void write(String contents) {append(contents);
}}
JavaThroughExamples 53
13.9 EnumTypes
Exercise: Createaclass forcalculatingstatesales taxdependingonthecustomer’sstate.
Solution1:
public enum State {CA,WA,OR
}
public static double getSalesTax(State state, double amount) {double taxRate =
state == State.CA ? 0.075 :state == State.WA ? 0.065 :state == State.OR ? 0.000 :
0.000;return amount * taxRate;
}
public static void checkState() {System.out.println(
getSalesTax(State.CA, 30.0));}
Solution2:
public enum State {CA(0.075),WA(0.065),OR(0.000),UNKNOWN(0.000);
private final double taxRate;
JavaThroughExamples 54
private State(double taxRate) {this.taxRate = taxRate;
}
public double getSalesTax(double amount) {
return amount * taxRate;}
}
public static void checkState() {System.out.println(
State.CA.getSalesTax(30.0));}
Notes:
• Solution1usesenumtypesinthesimplestwayasasimpleenumeratedtype.
• Solution2addssomefunctionalityanddatatoeachenumvalueaswell.
13.10 NestedClasses
Javaletsyounestclassesinsideeachother. Thisisusefulforenumtypesandothertypicallysmallclasses.
Exercise: Createan App class containinganother class called Coin which returnsCoin.Head and Coin.Tails.
Solution:
public class App {public static void main(String[] args) {
Flipper flipper =new Flipper();
System.out.println(flipper.flip());
JavaThroughExamples 55
}
public static enum Coin {HEADS,TAILS;
}
public static class Flipper {Coin flip() {
int flip =Util.randomInt(0,1);
if (flip == 0)return Coin.TAILS;
elsereturn Coin.HEADS;
}}
}
14 Exceptions
14.1 CatchingExceptions
Exercise: Writeafunction promptIntwhichrepeatedlyaskstheuserforan int untiltheusersubmitsavalid int.
Solution:
public static int promptInt(String prompt) {while (true) {
try {String input =
Util.prompt(prompt);return Integer.parseInt(input);
}catch(Exception e) {
Util.print("Invalid input");
JavaThroughExamples 56
}}
}
public static void promptIntTest() {int intValue = promptInt("Integer: ");System.out.println(intValue);
}
Notes:
• Youcancatchallexceptionsbycatching Exception. Youcanalsocatchnar-rowertypesofexceptions.
• A catchlistingaparticularexceptionwillcatchthatexceptiontypeaswellasallofitssubclasses.
Exercise: Havetwocatchclauses: onefor NumberFormatException andanotheroneforallotherexceptions.
14.2 ThrowingExceptions
Exercise: Createaprogramthatthrowsanexceptionrandomlywithaprobabilityof0.5.
Solution:
public static void randomFailure() {if (Util.randomInt(0,1) == 0) {
throw new RuntimeException("Random exception.");}
}
Notes:
• Ifyouthrowa RuntimeException youdonothavetodeclareitinthemethodsignature.
• Testthisbychangingtheexceptiontypeto Exception.
JavaThroughExamples 57
14.3 Finally
Exercise: Createaprogramthatthrowsanexceptionrandomlywithaprobabilityof0.5, andprintsamessagetoshowifexceptionwasthrown.
Solution:
public static void randomFailure() {try {
if (Util.randomInt(0,1) == 0) {throw new RuntimeException("Random exception.");
}System.out.println("No Exception");
}catch (Exception e) {
System.out.println("Exception!");}finally {
System.out.println("Returning");}
}
Notes:
• Codeinthe finally blockisalwaysexecutedregardlessofwhetheranexcep-tionisthrownornot.
• Thisisusefulforcleaningupaftercodeisrun. Thecleanupmustoccurregard-lessofwhetherthecodethrowsanexceptionornot.
• Forexample, whenyouopenafilestreamoradatabasehandle, use finallytoclosethem.
JavaThroughExamples 58
15 Arrays
15.1 ArrayLiterals
Exercise: Defineanarraycontainingthewordsfirst, second, etc. Whenauserpassesinavalueconvertittoaword. Createafunctionforthis.
Solution:
public static void numberNames() {String[] numberNames = {
"one","two","three","four",
};String numberString = Util.prompt(
"Enter number (1-4): ");int number =
Integer.parseInt(numberString);int index = number - 1;String numberName = numberNames[index];System.out.printf(
"You typed %s.\n",numberName);
}
Notes:
• Youcandefinearraysandpopulatetheminyourcode.
• Arrayshavefixedlength. Youcannotaddmoreelementstothem.
15.2 LoopingthroughArrays
Exercise: WriteaprogramthatprintsouttheStarWarsmovietitles.
JavaThroughExamples 59
Year Episode MovieTitle
1977 EpisodeIV A NewHope
1980 EpisodeV TheEmpireStrikesBack
1983 EpisodeVI ReturnOfTheJedi
1999 EpisodeI ThePhantomMenace
2002 EpisodeII AttackOfTheClones
2005 EpisodeIII RevengeOfTheSith
Solution1:
public static void starWars1() {String[] movies = {
"A New Hope","The Empire Strikes Back","Return Of The Jedi","The Phantom Menace","Attack Of The Clones","Revenge Of The Sith"
};
for (int i = 0 ; i < movies.length ; ++i) {System.out.printf(
"%d. %s\n",i, movies[i]);
}}
Solution2:
public static void starWars2() {String[] movies = {
"A New Hope",
JavaThroughExamples 60
"The Empire Strikes Back","Return Of The Jedi","The Phantom Menace","Attack Of The Clones","Revenge Of The Sith"
};
for (String movie : movies) {System.out.printf(
"%s\n",movie);
}}
Notes:
• Solution2ismoreconcise. However, itdoesnothaveaccesstotheindex.
• IfyouneedtheindexyoushoulduseSolution1. OtherwiseuseSolution2.
16 Collections
16.1 Collections
Whatarecollections?
Collectionsaredatastructuresforholdingmultipleobjectsinonevariable.
16.2 Lists
Exercise: PrintthenamesofBayAreacounties:
• Alameda• ContraCosta• SanFrancisco
JavaThroughExamples 61
• SanMateo• SantaClara
Solution:
public static void counties() {// Create array list.List<String> counties =
new ArrayList<String>();
// Add counties to it.counties.add("Alameda");counties.add("Contra Costa");counties.add("San Francisco");counties.add("San Mateo");counties.add("Santa Clara");
// Print all counties.for (String county : counties) {
System.out.println(county);}
}
Notes:
• Thelistneedstohaveatype, inthiscase String.
• List istheinterface, while ArrayList istheimplementation.
• Wecoulddeclarethe counties objectasbeingoftype ArrayList<String>aswellifwewantedto.
• Whatistheadvantageofdeclaringita List<String>? Wecanswapouttheimplementationlaterwithoutchangingalotofthecode.
16.3 ListMethods
Whatareuseful List methods?
JavaThroughExamples 62
Method Result
list.add(item) Add item to list
list.get(i) Gets item atindex i
list.size() Getsnumberofitemsinlist
16.4 PrimitiveCollections
Exercise: Createalistofthenumbers1, 2, 3, andprintthem.
Solution:
public static void numberList() {// Create array list.List<Integer> numbers =
new ArrayList<Integer>();
// Add numbers to it.numbers.add(1);numbers.add(2);numbers.add(3);
// Print all numbers.for (int number : numbers) {
System.out.println(number);}
}
Notes:
• Collectiontypescanonlystoreobjects, notprimitivetypes.
• Soeveryprimitivetypehasawrapperobject. Forexample, int hasawrapperobjectcalled Integer.
JavaThroughExamples 63
• Javaautomaticallyconvertstheprimitivedatatypeintoitswrapperobjectandback. Thisiscalledboxingandunboxing, respectively.
• Youonlyneedtousethewrapperobjectinthedeclarations.
16.5 WrapperObjects
Whatarewrapperobjects?
Primitivedatatypeshavewrapperobjectsthatallowthemtointeractwithcollectionsandotherinterfacesthatrequireobjects. Hereisalistoftheprimitivetypesandtheirwrapperobjects.
PrimitiveType WrapperObject
byte Byte
short Short
int Integer
long Long
float Float
double Double
char Character
boolean Boolean
16.6 Maps
Exercise: PrinttheBayAreaairportswiththeirabbreviation.
AirportCode AirportName
SFO SanFrancisco
SJC SanJose
OAK Oakland
JavaThroughExamples 64
Solution:
public static void airports() {// Create map list.Map<String,String> airports =
new LinkedHashMap<String,String>();
// Add airports to it.airports.put("SFO", "San Francisco");airports.put("SJC", "San Jose");airports.put("OAK", "Oakland");
// Print all airports.for (String airportCode : airports.keySet()) {
System.out.printf("%s: %s\n",airportCode,airports.get(airportCode));
}}
Exercise: WriteaprogramthatmapsPLU (productlookup)codestoapplesusingthistable. Itquitswhentheusertypes”quit”.
Fruit PLU Code
RedDelicious 4016
PinkLady 4130
Macintosh 4154
Jazz 3294
Solution:
public static void apples() {// Build map of apples.
JavaThroughExamples 65
Map<String,String> pluMap =new HashMap<String,String>();
pluMap.put("4016", "Red Delicious");pluMap.put("4130", "Pink Lady");pluMap.put("4154", "Macintosh");pluMap.put("3294", "Jazz");
// User loop.while (true) {
String plu =Util.prompt("PLU: ");
if (plu.equals("quit")) {break;
}
else if (!pluMap.containsKey(plu)) {Util.print(
"Unknown PLU " +plu);
continue;}
String fruit = pluMap.get(plu);Util.print(
"Fruit: " + fruit);}
}
Notes:
• Objectsoftype HashMap canbeassignedtovariablesoftype Map. Thismakesiteasytoswitchmapimplementationslateron.
16.7 MapMethods
Whatareuseful Map methods?
JavaThroughExamples 66
Method Result
map.keySet() Keysof map foriteratingin for loop
map.containsKey(key) Trueif map contains key
map.put(key, value) Adds key and value pairto map
map.get(key) Gets value correspondingto key
map.size() Getsnumberofkey-valuepairsinmap
Notes:
• Ifakeydoesnotexistinthemap, get returns null.
• Ifakeydoesnotexistinthemap, andthevalueisaprimitivetype, andlikelytobenull, thenyoushouldgetitasawrapperobjectandthenunboxitaftercheckingfornull; otherwise, anullwrapperobjectwillproduceanullpointerexception.
16.8 MapTypes
WhatarethedifferentkindsofMapobjects?
Type KeySortingPolicy
HashMap Keepskeysinrandomorder
TreeMap Keepskeyssortedorder
LinkedHashMap Keepskeysininsertionorder
Notes:
• HashMap isthefastestandmostspace-efficient.
• Thisisusedunlessthereisarequirementrelatedtokeyorder.
JavaThroughExamples 67
16.9 Sets
Exercise: WriteaprogramthatchecksifanIP addressislocalhost.
Solution:
public static void localhost() {Set<String> localAddresses =
new HashSet<String>();localAddresses.add("127.0.0.1");localAddresses.add("localhost");localAddresses.add("::1");localAddresses.add("");while (true) {
String input =Util.prompt("IP: ");
if (localAddresses.contains(input)) {Util.print("localhost");
}else {
Util.print("NOT localhost");}
}}
Notes:
• Objectsoftype HashSet canbeassignedtovariablesoftype Set. Thismakesiteasytoswitchsetimplementationslateron.
16.10 SetMethods
Whatareuseful Set methods?
Method Result
JavaThroughExamples 68
set.contains(item) Trueif set contains item
set.add(item) Adds item to set
set.size() Getsnumberofitemsin set
16.11 SetTypes
WhatarethedifferentkindsofSetobjects?
Type ElementSortingPolicy
HashSet Keepselementsinrandomorder
TreeSet Keepselementssortedorder
LinkedHashSet Keepselementsininsertionorder
17 RegularExpressions
17.1 RegularExpressions
Whatareregularexpressions?
• Wordprocessorsusuallyhave find and find/replace.
• Thinkofregularexpressionsasthesamefeatureforstrings, exceptonsteriods.
• Regularexpressionsletyoufindpatternsandthenreplacethem.
• Regularexpressionsarealsocalled regex.
17.2 PatternMatching
Exercise: Detectifastringcontainstheword”good”or”bad”. Ifitcontains”good”replywith”It’sgreatisn’tit?”. Ifitcontains”bad”replywith”It’shorrible. It’shorrible.”
JavaThroughExamples 69
Otherwisesay”Um. Okay.”
Solution:
public static void cleverBot1() {while (true) {
String input =Util.prompt("What's up? ");
if (input.matches(".*\\bgood\\b.*")) {Util.print("It's great isn't it?");
}else if (input.matches(".*\\bbad\\b.*")) {
Util.print("It's horrible. It's horrible.");
}else {
Util.print("Um. Okay.");
}}
}
Notes:
• matches returnstrueiftheregularexpressionmatches input andfalseother-wise.
17.3 RegexSummary
Whatarethemainelementsusedtodefineregularexpressions?
Regex Meaning
. matchesanycharacter
\w matchesalphabet, digit, underscore
\W matcheseverythingbut \w
JavaThroughExamples 70
\d matchesdigitcharacter
\D matchesnon-digitcharacter
\s matchesspacecharacter
\S matchesnon-spacecharacter
\b matchesboundary
\B matchesnon-boundary
[abc] matches a or b or c
[ˆabc] matchesanyletterexcept a or b or c
[-abc] matches a or b or c or -
[a-z] matchesanylowercaseletter
[A-Z] matchesanyuppercaseletter
[a-zA-Z] matchesanyletter
\? matchesquestionmark
\. matchesdot
ˆ matchesbeginningofstring
$ matchesendofstring
X* matches0ormoreof X
X+ matches1ormoreof X
X? matches0or1of X
X*? matches0ormorebutnon-greedy
X+? matches1ormorebutnon-greedy
X{1,3} matches1ormoreupto3of X
X{,3} matches0ormoreupto3of X
X{3,} matches3ormoreof X
X{3} matchesexactly3of X
(?s) enablestreatingstringassingleline, . matchesnewline
(?i) enablescaseinsensitivematching
(?x) allowsspacesandcommentsinregex(# toendoflineignored)
JavaThroughExamples 71
Notes:
• Everyregularexpression \ hastobetypedas \\ inthestring.
17.4 Replace
Exercise: Extendthebot. Anytimeitseesastatementthatstartswith”I am”, itreplaces”I am”with”Whyareyou”. Forexample, ”I amtired”becomes”Whyareyoutired?”.
Solution:
public static void cleverBot2() {while (true) {
String input =Util.prompt("What's up? ");
if (input.matches("I\\s+am\\b.*")) {String output = input.replaceAll(
"^I\\s+am\\b(.*?)\\W*$","Why are you$1?");
}else {
Util.print("Um. Okay.");
}}
}
Notes:
• $1matchesthefirstgroupinparenthesesintheregularexpression. $2matchesthesecondgroup. Andsoon.
17.5 Functions
Whatarethemainstringregexfunctions?
JavaThroughExamples 72
Function Effect
s.matches(regex) Trueif s has regex match
s.replaceAll(regex, replace) Replacesall regex with replace
s.replaceFirst(regex, replace) Replacesfirst regex with replace
s.split(regex) Splits s basedon regex
18 SystemInteraction
18.1 CommandLineArguments
Exercise: Print thenumberofcommandlinearguments thatwaspassedintomain.Thenprintthearguments.
public static void commandLine(String[] args) {System.out.printf(
"args.length = %d\n",args.length);
for (int i = 0 ; i < args.length; ++i) {System.out.printf(
"args[%d] = %s\n",i, args[i]);
}
}
18.2 CapturingCommandOutput
Exercise: Write a program that finds the IP address of a givenhost by calling theprogram nslookup. TestitusingGoogle, Yahoo, eBay, localhost.
Solution:
JavaThroughExamples 73
public static void nslookup() {String hostName =
Util.prompt("Host name: ");String output =
Util.shellExecute("nslookup " + hostName);
String address =output.replaceAll(
"(?s)^.*?Name:.*?\nAddress: (.*?)\n.*$","$1");
Util.print("Address: " + address);}
19 MoreEclipse
19.1 AddingThirdPartyJarFiles
Exercise: AddJSON.simpletothe demo project.
Solution:
• Goto https://code.google.com/p/json-simple/
• Clickon Downloads
• Download json-simple-1.1.1.jar
• Right-clickontheproject
• Select BuildPath --> AddExternalArchives
• Select json-simple-1.1.1.jar
• Totestthatthelibraryisavailable, addthiscodetotheproject
public static void testJson() {Map<String,Object> map =
new LinkedHashMap<String,Object>();
JavaThroughExamples 74
map.put("name","foo");
map.put("number",new Integer(100));
map.put("balance",new Double(1000.21));
map.put("isSpecial",new Boolean(true));
map.put("nickname",null);
String jsonText =JSONValue.toJSONString(map);
System.out.println(jsonText);}
• FiximporterrorsbyclickingCtrl-1(onWindows)orCmd-1(onMac)
Exercise: Exportthisprojectasasinglejarfilewiththedependencies.
Solution:
• Followthesamestepsasearlierforexport. Choosedefaultswherepossible.
• Whenyougetthischoice, choosethefirstoptionwhichisthedefault.
– ExtractrequiredlibrariesintogeneratedJAR– PackagerequiredlibrariesintogeneratedJAR– Copyrequiredlibrariesintosub-foldernexttogeneratedJAR
What is the difference between extract required libraries and package required li-braries?
• Extractrequiredlibraries includestheclassfilesfromthejarfileintoyourjar.Packagerequiredlibraries includestheexternallibrariesasajarinsideyourjar.
• Inbothcasesyouhaveastandalonejar.
• The package optionisusefulifyouwanttomakesuretherearenolicensingissueswithputtingexternalclasseswithyourcode.
JavaThroughExamples 75
19.2 DebuggingUsingBreakPoints
Exercise: Debugthetipcalculatorbysteppingthroughitandinspectingallthevariablevalues.
19.3 Refactorings: Extract-Method, Extract-Variable
Exercise: ExtractvariablesandmethodsfromthesamplecodeintheDemoclass.
20 WebClient
20.1 GettingWebContentFromGET Requests
Exercise: Findoutthesizeofthepageat http://www.google.com
Solution:
public static void webPageSize() {String url =
"http://www.google.com";String html =
Util.webGet(url);System.out.println(
"Size: " + html.length());}
Exercise: Inadditiontothesizeofthepage, findouthowlongittakestodownloadit.
public static void webPageSizeAndTime() {String url =
"http://www.google.com";long startTime =
System.currentTimeMillis();String html =
Util.webGet(url);
JavaThroughExamples 76
long endTime =System.currentTimeMillis();
long totalTime =endTime - startTime;
System.out.println("Size: " + html.length());
System.out.println("Time (ms): " + totalTime);
}
20.2 PassingParameterstoPOST Requests
Exercise: Send a POST request to http://www249.pair.com/asim/tmp/request.php withparametersname, city, andstate, andthenprinttheresponse.
Solution:
public static void webPost() {String url =
"http://www249.pair.com/asim/tmp/request.php";String html =
Util.webPost(url,"name", "Dmitri","city", "Hayward","state", "CA");
System.out.println("HTML: " + html);
}
20.3 RealtimeStockQuotes
Exercise: GetrealtimestockquotesfromYahoo’sJSON webservice.
Solution:
// Define the URL and get JSON.String symbol = "T";
JavaThroughExamples 77
String urlString ="http://finance.yahoo.com"+ "/webservice/v1/symbols/"+ symbol+ "/quote?format=json";
String json = Util.webGet(urlString);
// Convert string to JSON object.JSONObject response = (JSONObject)
JSONValue.parseWithException(json);
// Drill down into the JSON object.JSONObject list = (JSONObject)
response.get("list");JSONArray resources = (JSONArray)
list.get("resources");JSONObject resourcesElement = (JSONObject)
resources.get(0);JSONObject resource = (JSONObject)
resourcesElement.get("resource");JSONObject fields = (JSONObject)
resource.get("fields");String priceString = (String)
fields.get("price");
// Convert price to double.double price = Double.parseDouble(
priceString);System.out.println(
"Price: " + price);
Exercise: Writeastaticfunctioncalled getRealtimeQuote whichtakesastocksym-bolasanargumentandreturnstherealtimestockquoteasadoubleeverytimeitiscalled.
Exercise: Writeaclasscalled RealtimeQuote thattakesastocksymbolinthecon-structorandthenreturnstherealtimestockpriceeverytime get() iscalledonit.
JavaThroughExamples 78
21 DatabaseUsingJDBC
21.1 TestingJDBC
Exercise: Createapersondatabase, inserttworecordsinit, andthenselectthem.
Solution:
• Grabsqlite-jdbc3.7.2fromthislocation https://bitbucket.org/xerial/sqlite-jdbc/downloads/sqlite-jdbc-3.7.2.jar
• IncludethisfileinEclipsebyfollowingthesesteps.
– Right-clickontheproject
– Select BuildPath --> AddExternalArchives
– Select sqlite-jdbc-3.7.2.jar
• Test database operations by adding this code to the project. Change theDB_FILE asappropriateforyourmachine.
private static finalString DB_FILE = "/tmp/sample.db";
private static void testSqlite()throws ClassNotFoundException {
// Load JDBC driver.Class.forName("org.sqlite.JDBC");
Connection connection = null;try {
// Create database connection.connection =
DriverManager.getConnection("jdbc:sqlite:" + DB_FILE);
Statement statement =connection.createStatement();
statement.setQueryTimeout(30);
JavaThroughExamples 79
// Create table.statement.executeUpdate(
"drop table " +"if exists person");
statement.executeUpdate("create table person " +"(id integer, name string)");
statement.executeUpdate("insert into person " +"values(1, 'alice')");
statement.executeUpdate("insert into person " +"values(2, 'bob')");
// Select table.ResultSet rs =
statement.executeQuery("select * from person");
while (rs.next()) {System.out.println(
"name = " +rs.getString("name"));
System.out.println("id = " + rs.getInt("id"));
}}catch(SQLException e) {
System.err.println(e.getMessage());
}finally {
try {if(connection != null)
connection.close();}catch(SQLException e) {
System.err.println(e);}
JavaThroughExamples 80
}}
• FiximporterrorsbyclickingCtrl-1(onWindows)orCmd-1(onMac)
21.2 VerifyingDatabaseContents
Exercise: Installsqlite3shellifyouareonWindows.
Solution:
• Goto http://www.sqlite.org/download.html.
• Findthe PrecompiledBinariesforWindows section.
• Downloadthe sqlite-shell zipfileandunzipittogettheshell.
Exercise: Verifythatthedatabasewascreated.
Solution:
• Runsqlite3onthedatabasefile.
sqlite3 /tmp/sample.db
• Verifythetablecontentsbytypingthisinthesqlite3prompt.
select * from person;
• Quitsqlite3, bytypingthis.
.quit
JavaThroughExamples 81
22 JavaUI
22.1 TipCalculatorwithUI
Exercise: CreatethetipcalculatorwithaUI.
Solution:
public static void tipUI()throws Exception {
JPanel panel = new JPanel(new GridLayout(0,1));
int width = 15;panel.setBorder(
new EmptyBorder(width, width,width, width));
final JTextField amountField =addTextField(panel,
"Amount");final JTextField peopleField =
addTextField(panel,"People");
final JTextField tipRateField =addTextField(panel,
"TipRate");final JLabel resultLabel =
addValueLabel(panel,"Amount Per Person");
JButton submit =new JButton("Calculate");
submit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
JavaThroughExamples 82
try {String output =
getAmountPerPerson(amountField,peopleField,tipRateField);
resultLabel.setText(output);
}catch (NumberFormatException e) {
resultLabel.setText("Invalid input");
}}
});panel.add(submit);
JFrame frame =new JFrame("Tip Calculator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setMinimumSize(new Dimension(200, 300));
frame.getContentPane().add(panel);frame.pack();frame.setVisible(true);
}
private static String getAmountPerPerson(JTextField amountField,JTextField peopleField,JTextField tipRateField) {
double amount =Double.parseDouble(
amountField.getText());int people =
Integer.parseInt(peopleField.getText());
JavaThroughExamples 83
double tipRate =Integer.parseInt(
tipRateField.getText());double amountPerPerson =
amount* (1 + tipRate/100.0)/ people;
String output =String.format(
"$%.2f",amountPerPerson);
return output;}
private static JLabel addValueLabel(JPanel panel, String labelText) {
JLabel valueLabel =new JLabel("");
panel.add(new JLabel(labelText));panel.add(valueLabel);panel.add(new JLabel(""));return valueLabel;
}
private static JTextField addTextField(JPanel panel, String label) {
final JTextField textField =new JTextField("");
panel.add(new JLabel(label));panel.add(textField);panel.add(new JLabel(""));return textField;
}