计算机编程JAVA课堂笔记美国威斯康辛大学麦迪逊分校Word文档下载推荐.docx

计算机编程JAVA课堂笔记美国威斯康辛大学麦迪逊分校Word文档下载推荐.docx

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languageshumansusetocommunicate,whicharefullofambiguity

∙Formallanguages:

preciseandunambiguouslanguagesusedtocommunicatespecificideas

∙Algorithms–basics

∙Howdowedetermineifanalgorithmworksasdesired?

oWecarefullyperformthealgorithmtoseewhatresults.Itworksifwegetthedesiredoutcome

oWecallthistracing

∙Algorithms–execution

∙Weassume:

otheywillstartatthebeginning/top

otheywilldoinstructionsinorder,oneafteranother,formthetoptothebottom（sequencing）

otheywillstopattheend/bottom

∙Algorithms–Criteria

∙Whatmakesitgood:

oItworksasdesired

oItisefficient（takefewersteps）

oItisrobust（handleerrorswell）

oItisuserfriendly

oItisclear（well-structured,well-documented）

oItisgeneral

∙1stJavaProgram:

Class

∙What’saclass?

oItisacontainerforaprogram’scode

oStartclassnameswithanUppercaseletter

File

∙What’safile?

oItisacontainerofrelatedinfothat’skeptinsecondarystorage

main

∙What’samethod?

oItisacontainerforinstructionsthatdoaparticulartaskorsolveaparticularpartofaproblem

oJavaprogramsbeginexecutingatthefirstinstructioninthemainmethodandstopafterexecutingthelastinstructioninmain

Statement

∙What’sastatement?

oIt’sainstruction!

Therearemanydifferentkindsofstatementsandtheyendwithasemicolon;

oItdisplayswhat’sbetweentheparentheses

oprintlnfollowstheoutputwithanewline,whereasprintdoesnot

Developing

∙Eclipse:

oEditing:

enteringtextintoasourcefile（.java）

oCompiling:

translatingthesourcefiletoaclassfile（.class）

oRunning:

usingtheJVMtoexecutetheclassfile

publicclassIRemember{

publicstaticvoidmain（String[]args）

{

System.out.println（"

IRemember!

"

）;

}

}

2ndJavaProgram:

Commenting

∙/*multiline

comment*/

∙//singlelinecomment

∙commentsmakeprogramsmoreunderstandable,butareignoredbythecompiler

∙CS302hasspecificcommentingstandards（seeonlineCS302commentingguide）’

Braces

∙{}:

recallthataclassandamethodarecontainers,Bracesmarkthebeginningandendingofthosecontainers

obody:

what’sbetween{}

oheadings:

whatcomesbefore{

∙makesureeveryopeningbrace{

hasamatchingclosingbrace}

ReservedWords

∙what’sareservedword?

oIt’saworddefinedbythePLtohaveaspecificpurpose

∙Listallofthereservedwordsintheprogramabove:

oPublic,class,static,void

∙Reservedwordscannotbeusedfornamingthings.

identifiers

∙what’sanidentifier?

oIt’sanamewegivetoaclass,amethod,avariable,etc.

∙Listalloftheidentifiersintheprogramabove:

oClasses:

IRemember,String,System

oMethods:

main,println

oVariables:

args,out

∙Whenchoosingidentifiersnamingrulesmustbefollowed（seeonlineCS302styleguide）

Volumes

∙What’savariable?

oIt’sacontainerforasinglevaluethatcanchange

oItcanstoreonlyoneparticulartypeofdata

∙Howdoesthecomputerknowthevariable’stype?

oBeforeavariablecanbeused,itstypeisspecifiedinadeclarationstatement.Theformis:

<

type>

<

listofvariablesseparatedbycommas>

;

∙Byconvention,weputvariabledeclarationstatementsatthebeginningofamethod

NumericDataTypes

∙Ifavariableholdsawholenumber,whattypeshouldbeused?

ointiftherangeofvariableis-2to+2billion

owecalltheseintegers

∙ifavariableholdsarealnumber

odoubleiftherangeofvalueis–3.4*10308to+3.4*10308

owecallthesefloating-pointvariables

3rdJavaProgram:

Variables

∙Howisavariablegivenavalue?

oEitherbyinitializingitinthedeclarationstatementorbyusinganassignmentstatement

∙Whenreadinganassignmentstatementreplacethe=withtheword“gets”.Forexample:

omonth=12;

“monthGETS12”

AssignmentStatements

∙FormoftheAssignmentStatement:

variable>

=<

value,variable,orexpression>

oLHSof=isavariable

oRHSof=canbe:

▪Aliteralvalue:

count=112233;

▪Avariable:

count=numberOfStudents;

▪Anexpression:

count=count+1;

∙CommasareNOTallowedinnumbers!

112,233resultsinacompile-timeerror.

∙Tracingassignmentstatements:

o1.Firstfigureoutthevalueoftheresultontheright

o2.Thenassignthatvaluetothevariableontheleft

MixingNumericTypes

∙Assigninganintegervalueintoafloating-pointvariableworksjustfine:

doubleaccountBalance=1000;

∙Assigningafloating-pointvalueintoanintegervariabledoesNOTwork!

intnumberOfStudents=22.11;

oWhy?

It’sliketryingtocramalargeobjectintoasmallbox.Itdoesn’tfitandthat’sillegal.

oTodothisyoumustuseatypecast:

intnumberOfStudents=（int）22.11;

oDoesthiswork?

intcount=0.0;

No!

Constants

∙What’saconstant?

oIt’sasinglevaluethatCANNOTchange（duringexecution）

oItcaneitherbeanexplicitvalue（calledaliteralorhard-codedconstant）,oritcanbeanamedconstant（justcallaconstant）.

∙Usenamedconstantstomakeyourprogrammoreunderstandableandeasiertoupdate/correct!

∙Examplesofliteralconstants:

11,1234567,-2integerconstants

.009,8.,3.77floating-pointconstants

“string”,“howdy”stringconstants

∙Writenamedconstantfor3.2%interestrate:

finaldoubleINTEREST_RATE=.032;

Form:

final<

CONSTANT_NAME>

value>

∙Allnamedconstantsusethefinalmodifier

whichtellsthecompilerthisisthefinalvalueitgets.

Expressions

∙Expression:

it’sacombinationofoperatorsandoperandsthatisevaluatedtoobtainaresultvalue.

∙Operator:

it’sasymbolthatinstructsthecomputertoperformabasicactionononeormoreoperands.

∙Operand:

it’saliteral,constant,variable,resultfromanotherexpression,avaluereturnedbyamethod,orothersourceofinformation

BasicArithmeticOperators

∙Basicmathematicaloperationsaredefinedforintegerandfloating-pointtypesincluding:

oBinaryoperations:

+,-,*,/,%

oUnaryoperations:

+plussign;

-minussign

∙Divisiondependsonthetypeofoperands!

∙Integersalsohaveremainderdivision（%modulus）

IncrementandDecrementOperators

∙Addingorsubtractingby1arecommonoperations:

ocount=count+1;

//increment

ocount=count–1;

//decrement

∙Instead,usethese（unary）operators:

ocount++;

ocount––;

∙Use++and–instatementsbythemselves（asshown）toavoidconfusingresults

∙Updatingavariablebasedonitsoriginalvalueisanothercommonoperation

Writingprogramsuserfriendly!

∙UserinputmakesourprogramsmoreGENERAL!

∙Algorithmforcalculatingprograms（rectanglearea）:

o1.Getinput（readlengthandwidth）

o2.Calculatetheresult（areaislength*width）

o3.Outputtheresult（displayarea）

∙Thesestatementsconnecttheprogramtothekeyboard:

oimportjava.util.Scanner;

ScannerstdIn=newScanner（System.in）;

∙

owidth=stdIn.nextDouble（）;

olength=stdIn.nextDouble（）;

Input–TheScannerClass

∙Javaprovidesapre-writtenclassnamedScanner,whichallowyoutogetinputfromauser.

∙Threethingsneededtousepre-writtenclasses:

o1.Tellthecompilerwheretogetthecodebyusinganimportstatement:

importjava.util.Scanner;

o2.Makeasoftwareobjectbydeclaringandinitializingit:

o3.Usethesoftwareobjectbycallinmethodslikethese:

=stdIn.nextInt（）;

=stdIn.nextLine（）;

CharacterType–char

∙Acharvariableholdsasinglecharacter（storedasanintegervalue）

∙Acharliteralissurroundedbysinglequotes,like‘B’,1,:

∙Whatisoutputbythiscode:

oCharfirst,middle,last;

oFirst=‘J’;

oMiddle=‘D’;

oLast=‘S’;

oSystem.out.println（“Hello”,+first+middle+last+”!

”）;

StringClass

∙Stringisanotherpre-writtenclassfromwhichwecanmakesoftwareobjects（simplycalledobjects）.Itdoestheworkofstoringanddoingtasksonsequencesofcharacterssuchaswords,phrases,etc.

∙Softwareobjectsmakeprogrammersmoreefficient!

∙TouseStrings:

o1.Wedon’tneedanimportstatement（butcouldhave）:

importjava.lang.String;

//automaticallyimported

o2.WedoneedtomakeaStringobject:

Stringname1=“Deb”;

Stringname2=newString（“Jim”）;

o3.wecanthenaskthestringobjecttodothetask:

∙Stringoperations

oAssignmentandinitializationusing=

oConcatenationusing+

∙StringMethods:

bycallingmethodswecandomanyusefulthingswithstrings

oLength:

returnsthenumberofcharactersinstringobject

Stringname=“EnterFudd”;

System.out.print（name.length（）+“letters”）;

Output?

10letters

och