2023学年完整公开课版javastatements

Statements//commentcontentsinglelinecomment/*...commentcontent....*/multi-linecomments/**...commentcontent....*/textcommentsStatements

compound

statementscontrolstatementsmethodcallstatementsexpressionstatements2134canuse{}toenclosesomestatementstoformcompoundstatementsSystem.out.println(“Hello”);controlstatementsincludeconditionalbranchstatements,loopstatementsandjumpstatementsaddthesemicolonaftertheexpressionExecutablestatementInputStatementsInputandoutputaremainlyintheJava.iopackage,learnlaterStandardinputandoutputintheSystemClass,encapsulatedinJava.langSystemClasshas3constantsfortheinputandoutputofthesysteminStandardinputstream,whichmainlyprocessesdatainputfromkeyboardorotherinputdevicesout

Standardoutputstream,whichmainlyoutputsdatatothedisplayorotheroutputterminalserr

Standardoutputstream,mainlyoutputerrorinformationOutputdatatotheconsole:System.out.println();//wrapSystem.out.print();

//notwrapInputdatafromthekeyboard:ScannerClassScannerin=newScanner(System.in);Commonmethods：StringnextLine()Stringnext()intnextInt()doublenextDouble()booleannextBoolean()BasicProgramStructurecyclicstructureselectionstructuresequencestructure123refertotheexecutionofonebyoneintheorderinwhichthestatementsintheprogrambaseontheresultofconditionaljudgment,chooseoneoftwoormorepathstoexecuterepeatasetofoperationswithmultipletimesThreeBasicStructuresifStatementsProblem

Intheobject-orientedprogramming,whataretheclassicusesofif

statementsinJava?Writeaprogram,inputtwointegersfromthekeyboard,andoutputthelargervalueofthesetwonumbers.Howtoachievethis?

ifStatementsif…elseif…elseifUnbalancedif020103Unbalancedifif（expression）{statements;}

Theexpressionisaconditionaljudgmentexpression,thestatementscanbethecompoundstatements,andtheentirestructureisastatement.expressionstatementstruefalseUnbalancedifforexample：Inputtwointegersfromthekeyboard,andoutputthelargervalueofthesetwonumbers.max<bmax=btruefalsemax=aif(max<b){max=b;}if…elseif(expression)statement1；elsestatement2；expressionstatement1truefalsestatement2if…elseforexample：Inputtwointegersfromthekeyboard,andoutputthelargervalueofthesetwonumbers.a>bmax=atruefalsemax=bif…elseifexpression1expression2expression3expression(n)statement(n+1)statement(n)statement3statement2statement1falsefalsefalsefalsetruetruetruetrueif(expression1)statement1;elseif(expression2)statement2;… … …elseif(expressionn)statement(n);elsestatement(n+1);Example:JudgewhethertheinputcharacterisanEnglishletter,number,spaceorother.letternumberspaceotherjudge

whetherthecharacteristheletterjudge

whetherthecharacteristhespacejudge

whetherthecharacteristhenumber||ch>=‘0’&&ch<=‘9’ch==''letterspacenumberif…elseifch>='a'&&ch<='z'ch>='A'&&ch<='Z'

Writeaprogram,inputthreeintegersfromthekeyboard,andoutputthemaximumvalueofthesethreenumbers.Howtoachievethis?PracticeSwitch

StatementsProblemInobject-orientedprogramming,howtousetheswitchstatementinJava?

Enterapercentilescore,andoutputgradesof'A’,'B’,'C',and'D'arerequired.Amongthem,90pointsormoreisA,70-89pointsisB,60-69pointsisC,and60pointsorlessisD.switch(expression){ caseconstantexpression1：<statement1>;<break;> caseconstantexpression2：<statement2>;<break;> … … … … caseconstantexpression(n)：<statement(n)>;<break;> <default:statement(n+1)>;}

Thepartenclosedinthepairofanglebracketsisoptional.explanationSwitchString,int,enumExampleForexample：Enterapercentilescore,andoutputgradesof'A’,'B’,'C',and'D'arerequired.Amongthem,90pointsormoreisA,70-89pointsisB,60-69pointsisC,and60pointsorlessisD.a10090-9970-8960-6960orlessAnalysis:a/101097、866orless【Practice】Inputanynumberbetween1-7,theprogramwilloutputthecorrespondingdayoftheweekinEnglishaccordingtotheuser'sinput.Forexample,input3andtheprogramwilloutputWednesday.Ifyououtputanumberotherthan1-7,itwillpromptaninputerror!PracticeforCyclicStatementsProblemInobject-orientedprogramming,howtousetheforstatementinJava?Writeaprogramtofind1+2+3+……+100.forStatements

for(expression1;expression2;expression3)

loopbody;（1）solvingexpression1（2）judgmentloopconditionexpression2

Ifthevalueofexpression1istrue,executethestatementintheloopbody,andthenexecutestep(3);Ifthevalueisfalse,thenjumpoutoftheloopandexecutestep(5).（3）solvingexpression3（4）jumpbacktostep(2)andrepeat（5）aftertheloopfinished,executethefollowingstatementoftheloopbodycalculateexpression1judgeexpression2loopbodycalculateexpression3truefalseforStatementsFormat

for(expression1;expression2;expression3)

loopbody;计算表达式1判断表达式2循环体计算表达式3truefalseloopbody：

repeatedoperationexpression1：初始化条件，表示最初的状态expression2：判断条件，表示在什么情况下结束循环expression3：控制条件，控制初始化条件的变化s=0+1Example:writeaprogram,ask1+2+3+……+100。Example+2+3+4+……+100Loopbody:operationsperformedrepeatedlyExpression1:Initializationcondition,whichrepresentstheinitialstate.Expression2:Judgmentcondition,indicatingtheendoftheloopunderwhatcircumstances.Expression3:Controlcondition,controlthechangeofinitializationcondition.s=s+is=0i=1i<=100i++Accumulator,theinitialvalueis0.PrecautionsforusingtheforstatementsThethreeexpressionsintheforstatementcanbeomitted,butthe";"cannotbeomitted.Ifexpression1isomitted,theloopvariableshouldbeassignedaninitialvaluebeforetheforstatement.Ifexpression2isomitted,theloopwillfallintoaninfiniteloop,andthedetectionandexitloopmechanismshouldbearrangedelsewhere.Ifexpression3isomitted,theworkthatmakesthelooptendtoendshouldbearrangedelsewhere.NoteExpression1;

for(;;){

loopbody;

//addtheexitloopmechanismhere

expression3;}

for(expression1;expression2;expression3)

loopbody;whileanddo-whileloopProblemInobject-orientedprogramming,thedifferencebetweenwhileanddowhilestatementsinJava?Writeaprogramtofind1+2+3+……+100.Grammaticalformatwhile(expression){statementsequence;}whilestatementSolvetheloopconditionalexpression,ifthevalueistrue,gotostep2;ifthevalueisfalse,thenjumpoutoftheloopandgotostep4.Executethestatementinsidetheloopbodyofthewhilestatement.Jumpbacktostep1andrepeatexecution.executethestatementfollowingthebodyofthewhileloop.DescriptionwhilestatementLoopbody:operationsperformedrepeatedlyInitializationcondition:indicatestheinitialstateJudgmentcondition:IndicatestheendoftheloopunderwhatcircumstancesControlconditions:controlchangesininitializationconditions

expression1;

while（expression2){

loopbody;

expression3;}

for(expression1;expression2;expression3)

loopbody;whilestatementIssuesneedingattentionwhenusingthewhilestatement：theloopbodyshouldbewrittenintheformofcompoundsentencesavoid"endlessloops"020103thewhileloopjudgesfirstandthenloopsGrammaticalformatdo{statementsequence;}while(expression);do…whilestatementExecutethesequenceofstatementsinsidethebodyofthestatementloop.Solvetheloopconditionexpression,ifthevalueistrue,repeatstep1;otherwise,jumpoutoftheloopandexecutestep3.Executethestatementfollowingthebodyofthewhileloop.Descriptionatleastoncedo{statementsequence;}while(expression);while(expression){statementsequence;}do…whilestatementJumpstatementbreakstatementGrammaticalformatbreak;Terminatetheexecutionoftheswitchstatementorloopstatement(jumpoutofthesetwostatements),andmovetothesubsequentstatementforexecution.Effection一:break实例continuestatementGrammaticalformatcontinue;Endthiscycle.Thatis,sk