




版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
MoreConditionalsandLoopsNowwecanfillinsomeadditionaldetailsregardingJavaconditionalandrepetitionstatementsChapter6focuseson:theswitchstatementtheconditionaloperatorthedolooptheforloopdrawingwiththeaidofconditionalsandloopsdialogboxesOutlineTheswitch
StatementTheConditionalOperatorThedo
StatementThefor
StatementDrawingwithLoopsandConditionalsDialogBoxesTheswitchStatementTheswitchstatementprovidesanotherwaytodecidewhichstatementtoexecutenextTheswitchstatementevaluatesanexpression,thenattemptstomatchtheresulttooneofseveralpossiblecasesEachcasecontainsavalueandalistofstatementsTheflowofcontroltransferstostatementassociatedwiththefirstcasevaluethatmatchesTheswitchStatementThegeneralsyntaxofaswitchstatementis:switch(expression){casevalue1
:
statement-list1casevalue2
:
statement-list2casevalue3:
statement-list3
case
...}switchandcasearereservedwordsIfexpressionmatchesvalue2,controljumpstohereTheswitchStatementOftenabreakstatementisusedasthelaststatementineachcase'sstatementlistAbreakstatementcausescontroltotransfertotheendoftheswitchstatementIfabreakstatementisnotused,theflowofcontrolwillcontinueintothenextcaseSometimesthismaybeappropriate,butoftenwewanttoexecuteonlythestatementsassociatedwithonecaseTheswitchStatementswitch(option){case'A':aCount++;break;
case'B':bCount++;break;case'C':cCount++;break;}Anexampleofaswitchstatement:TheswitchStatementAswitchstatementcanhaveanoptionaldefaultcaseThedefaultcasehasnoassociatedvalueandsimplyusesthereservedworddefaultIfthedefaultcaseispresent,controlwilltransfertoitifnoothercasevaluematchesIfthereisnodefaultcase,andnoothervaluematches,controlfallsthroughtothestatementaftertheswitchTheswitchStatementThetypeofaswitchexpressionmustbeintegers,characters,orenumeratedtypesAsofJava7,aswitchcanalsobeusedwithstringsYoucannotuseaswitchwithfloatingpointvaluesTheimplicitbooleanconditioninaswitchstatementisequalityYoucannotperformrelationalcheckswithaswitchstatementSeeGradeReport.java//********************************************************************//GradeReport.javaAuthor:Lewis/Loftus////Demonstratestheuseofaswitchstatement.//********************************************************************importjava.util.Scanner;publicclassGradeReport{
////Readsagradefromtheuserandprintscommentsaccordingly.//
publicstaticvoidmain(String[]args){
intgrade,category;Scannerscan=newScanner(System.in);System.out.print("Enteranumericgrade(0to100):");grade=scan.nextInt();category=grade/10;System.out.print("Thatgradeis");continuecontinue
switch(category){
case10:System.out.println("aperfectscore.Welldone.");
break;
case9:System.out.println("wellaboveaverage.Excellent.");
break;
case8:System.out.println("aboveaverage.Nicejob.");
break;
case7:System.out.println("average.");
break;
case6:System.out.println("belowaverage.Youshouldseethe");System.out.println("instructortoclarifythematerial"+"presentedinclass.");
break;
default:System.out.println("notpassing.");}}}continue
switch(category){
case10:System.out.println("aperfectscore.Welldone.");
break;
case9:System.out.println("wellaboveaverage.Excellent.");
break;
case8:System.out.println("aboveaverage.Nicejob.");
break;
case7:System.out.println("average.");
break;
case6:System.out.println("belowaverage.Youshouldseethe");System.out.println("instructortoclarifythematerial"+"presentedinclass.");
break;
default:System.out.println("notpassing.");}}}SampleRunEnteranumericgrade(0to100):91Thatgradeiswellaboveaverage.Excellent.OutlineTheswitch
StatementTheConditionalOperatorThedo
StatementThefor
StatementDrawingwithLoopsandConditionalsDialogBoxesTheConditionalOperatorTheconditionaloperatorevaluatestooneoftwoexpressionsbasedonabooleanconditionItssyntaxis:condition?expression1:expression2Ifthecondition
istrue,expression1
isevaluated;ifitisfalse,expression2
isevaluatedThevalueoftheentireconditionaloperatoristhevalueoftheselectedexpressionTheConditionalOperatorTheconditionaloperatorissimilartoanif-elsestatement,exceptthatitisanexpressionthatreturnsavalueForexample: larger=((num1>num2)?num1:num2);Ifnum1isgreaterthannum2,thennum1isassignedtolarger;otherwise,num2isassignedtolargerTheconditionaloperatoristernarybecauseitrequiresthreeoperandsTheConditionalOperatorAnotherexample:Ifcount
equals1,the"Dime"isprintedIfcountisanythingotherthan1,then"Dimes"isprintedSystem.out.println("Yourchangeis"+count+((count==1)?"Dime":"Dimes"));QuickCheckExpressthefollowinglogicinasuccinctmannerusingtheconditionaloperator.if(val<=10)System.out.println("Itisnotgreaterthan10.");elseSystem.out.println("Itisgreaterthan10.");QuickCheckExpressthefollowinglogicinasuccinctmannerusingtheconditionaloperator.if(val<=10)System.out.println("Itisnotgreaterthan10.");elseSystem.out.println("Itisgreaterthan10.");System.out.println("Itis"+((val<=10)?"not":"")+"greaterthan10.");OutlineTheswitch
StatementTheConditionalOperatorThedo
StatementThefor
StatementDrawingwithLoopsandConditionalsDialogBoxesThedoStatementAdostatementhasthefollowingsyntax: do {
statement-list; } while(condition);
Thestatement-list
isexecutedonceinitially,andthenthecondition
isevaluatedThestatementisexecutedrepeatedlyuntiltheconditionbecomesfalseLogicofadoLooptrueconditionevaluatedstatementfalseThedoStatementAnexampleofadoloop:Thebodyofado
loopexecutesatleastonceSeeReverseNumber.javaintcount=0;do{count++;System.out.println(count);}while(count<5);//********************************************************************//ReverseNumber.javaAuthor:Lewis/Loftus////Demonstratestheuseofadoloop.//********************************************************************importjava.util.Scanner;publicclassReverseNumber{
////Reversesthedigitsofanintegermathematically.//
publicstaticvoidmain(String[]args){
intnumber,lastDigit,reverse=0;Scannerscan=newScanner(System.in);continuecontinue
System.out.print("Enterapositiveinteger:");number=scan.nextInt();
do{lastDigit=number%10;reverse=(reverse*10)+lastDigit;number=number/10;}
while(number>0);System.out.println("Thatnumberreversedis"+reverse);}}continue
System.out.print("Enterapositiveinteger:");number=scan.nextInt();
do{lastDigit=number%10;reverse=(reverse*10)+lastDigit;number=number/10;}
while(number>0);System.out.println("Thatnumberreversedis"+reverse);}}SampleRunEnterapositiveinteger:2896Thatnumberreversedis6982ComparingwhileanddostatementtruefalseconditionevaluatedThewhileLooptrueconditionevaluatedstatementfalseThedoLoopOutlineTheswitch
StatementTheConditionalOperatorThedo
StatementThefor
StatementDrawingwithLoopsandConditionalsDialogBoxesTheforStatementAforstatementhasthefollowingsyntax:for(initialization;condition;increment)
statement;TheinitializationisexecutedoncebeforetheloopbeginsThestatement
isexecuteduntiltheconditionbecomesfalseTheincrement
portionisexecutedattheendofeachiterationLogicofaforloopstatementtrueconditionevaluatedfalseincrementinitializationTheforStatementAforloopisfunctionallyequivalenttothefollowingwhileloopstructure:initialization;while(condition){
statement;
increment;}TheforStatementAnexampleofaforloop: for(intcount=1;count<=5;count++) System.out.println(count);TheinitializationsectioncanbeusedtodeclareavariableLikeawhileloop,theconditionofaforloopistestedpriortoexecutingtheloopbodyTherefore,thebodyofaforloopwillexecutezeroormoretimesTheforStatementTheincrementsectioncanperformanycalculation: for(intnum=100;num>0;num-=5) System.out.println(num);AforloopiswellsuitedforexecutingstatementsaspecificnumberoftimesthatcanbecalculatedordeterminedinadvanceSeeMultiples.javaSeeStars.java//********************************************************************//Multiples.javaAuthor:Lewis/Loftus////Demonstratestheuseofaforloop.//********************************************************************importjava.util.Scanner;publicclassMultiples{
////Printsmultiplesofauser-specifiednumberuptoauser-//specifiedlimit.//
publicstaticvoidmain(String[]args){
finalintPER_LINE=5;
intvalue,limit,mult,count=0;Scannerscan=newScanner(System.in);System.out.print("Enterapositivevalue:");value=scan.nextInt();continuecontinue
System.out.print("Enteranupperlimit:");limit=scan.nextInt();System.out.println();System.out.println("Themultiplesof"+value+"between"+value+"and"+limit+"(inclusive)are:");
for(mult=value;mult<=limit;mult+=value){System.out.print(mult+"\t");//Printaspecificnumberofvaluesperlineofoutputcount++;
if(count%PER_LINE==0)System.out.println();}}}continue
System.out.print("Enteranupperlimit:");limit=scan.nextInt();System.out.println();System.out.println("Themultiplesof"+value+"between"+value+"and"+limit+"(inclusive)are:");
for(mult=value;mult<=limit;mult+=value){System.out.print(mult+"\t");//Printaspecificnumberofvaluesperlineofoutputcount++;
if(count%PER_LINE==0)System.out.println();}}}SampleRunEnterapositivevalue:7Enteranupperlimit:400Themultiplesof7between7and400(inclusive)are:7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 161 168 175 182 189 196 203 210 217 224 231 238 245 252 259 266 273 280 287 294 301 308 315 322 329 336 343 350 357 364 371 378 385 392 399//********************************************************************//Stars.javaAuthor:Lewis/Loftus////Demonstratestheuseofnestedforloops.//********************************************************************publicclassStars{
////Printsatriangleshapeusingasterisk(star)characters.//
publicstaticvoidmain(String[]args){
finalintMAX_ROWS=10;
for(introw=1;row<=MAX_ROWS;row++){
for(intstar=1;star<=row;star++)System.out.print("*");System.out.println();}}}//********************************************************************//Stars.javaAuthor:Lewis/Loftus////Demonstratestheuseofnestedforloops.//********************************************************************publicclassStars{
////Printsatriangleshapeusingasterisk(star)characters.//
publicstaticvoidmain(String[]args){
finalintMAX_ROWS=10;
for(introw=1;row<=MAX_ROWS;row++){
for(intstar=1;star<=row;star++)System.out.print("*");System.out.println();}}}Output*******************************************************QuickCheckWriteacodefragmentthatrollsadie100timesandcountsthenumberoftimesa3comesup.QuickCheckWriteacodefragmentthatrollsadie100timesandcountsthenumberoftimesa3comesup.Diedie=newDie();intcount=0;for(intnum=1;num<=100;num++)if(die.roll()==3)count++;Sytem.out.println(count);TheforStatementEachexpressionintheheaderofaforloopisoptionalIftheinitializationisleftout,noinitializationisperformedIftheconditionisleftout,itisalwaysconsideredtobetrue,andthereforecreatesaninfiniteloopIftheincrementisleftout,noincrementoperationisperformedFor-eachLoopsAvariantoftheforloopsimplifiestherepetitiveprocessingofitemsinaniteratorForexample,supposebookListisanArrayList<Book>
objectThefollowingloopwillprinteachbook: for(BookmyBook:bookList) System.out.println(myBook);Thisversionofaforloopisoftencalledafor-eachloopFor-eachLoopsAfor-eachloopcanbeusedonanyobjectthatimplementstheIterable
interfaceIteliminatestheneedtoretrieveaniteratorandcallthehasNextandnextmethodsexplicitlyItalsowillbehelpfulwhenprocessingarrays,whicharediscussedinChapter8QuickCheckWriteafor-eachloopthatprintsalloftheStudentobjectsinanArrayList<Student>objectcalledroster.QuickCheckWriteafor-eachloopthatprintsalloftheStudentobjectsinanArrayList<Student>objectcalledroster.for(Studentstudent:roster)System.out.println(student);OutlineTheswitch
StatementTheConditionalOperatorThedo
StatementThefor
StatementDrawingwithLoopsandConditionalsDialogBoxesDrawingTechniquesConditionalsandloopsenhanceourabilitytogenerateinterestinggraphicsSeeBullseye.javaSeeBullseyePanel.javaSeeBoxes.javaSeeBoxesPanel.java//********************************************************************//Bullseye.javaAuthor:Lewis/Loftus////Demonstratestheuseofloopstodraw.//********************************************************************importjavax.swing.JFrame;publicclassBullseye{
////Createsthemainframeoftheprogram.//
publicstaticvoidmain(String[]args){JFrameframe=newJFrame("Bullseye");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);BullseyePanelpanel=newBullseyePanel();frame.getContentPane().add(panel);frame.pack();frame.setVisible(true);}}//********************************************************************//Bullseye.javaAuthor:Lewis/Loftus////Demonstratestheuseofloopstodraw.//********************************************************************importjavax.swing.JFrame;publicclassBullseye{
////Createsthemainframeoftheprogram.//
publicstaticvoidmain(String[]args){JFrameframe=newJFrame("Bullseye");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);BullseyePanelpanel=newBullseyePanel();frame.getContentPane().add(panel);frame.pack();frame.setVisible(true);}}//********************************************************************//BullseyePanel.javaAuthor:Lewis/Loftus////Demonstratestheuseofconditionalsandloopstoguidedrawing.//********************************************************************importjavax.swing.JPanel;importjava.awt.*;publicclassBullseyePanelextendsJPanel{
privatefinalintMAX_WIDTH=300,NUM_RINGS=5,RING_WIDTH=25;
////Setsupthebullseyepanel.//
publicBullseyePanel(){setBackground(Color.cyan);setPreferredSize(newDimension(300,300));
}continuecontinue////Paintsabullseyetarget.//
publicvoidpaintComponent(Graphicspage){
super.paintComponent(page);
intx=0,y=0,diameter=MAX_WIDTH;page.setColor(Color.white);
for(intcount=0;count<NUM_RINGS;count++){
if(page.getColor()==Color.black)//alternatecolorspage.setColor(Color.white);
elsepage.setColor(Color.black);page.fillOval(x,y,diameter,diameter);diameter-=(2*RING_WIDTH);x+=RING_WIDTH;y+=RING_WIDTH;}//Drawtheredbullseyeinthecenterpage.setColor(Color.red);page.fillOval(x,y,diameter,diameter);}}//********************************************************************//Boxes.javaAuthor:Lewis/Loftus////Demonstratestheuseofloopstodraw.//********************************************************************importjavax.swing.JFrame;publicclassBoxes{
////Createsthemainframeoftheprogram.//
publicstaticvoidmain(String[]args){JFrameframe=newJFrame("Boxes");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);BoxesPanelpanel=newBoxesPanel();frame.getContentPane().add(panel);frame.pack();frame.setVisible(true);}}//********************************************************************//Boxes.javaAuthor:Lewis/Loftus////Demonstratestheuseofloopstodraw.//********************************************************************importjavax.swing.JFrame;publicclassBoxes{
////Createsthemainframeoftheprogram.//
publicstaticvoidmain(String[]args){JFrameframe=newJFrame("Boxes");frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);BoxesPanelpanel=newBoxesPanel();frame.getContentPane().add(panel);frame.pack();frame.setVisible(true);}}//********************************************************************//BoxesPanel.javaAuthor:Lewis/Loftus////Demonstratestheuseofconditionalsandloopstoguidedrawing.//********************************************************************importjavax.swing.JPanel;importjava.awt.*;importjava.util.Random;publicclassBoxesPanelextendsJPanel{
privatefinalintNUM_BOXES=50,THICKNESS=5,MAX_SIDE=50;
privatefinalintMAX_X=350,MAX_Y=250;
privateRandomgenerator;
////Setsupthedrawingpanel.//
publicBoxesPanel(){generator=newRandom();setBackground(Color.black);setPreferredSize(newDimension(400,300));
}continuecontinue////Paintsboxesofrandomwidthandheightinarandomlocation.//Narroworshortboxesarehighlightedwithafillcolor.//
publicvoidpaintComponent(Graphicspage){
super.paintComponent(page);
intx,y,width,height;
for(intcount=0;count<NUM_BOXES;count++){x=generator.nextInt(MAX_X)+1;y=generator.nextInt(MAX_Y)+1;width=generator.nextInt(MAX_SIDE)+1;height=generator.nextInt(MAX_SIDE)+1;continuecontinue
if(width<=THICKNESS)//checkfornarrowbox{page.setColor(Color.yellow);page.fillRect(x,y,width,height);}
else
if(height<=THICKNESS)//checkforshortbox{page.setColor(Color.green);page.fillRect(x,y,width,height);}
else
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 郑州房屋收费管理办法
- 绥化浴池节能管理办法
- 道具专项采购管理办法
- 肺功能不全教学课件
- 手工装裱培训课件
- 肝脓肿护理教学课件
- 高淳区初二数学试卷
- 东师附中初一数学试卷
- 固安县小升初数学试卷
- 商场装修管理培训课件
- 甘肃机电职业技术学院招聘事业编制工作人员笔试真题2024
- 2025-2030中国非晶硅(无定形硅)行业发展规划与供需趋势预测报告
- 人教版(2024)七年级下册英语期末复习:阅读理解 突破练习题(含答案)
- 乙肝肝硬化教学查房课件
- 新生儿皮肤清洁与护理
- 保山2025年云南保山市中心血站招聘编外工作人员笔试题库附带答案详解
- 抢险队伍及物资管理制度
- 弘扬家风文化班会课件
- 吐鲁番采油厂玉果油田滚动建产工程环境影响报告书
- 2025年6月英语四级真题及参考答案
- 浙江省2024-2025学年高二下学期数学学考模拟考(三)(含答案)
评论
0/150
提交评论