计算机软件及应用JAVA程序设计教程第七版第6章课件

Chapter6

MoreConditionalsandLoopsJavaSoftwareSolutionsFoundationsofProgramDesignSeventhEditionChapter6

MoreConditionalsanMoreConditionalsandLoopsNowwecanfillinsomeadditionaldetailsregardingJavaconditionalandrepetitionstatementsChapter6focuseson:theswitchstatementtheconditionaloperatorthedolooptheforloopdrawingwiththeaidofconditionalsandloopsdialogboxesMoreConditionalsandLoopsNowOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementTheswitchStatementTheswitchstatementprovidesanotherwaytodecidewhichstatementtoexecutenextTheswitchstatementevaluatesanexpression,thenattemptstomatchtheresulttooneofseveralpossiblecasesEachcasecontainsavalueandalistofstatementsTheflowofcontroltransferstostatementassociatedwiththefirstcasevaluethatmatchesTheswitchStatementTheswitchTheswitchStatementThegeneralsyntaxofaswitchstatementis:switch(expression){casevalue1

:

statement-list1casevalue2

:

statement-list2casevalue3:

statement-list3

case

...}switchandcasearereservedwordsIfexpressionmatchesvalue2,controljumpstohereTheswitchStatementThegeneraTheswitchStatementOftenabreakstatementisusedasthelaststatementineachcase'sstatementlistAbreakstatementcausescontroltotransfertotheendoftheswitchstatementIfabreakstatementisnotused,theflowofcontrolwillcontinueintothenextcaseSometimesthismaybeappropriate,butoftenwewanttoexecuteonlythestatementsassociatedwithonecaseTheswitchStatementOftenabrTheswitchStatementswitch(option){case'A':aCount++;break;

case'B':bCount++;break;case'C':cCount++;break;}Anexampleofaswitchstatement:TheswitchStatementswitch(opTheswitchStatementAswitchstatementcanhaveanoptionaldefaultcaseThedefaultcasehasnoassociatedvalueandsimplyusesthereservedworddefaultIfthedefaultcaseispresent,controlwilltransfertoitifnoothercasevaluematchesIfthereisnodefaultcase,andnoothervaluematches,controlfallsthroughtothestatementaftertheswitchTheswitchStatementAswitchsTheswitchStatementThetypeofaswitchexpressionmustbeintegers,characters,orenumeratedtypesAsofJava7,aswitchcanalsobeusedwithstringsYoucannotuseaswitchwithfloatingpointvaluesTheimplicitbooleanconditioninaswitchstatementisequalityYoucannotperformrelationalcheckswithaswitchstatementSeeGradeReport.javaTheswitchStatementThetypeo//********************************************************************//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");continue//****************************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.");}}}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.");}}}SampleRunEnteranumericgrade(0to100):91Thatgradeiswellaboveaverage.Excellent.continueSampleRunOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementTheConditionalOperatorTheconditionaloperatorevaluatestooneoftwoexpressionsbasedonabooleanconditionItssyntaxis:condition?expression1:expression2Ifthecondition

istrue,expression1

isevaluated;ifitisfalse,expression2

isevaluatedThevalueoftheentireconditionaloperatoristhevalueoftheselectedexpressionTheConditionalOperatorThecoTheConditionalOperatorTheconditionaloperatorissimilartoanif-elsestatement,exceptthatitisanexpressionthatreturnsavalueForexample: larger=((num1>num2)?num1:num2);Ifnum1isgreaterthannum2,thennum1isassignedtolarger;otherwise,num2isassignedtolargerTheconditionaloperatoristernarybecauseitrequiresthreeoperandsTheConditionalOperatorThecoTheConditionalOperatorAnotherexample:Ifcountequals1,the"Dime"isprintedIfcountisanythingotherthan1,then"Dimes"isprintedSystem.out.println("Yourchangeis"+count+((count==1)?"Dime":"Dimes"));TheConditionalOperatorAnotheQuickCheckExpressthefollowinglogicinasuccinctmannerusingtheconditionaloperator.if(val<=10)System.out.println("Itisnotgreaterthan10.");elseSystem.out.println("Itisgreaterthan10.");QuickCheckExpressthefollowiQuickCheckExpressthefollowinglogicinasuccinctmannerusingtheconditionaloperator.if(val<=10)System.out.println("Itisnotgreaterthan10.");elseSystem.out.println("Itisgreaterthan10.");System.out.println("Itis"+((val<=10)?"not":"")+"greaterthan10.");QuickCheckExpressthefollowiOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementThedoStatementAdostatementhasthefollowingsyntax: do {

statement-list; } while(condition);

Thestatement-list

isexecutedonceinitially,andthenthecondition

isevaluatedThestatementisexecutedrepeatedlyuntiltheconditionbecomesfalseThedoStatementAdostatementLogicofadoLooptrueconditionevaluatedstatementfalseLogicofadoLooptrueconditioThedoStatementAnexampleofadoloop:ThebodyofadoloopexecutesatleastonceSeeReverseNumber.javaintcount=0;do{count++;System.out.println(count);}while(count<5);ThedoStatementAnexampleof//********************************************************************//ReverseNumber.javaAuthor:Lewis/Loftus////Demonstratestheuseofadoloop.//********************************************************************importjava.util.Scanner;publicclassReverseNumber{

////Reversesthedigitsofanintegermathematically.//

publicstaticvoidmain(String[]args){

intnumber,lastDigit,reverse=0;Scannerscan=newScanner(System.in);continue//****************************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);}}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);}}SampleRunEnterapositiveinteger:2896Thatnumberreversedis6982continueSampleRunComparingwhileanddostatementtruefalseconditionevaluatedThewhileLooptrueconditionevaluatedstatementfalseThedoLoopComparingwhileanddostatemenOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementTheforStatementAforstatementhasthefollowingsyntax:for(initialization;condition;increment)

statement;TheinitializationisexecutedoncebeforetheloopbeginsThestatement

isexecuteduntiltheconditionbecomesfalseTheincrement

portionisexecutedattheendofeachiterationTheforStatementAforstatemeLogicofaforloopstatementtrueconditionevaluatedfalseincrementinitializationLogicofaforloopstatementtrTheforStatementAforloopisfunctionallyequivalenttothefollowingwhileloopstructure:initialization;while(condition){

statement;

increment;}TheforStatementAforloopisTheforStatementAnexampleofaforloop: for(intcount=1;count<=5;count++) System.out.println(count);TheinitializationsectioncanbeusedtodeclareavariableLikeawhileloop,theconditionofaforloopistestedpriortoexecutingtheloopbodyTherefore,thebodyofaforloopwillexecutezeroormoretimesTheforStatementAnexampleofTheforStatementTheincrementsectioncanperformanycalculation: for(intnum=100;num>0;num-=5) System.out.println(num);AforloopiswellsuitedforexecutingstatementsaspecificnumberoftimesthatcanbecalculatedordeterminedinadvanceSeeMultiples.javaSeeStars.javaTheforStatementTheincrement//********************************************************************//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();continue//****************************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();}}}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();}}}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 399continueSampleRun//********************************************************************//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.QuickCheckWriteacodefragmeQuickCheckWriteacodefragmentthatrollsadie100timesandcountsthenumberoftimesa3comesup.Diedie=newDie();intcount=0;for(intnum=1;num<=100;num++)if(die.roll()==3)count++;Sytem.out.println(count);QuickCheckWriteacodefragmeTheforStatementEachexpressionintheheaderofaforloopisoptionalIftheinitializationisleftout,noinitializationisperformedIftheconditionisleftout,itisalwaysconsideredtobetrue,andthereforecreatesaninfiniteloopIftheincrementisleftout,noincrementoperationisperformedTheforStatementEachexpressiFor-eachLoopsAvariantoftheforloopsimplifiestherepetitiveprocessingofitemsinaniteratorForexample,supposebookListisanArrayList<Book>objectThefollowingloopwillprinteachbook: for(BookmyBook:bookList) System.out.println(myBook);Thisversionofaforloopisoftencalledafor-eachloopFor-eachLoopsAvariantoftheFor-eachLoopsAfor-eachloopcanbeusedonanyobjectthatimplementstheIterableinterfaceIteliminatestheneedtoretrieveaniteratorandcallthehasNextandnextmethodsexplicitlyItalsowillbehelpfulwhenprocessingarrays,whicharediscussedinChapter8For-eachLoopsAfor-eachloopQuickCheckWriteafor-eachloopthatprintsalloftheStudentobjectsinanArrayList<Student>objectcalledroster.QuickCheckWriteafor-eachloQuickCheckWriteafor-eachloopthatprintsalloftheStudentobjectsinanArrayList<Student>objectcalledroster.for(Studentstudent:roster)System.out.println(student);QuickCheckWriteafor-eachloOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementDrawingTechniquesConditionalsandloopsenhanceourabilitytogenerateinterestinggraphicsSeeBullseye.javaSeeBullseyePanel.javaSeeBoxes.javaSeeBoxesPanel.javaDrawingTechniquesConditionals//********************************************************************//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));

}continue//****************************continue////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);}}continue//********************************************************************//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));

}continue//****************************continue////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;continuecontinuecontinue

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{page.setColor(Color.white);page.drawRect(x,y,width,height);}}}}continueOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementDialogBoxesAdialogboxisawindowthatappearsontopofanycurrentlyactivewindowItmaybeusedto:conveyinformationconfirmanactionallowtheusertoenterdatapickacolorchooseafileAdialogboxusuallyhasaspecific,solitarypurpose,andtheuserinteractionwithitisbriefDialogBoxesAdialogboxisaDialogBoxesTheJOptionPaneclassprovidesmethodsthatsimplifythecreationofsometypesofdialogboxesSeeEvenOdd.javaSpecializeddialogboxesforchoosingcolorsandfilesarecoveredinChapter9DialogBoxesTheJOptionPanecl/********************************************************************//EvenOdd.javaAuthor:Lewis/Loftus////DemonstratestheuseoftheJOptionPaneclass.//********************************************************************importjavax.swing.JOptionPane;publicclassEvenOdd{

////Determinesifthevalueinputbytheuserisevenorodd.//Usesmultipledialogboxesforuserinteraction.//

publicstaticvoidmain(String[]args){StringnumStr,result;

intnum,again;continue/*****************************continue

do{numStr=JOptionPane.showInputDialog("Enteraninteger:");num=Integer.parseInt(numStr);result="Thatnumberis"+((num%2==0)?"even":"odd");JOptionPane.showMessageDialog(null,result);again=JOptionPane.showConfirmDialog(null,"DoAnother?");}

while(again==JOptionPane.YES_OPTION);}}continuecontinue

do{numStr=JOptionPane.showInputDialog("Enteraninteger:");num=Integer.parseInt(numStr);result="Thatnumberis"+((num%2==0)?"even":"odd");JOptionPane.showMessageDialog(null,result);again=JOptionPane.showConfirmDialog(null,"DoAnother?");}

while(again==JOptionPane.YES_OPTION);}}continueSummaryChapter6focusedon:theswitchstatementtheconditionaloperatorthedolooptheforloopdrawingwiththeaidofconditionalsandloopsdialogboxesSummaryChapter6focusedon:Chapter6

MoreConditionalsandLoopsJavaSoftwareSolutionsFoundationsofProgramDesignSeventhEditionChapter6

MoreConditionalsanMoreConditionalsandLoopsNowwecanfillinsomeadditionaldetailsregardingJavaconditionalandrepetitionstatementsChapter6focuseson:theswitchstatementtheconditionaloperatorthedolooptheforloopdrawingwiththeaidofconditionalsandloopsdialogboxesMoreConditionalsandLoopsNowOutlineTheswitch

StatementTheConditionalOperatorThedo

StatementThefor

StatementDrawingwithLoopsandConditionalsDialogBoxesOutlineTheswitchStatementTheswitchStatementTheswitchstatementprovidesanotherwaytodecidewhichstatementtoexecutenextTheswitchstatementevaluatesanexpression,thenattemptstomatchtheresulttooneofseveralpossiblecasesEachcasecontainsavalueandalistofstatementsTheflowofcontroltransferstostatementassociatedwiththefirstcasevaluethatmatchesTheswitchStatementTheswitchTheswitchStatementThegeneralsyntaxofaswitchstatementis:switch(expression){casevalue1

:

statement-list1casevalue2

:

statement-list2casevalue3:

statement-list3

case

...}switchandcasearereservedwordsIfexpressionmatchesvalue2,controljumpstohereTheswitchStatementThegeneraTheswitchStatementOftenabreakstatementisusedasthelaststatementineachcase'sstatementlistAbreakstatementcausescontroltotransfertotheendoftheswitchstatementIfabreakstatementisnotused,theflowofcontrolwillcontinueintothenextcaseSometimesthismaybeappropriate,butoftenwewanttoexecuteonlythestatementsassociatedwithonecaseTheswitchStatementOftenabrTheswitchStatementswitch(option){case'A':aCount++;break;

case'B':bCount++;break;case'C':cCount++;break;}Anexampleofaswitchstatement:TheswitchStatementswitch(opTheswitchStatementAswitchstatementcanhaveanoptionaldefaultcaseThedefaultcasehasnoassociatedvalu