Java课件第二章补充数组.ppt

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1、Chapter 2 ArrayChapter 2 Array2.1DeclaringandCreatingArrays2.1DeclaringandCreatingArrays2.4CopyingArrays2.4CopyingArrays2.2ArrayInitialize2.2ArrayInitialize2.3Two-demensionArrays2.3Two-demensionArrays2.5PassingArraytomethods2.5PassingArraytomethodsIntroducing ArraysIntroducing ArraysArrayisadatastru

2、cturethatrepresentsacollectionofArrayisadatastructurethatrepresentsacollectionofthesametypesofdata.thesametypesofdata.Declaring Array VariablesDeclaring Array VariablesdatatypedatatypearrayRefVararrayRefVar;Example:Example:doubledoublemyListmyList;datatypedatatype arrayRefVararrayRefVar;/Thisstyleis

3、correct,/Thisstyleiscorrect,butnotpreferredbutnotpreferredExample:Example:doubledoublemyListmyList;v intintaa；=intintaa；v intintaa，b b；intintaa，b b；Creating ArraysCreating ArraysFormat:Format:arrayRefVararrayRefVar=new=newdatatypearraySizedatatypearraySize;Example:Example:myListmyList=newdouble10;=n

4、ewdouble10;DefaultValue:DefaultValue:Whenanarrayiscreated,itselementsareWhenanarrayiscreated,itselementsareassignedthedefaultvalueofassignedthedefaultvalueof 0forthenumericprimitivedatatypes0forthenumericprimitivedatatypesu0000forchartypesu0000forchartypesfalseforbooleantypesfalseforbooleantypesCrea

5、ting ArraysCreating Arrayse.g.:myList.lengthreturns10e.g.:myList.lengthreturns10TheLengthofanArray:TheLengthofanArray:Onceanarrayiscreated,itssizeisfixed.ItOnceanarrayiscreated,itssizeisfixed.Itcannotbechanged.Youcanfinditssizeusingcannotbechanged.YoucanfinditssizeusingarrayRefVar.lengtharrayRefVar.

6、lengthuseusenewnewtocreat:tocreat:c=newchar5c=newchar5；u000u0000 0 u000u0000 0 u000u0000 0 u000u0000 0 u000u0000 05 50 x12340 x1234vv(c ch ha ar r a ar rr ra ay y，5 5 c ch ha ar r d da at ta a )cCreating ArraysCreating ArraysCreatingArrayCreatingArray：I.referencedatatypereferencedatatypeArray:Array:

7、II.Pointp=newPointp=newPoint3Point3；nullnull nullnullnullnull3 30 x12450 x1245vv(P Po oi in nt t A Ar rr ra ay y，3 3 P Po oi in nt t d da at ta a)p pp0p0p1p1p2p2Creating ArraysCreating ArraysII.weshouldusenewtoallocatememoryweshouldusenewtoallocatememoryforeveryelements.foreveryelements.0,00,0p0p00

8、x12450 x1245p p0,00,0nullnull3 30 x24640 x24640 x24660 x2466p1p1p0=newPointp0=newPoint（）；（）；（）；（）；p1=newPointp1=newPoint（）；（）；（）；（）；CreatingArrayCreatingArray：Creating ArraysCreating ArraysDeclaring and Creating in One StepDeclaring and Creating in One StepdatatypedatatypearrayRefVararrayRefVar=new=

9、newdatatypearraySizedatatypearraySize;e.g.:doublee.g.:doublemyListmyList=newdouble10;=newdouble10;datatypedatatype arrayRefVararrayRefVar=new=newdatatypearraySizedatatypearraySize;e.g.:doublee.g.:doublemyListmyList=newdouble10;=newdouble10;0 00 00 03 30 x45670 x4567a ainta=newint3；a0a0a1a1a2a2a.leng

10、tha.lengthExampleExample：Declaring and Creating in One StepDeclaring and Creating in One StepArray InitializeArray InitializeDeclaring,creating,initializinginonestep:e.g.:inta=1e.g.:inta=1，2 2，3 3，4 4，55；Strings=“abc”Strings=“abc”，“def”“def”；Strings=newString(“abc”),Strings=newString(“abc”),newStrin

11、g(“def”);newString(“def”);Thisshorthandsyntaxmustbeinonestatement.doublemyList=1.9,2.9,3.4,3.5;doublemyList=1.9,2.9,3.4,3.5;Thisshorthandnotationisequivalenttothefollowingstatements:doublemyList=newdouble4;doublemyList=newdouble4;myList0=1.9;myList0=1.9;myList1=2.9;myList1=2.9;myList2=3.4;myList2=3.

12、4;myList3=3.5;myList3=3.5;Array InitializeArray InitializeCAUTIONCAUTIONUsingtheshorthandnotation,youhavetodeclare,create,andinitializethearrayallinonestatement.Splittingitwouldcauseasyntaxerror.Forexample,thefollowingiswrong:doublemyList;myList=1.9,2.9,3.4,3.5;ArrayInitialize：Case:Case:ArrayClassOb

13、j.javaArrayClassObj.javaCase:Case:ArrayInit.javaArrayInit.javaArrays Initialize ExampleArrays Initialize Exampleimportjava.util.*;importjava.util.*;publicclassArrayClassObjpublicclassArrayClassObjstaticRandomrand=newRandom();staticRandomrand=newRandom();staticintpRand(intmod)staticintpRand(intmod)re

14、turnMath.abs(rand.nextInt()%mod;returnMath.abs(rand.nextInt()%mod;publicstaticvoidmain(Stringargs)publicstaticvoidmain(Stringargs)Integera=newIntegerpRand(20);Integera=newIntegerpRand(20);prt(lengthofa=+a.length);prt(lengthofa=+a.length);for(inti=0;ia.length;i+)for(inti=0;ia.length;i+)ai=newInteger(

15、pRand(500);ai=newInteger(pRand(500);prt(a+i+=+ai);prt(a+i+=+ai);staticvoidprt(Strings)staticvoidprt(Strings)System.out.println(s);System.out.println(s);ArrayClassObj.javaArrayClassObj.javapublicclassArrayInitpublicclassArrayInitpublicstaticvoidmain(Stringargs)publicstaticvoidmain(Stringargs)Integera

16、=Integera=newInteger(1),newInteger(1),newInteger(2),newInteger(2),newInteger(3),newInteger(3),;/Java1.1only:Integerb=newIntegerIntegerb=newIntegernewInteger(1),newInteger(1),newInteger(2),newInteger(2),newInteger(3),newInteger(3),;Two-dimensional ArraysTwo-dimensional ArraysDeclarearrayDeclarearrayr

17、efvarrefvar:dataTypedataTyperefVarrefVar;e.g.:e.g.:CreatearrayandassignitsreferencetovariableCreatearrayandassignitsreferencetovariablerefVarrefVar=newdataType1010;=newdataType1010;CombinedeclarationandcreationinonestatementCombinedeclarationandcreationinonestatementdataTypedataTyperefVarrefVar=newd

18、ataType1010;=newdataType1010;AlternativesyntaxAlternativesyntaxdataTypedataType refVarrefVar=newdataType1010;=newdataType1010;vv intintaa；vv intintaa；vv intintaa；Two-dimensional Array IllustrationTwo-dimensional Array IllustrationTwo-dimensional ArraysTwo-dimensional ArraysLengthofTwo-dimensionalArr

19、ays:LengthofTwo-dimensionalArrays:e.g.:e.g.:intintx=newint34;x=newint34;Caution:Accessinganarrayoutofboundsisacommonprogrammingerror,whichthrowsaruntimeArrayIndexOutOfBoundsException.Toavoidit,makesurethatyoudonotuseanindexbeyondarrayRefVar.length-1.Two-dimensional ArraysTwo-dimensional Arraysintarr

20、ay=intarray=1,2,3,1,2,3,4,5,6,4,5,6,7,8,9,7,8,9,10,11,1210,11,12;array.lengtharray.lengtharray0.lengtharray0.lengtharray1.lengtharray1.lengtharray2.lengtharray2.lengtharray3.lengtharray3.lengtharray4.lengthArrayIndexOutOfBoundsExceptionarray4.lengthArrayIndexOutOfBoundsExceptionTwo-dimensional Array

21、sTwo-dimensional ArraysExampleExample：CreatingCreating：【e.g.e.g.】inta=newint3inta=newint3；nullnull nullnullnullnull3 30 x49780 x4978a aa0a0a1a1a2a2a.lengtha.lengthTwo-dimensional ArraysTwo-dimensional Arraysnullnull nullnullnullnull3 30 x49780 x4978a aa0a0a1a1a2a2a.lengtha.lengtha=newint3a=newint3；a

22、0=newint3a0=newint3；a00a00a01a01a02a02a0.lengtha0.length0 0 0 00 03 3nullnull nullnullnullnull3 30 x49780 x4978a aa0a0a1a1a2a2a.lengtha.lengtha=newint3a=newint3；a0=newint3a0=newint3；a1=newint2a1=newint2；a00a00a01a01a02a02a0.lengtha0.length0 0 0 00 03 30 00 02 2a10a10a11a11a1.lengtha1.lengthnullnull

23、nullnullnullnull3 30 x49780 x4978a aa0a0a1a1a2a2a.lengtha.lengtha=newint3a=newint3；a0=newint3a0=newint3；a1=newint2a1=newint2；a2=newint4a2=newint4；a00a00a01a01a02a02a0.lengtha0.length0 0 0 00 03 30 00 02 2a10a10a11a11a1.lengtha1.lengtha20a20a21a21a22a22a23a230 00 00 00 04 4a2.lengtha2.lengthDeclaring

24、,Creating,and Initializing Declaring,Creating,and Initializing Using Shorthand Notations Using Shorthand NotationsYoucanalsouseanarrayinitializertodeclare,createYoucanalsouseanarrayinitializertodeclare,createandinitializeatwo-dimensionalarray.Forexample,andinitializeatwo-dimensionalarray.Forexample,

25、intarray=newint43;intarray=newint43;array00=1;array01=2;array02=3;array00=1;array01=2;array02=3;array10=4;array11=5;array12=6;array10=4;array11=5;array12=6;array20=7;array21=8;array22=9;array20=7;array21=8;array22=9;array30=10;array31=11;array32=array30=10;array31=11;array32=12;12;intarrayintarray=1

26、,2,3,1,2,3,4,5,6,4,5,6,7,8,9,7,8,9,10,11,1210,11,12;SameasSameasEnhanced for LoopEnhanced for LoopJDK1.5introducedJDK1.5introducedanewforloopthatenablesyoutotraverseanewforloopthatenablesyoutotraversethecompletearraysequentiallywithoutusinganindexvariable.thecompletearraysequentiallywithoutusinganin

27、dexvariable.Ingeneral,thesyntaxisIngeneral,thesyntaxis YoustillhavetouseanindexvariableifyouwishtotraversetheYoustillhavetouseanindexvariableifyouwishtotraversethearrayinadifferentorderorchangetheelementsinthearray.arrayinadifferentorderorchangetheelementsinthearray.for(elementTypevalue:arrayRefVar)

28、for(elementTypevalue:arrayRefVar)/Processthevalue/Processthevalue Arraytest.javaArraytest.javaStrings=newString10;Strings=newString10;a)Thislineofcodeisillegal.a)Thislineofcodeisillegal.b)sisatwo-dimensionalarraycontainingb)sisatwo-dimensionalarraycontaining10rowsand10columns10rowsand10columnsc)Each

29、elementinsissettoc)Eachelementinsissettod)Eachelementinsisuninitializedandd)Eachelementinsisuninitializedandmustbeinitializedbeforeitisreferenced.mustbeinitializedbeforeitisreferenced.【ExerciseExercise】Copying ArraysCopying ArraysOften,inaprogram,youneedtoduplicateanarrayorOften,inaprogram,youneedto

30、duplicateanarrayorapartofanarray.Insuchcasesyoucouldattempttoapartofanarray.Insuchcasesyoucouldattempttousetheassignmentstatement(=),asfollows:usetheassignmentstatement(=),asfollows:list2=list1;list2=list1;Copying ArraysCopying ArraysUsingaloop:Usingaloop:intsourceArray=2,3,1,5,10;intsourceArray=2,3

31、,1,5,10;inttargetArray=newinttargetArray=newintsourceArray.length;intsourceArray.length;for(inti=0;isourceArrays.length;i+)for(inti=0;isourceArrays.length;i+)targetArrayi=sourceArrayi;targetArrayi=sourceArrayi;The arraycopy UtilityThe arraycopy Utilityvarraycopy(sourceArrayarraycopy(sourceArray,src_

32、possrc_pos,targetArraytargetArray,tar_pos,length);tar_pos,length);Example:Example:System.arraycopy(sourceArraySystem.arraycopy(sourceArray,0,0,targetArraytargetArray,0,0,sourceArray.lengthsourceArray.length););vvCopyingArray:CopyingArray:System.arraycopySystem.arraycopy(object,(object,intint,object,

33、object,intint,intint)intinta=1,2,3;a=1,2,3;intintb=4,5,6,7,8,9;b=4,5,6,7,8,9;System.arraycopySystem.arraycopy(a,0,b,0,a.length);(a,0,b,0,a.length);b=1,2,3,7,8,9;b=1,2,3,7,8,9;Arraycopy.javaArraycopy.javaThe arraycopy UtilityThe arraycopy UtilityPassing Arrays to MethodsPassing Arrays to Methodspubli

34、cstaticvoidprintArray(intarray)publicstaticvoidprintArray(intarray)for(inti=0;iarray.length;i+)for(inti=0;iarray.length;i+)System.out.print(arrayi+);System.out.print(arrayi+);InvokethemethodInvokethemethodintlist=3,1,2,6,4,2;intlist=3,1,2,6,4,2;printArray(list);printArray(list);InvokethemethodInvoke

35、themethodprintArray(newint3,1,2,6,4,2);printArray(newint3,1,2,6,4,2);Anonymous arrayAnonymous ArrayAnonymous ArrayThestatementThestatementprintArray(newint3,1,2,6,4,2);printArray(newint3,1,2,6,4,2);createsanarrayusingthefollowingsyntax:createsanarrayusingthefollowingsyntax:newdataTypeliteral0,.,lite

36、ralk;ThereisnoexplicitreferencevariablefortheThereisnoexplicitreferencevariableforthearray.Sucharrayiscalledanarray.Sucharrayiscalledananonymous arrayanonymous array.Case:Case:VarArgs.javaVarArgs.java classAinti;classAinti;publicclassVarArgspublicclassVarArgsstaticvoidf(Objectx)staticvoidf(Objectx)f

37、or(inti=0;ix.length;i+)for(inti=0;ix.length;i+)System.out.println(xi);System.out.println(xi);publicstaticvoidmain(Stringargs)publicstaticvoidmain(Stringargs)f(newObjectf(newObjectnewInteger(47),newVarArgs(),newInteger(47),newVarArgs(),newFloat(3.14),newDouble(11.11);newFloat(3.14),newDouble(11.11);f

38、(newObjectone,two,three);f(newObjectone,two,three);f(newObjectnewA(),newA(),newA();f(newObjectnewA(),newA(),newA();VarArgs.javaVarArgs.javaPass By ValuePass By ValueJavausespass by valuepass by valuetopassparameterstoamethod.Thereareimportantdifferencesbetweenpassingavalueofvariablesofprimitive data

39、 types and passing primitive data types and passing arraysarrays.vForaparameterofaprimitivetypevalue,theactualvalueispassed.Changingthevalueofthelocalparameterinsidethemethoddoesnotaffectthevalueofthevariableoutsidethemethod.vForaparameterofanarraytype,thevalueoftheparametercontainsareferencetoanarr

40、ay;thisreferenceispassedtothemethod.Anychangestothearraythatoccurinsidethemethodbodywillaffecttheoriginalarraythatwaspassedastheargument.publicclassPassvaluepublicclassPassvaluepublicstaticvoidmain(Stringargs)publicstaticvoidmain(Stringargs)intx=1;intx=1;/xrepresentsanintvalueinty=newint10;inty=newi

41、nt10;/yrepresentsanarrayofintvaluesm(x,y);m(x,y);/InvokemwithargumentsxandySystem.out.println(xis+x);System.out.println(xis+x);System.out.println(y0is+y0);System.out.println(y0is+y0);publicstaticvoidm(intnumber,intnumbers)publicstaticvoidm(intnumber,intnumbers)number=1001;number=1001;/Assignanewvaluetonumbernumbers0=5555;numbers0=5555;/Assignanewvaluetonumbers0 Simple ExampleSimple ExamplePassvalue.javaPassvalue.java