Charcater and Strings.ppt Charcater and Strings.ppt

new

1. Characters and Strings

2. •TheJavaplatformcontainsthreeclasses
1.Character:-Aclasswhoseinstancescanholdasingle
charactervalue
2.String:-Aclassforworkingwithimmutable
(unchanging)datacomposedofmultiplecharacters
3.StringBuffer:-Aclassforstoringandmanipulating
mutabledatacomposedofmultiplecharacters.
•Character
–useaCharacterobjectinsteadofaprimitivecharvariable
whenanobjectisrequired
–Forexample,whenpassingacharactervalueintoa
method

3. publicclassCharacterDemo{
publicstaticvoidmain(Stringargs[]){
Charactera=newCharacter('A');
Charactera2=newCharacter('a');
Characterb=newCharacter('b');
intdifference=a.compareTo(b);
if(difference==0){
System.out.println(a+"isequalto"+b);
}
elseif(difference<0)
System.out.println(a+"islessthan"+b);
else
System.out.println(a+"isgreaterthan"+b);

4. System.out.println(a+"is"+((a.equals(a2))?"equal":"not
equal")+"to"+a2);
System.out.println("Thecharacter"+a.toString()+"is"+
(Character.isUpperCase(a.charValue())?"upper":
"lower")+"case.");
}
}
•Output
–Aislessthanb
–Aisnotequaltoa
–ThecharacterAisuppercase.

5. Character Class
•Constant
–publicstaticfinalintMAX_RADIX=36
–publicstaticfinalcharMAX_VALUE=‘\ffff’
–publicstaticfinalintMIN_RADIX=2
–publicstaticfinalcharMIN_VALUE=’\0000’
•Method
–Character(charvalue):Constructortoinitializethe
objectasvalue
–charcharValue():Convertintochartype
–staticbooleanisDigit(charch):Testwhetherisdigit?
–staticbooleanisLetter(charch):Testwhetherisletter?
–staticbooleanisLetterOrDigit(charch):Returnwhenit
isletterordigit.

6. •String
–InJavaastringisasequenceofcharacters
–JavaimplementsstringsasobjectsoftypeString.
–objectsoftypeStringareimmutable;
–onceaStringobjectiscreated,itscontentscannotbealtered
–IfyouwanttochangeStringobject
•createanewstringthatcontainsthemodifications.
•UseStringBufferclass
–Stringscanbeconstructedavarietyofways.
•useastatementlike:
StringmyString="thisisatest";
•usingthenewkeywordandaconstructor
–Forexample:Stringstr=newString(charArray);
–BothStringandStringBufferaredeclaredfinal,which
meansthatneitheroftheseclassesmaybesubclassed.

7. •Stringsareimmutable
classStringTest{
publicstaticvoidmain(Stringargs[]){
Stringname=“Kebede”;
System.out.println(name);
name=name+“Tollosa”;
System.out.println(name);
}
}
•OutPut:
Kebede
KebedeTollosa
Memory
name Kebede
Kebede Tollosa

8. The String Constructors
•TheStringclasssupportsseveralconstructors.
Strings=newString();
–TocreateaStringinitializedbyanarrayofcharacters,usethe
constructor
String(charchars[])
–example:
charchars[]={'a','b','c'};
Strings=newString(chars);
–Thisconstructorinitializesswiththestring"abc".
–Youcanspecifyasub-rangeofacharacterarrayasan
initializerusingthefollowingconstructor:
String(charchars[],intstartIndex,intnumChars)
–startIndexspecifiestheindexatwhichthesubrangebegins,
andnumCharsspecifiesthenumberofcharacterstouse

9. –example:
charchars[]={'a','b','c','d','e','f'};
Strings=newString(chars,2,3);
–Thisinitializesswiththecharacterscde.
–YoucanconstructaStringobjectthatcontainsthesame
charactersequenceasanotherStringobjectusingthis
constructor:
String(StringstrObj)
–example:
classMakeString{
publicstaticvoidmain(Stringargs[]){
charc[]={'J','a','v','a'};
Strings1=newString(c);
Strings2=newString(s1);
System.out.println(s1);
System.out.println(s2);
}}

10. –Theoutputfromthisprogramisasfollows:
Java
Java
–Thefollowingprogramconvertsthegivenbytearrayinto
String
//Constructstringfromsubsetofchararray.
classSubStringCons{
publicstaticvoidmain(Stringargs[]){
byteascii[]={65,66,67,68,69,70};
Strings1=newString(ascii);
System.out.println(s1);
Strings2=newString(ascii,2,3);
System.out.println(s2);
}}
–Thisprogramgeneratesthefollowingoutput:
ABCDEF
CDE

11. String Class
•Method
–charcharAt(intindex):
•Returnthecharacteratspecificpositioninstring
–intlength():
•Returnthelengthofstring
–StringtoUpperCase():
•Convertthestringintouppercharacter
–StringtoLowerCase():
•Convertthestringintolowercharacter
–voidgetChars():
•extractmorethanonecharacteratatime
–Stringsubstring(intbeginIndex):
•MakethesubstringfrombeginIndextotheendofthe
string

12. •getChars()
–extractmorethanonecharacteratatime
–generalform:
voidgetChars(intStart,intEnd,chartarget[],inttargetStart)
–Startspecifiestheindexofthebeginningofthesubstring,
–Endspecifiesanindexthatisonepasttheendofthedesired
substring
–Thearraythatwillreceivethecharactersisspecifiedbytarget.
–Theindexwithintargetatwhichthesubstringwillbecopiedis
passedintargetStart

13. –ThefollowingprogramdemonstratesgetChars():
classgetCharsDemo{
publicstaticvoidmain(Stringargs[]){
Strings="ThisisademoofthegetCharsmethod.";
intstart=10;
intend=14;
charbuf[]=newchar[end-start];
s.getChars(start,end,buf,0);
System.out.println(buf);
}
}
–Hereistheoutputofthisprogram:
demo

14. •StringConcatenation
–+operator
–Example:
Stringage="9";
Strings="Heis"+age+"yearsold.";
System.out.println(s);
•StringConcatenationwithOtherDataTypes
intage=9;
Strings="Heis"+age+"yearsold.";
System.out.println(s);
–Thecompilerwillconvertanoperandtoitsstringequivalent
whenevertheotheroperandofthe+isaninstanceofString.

15. –Considerthefollowing:
Strings="four:"+2+2;
System.out.println(s);
–Thisfragmentdisplays
four:22
–Tocompletetheintegeradditionfirst,youmustuse
parentheses,likethis:
Strings="four:"+(2+2);
–Nowscontainsthestring"four:4".
•Youcanconcatenatetwostringsusingconcat()
Stringconcat(Stringstr)
Strings1="one";
Strings2=s1.concat("two");

16. •StringConversionandtoString()
–Javaconvertsdataintoitsstringrepresentationduring
concatenationby
•callingoneofthestringconversionmethodvalueOf()
•valueOf()isoverloadedforallthesimpletypesandfortype
Object
–Forthesimpletypes,valueOf()returnsastringthatcontains
thehuman-readableequivalentofthevaluewithwhichitis
called.
–Forobjects,valueOf()callsthetoString()methodonthe
object
–EveryclassimplementstoString()becauseitisdefinedby
Object
–ThetoString()methodhasthisgeneralform:
StringtoString()

17. •ThefollowingprogramdemonstratesoverridingtoString()
fortheBoxclass:
//OverridetoString()forBoxclass.
classBox{
doublewidth,height,depth;
Box(doublew,doubleh,doubled){
width=w;
height=h;
depth=d;
}
publicStringtoString(){
return"Dimensionsare"+width+"by"+depth+"by"
+height+".";
}
}

18. classtoStringDemo{
publicstaticvoidmain(Stringargs[]){
Boxb=newBox(10,12,14);
Strings="Boxb:"+b;//concatenateBoxobject
System.out.println(b);//convertBoxtostring
System.out.println(s);
}
}
–Theoutputofthisprogramisshownhere:
Dimensionsare10by14by12.
Boxb:Dimensionsare10by14by12

19. //AbubblesortforStrings.
classSortString{
staticStringarr[]={"Now","is","the","time","for","all",
"good",“persons","to","come","to","the","aid","of","their",
"country”};
publicstaticvoidmain(Stringargs[]){
for(intj=0;j<arr.length;j++){
for(inti=j+1;i<arr.length;i++){
if(arr[i].compareTo(arr[j])<0){
Stringt=arr[j];
arr[j]=arr[i];
arr[i]=t;
}
}
System.out.println(arr[j]);
}
}}

20. •SearchingStrings
–TheStringclassprovidestwomethodsthatallowyouto
searchastringforaspecifiedcharacterorsubstring:
–indexOf()Searchesforthefirstoccurrenceofacharacteror
substring.
–lastIndexOf()Searchesforthelastoccurrenceofacharacter
orsubstring.
–Tosearchforthefirstorlastoccurrenceofasubstring,use
intindexOf(Stringstr)
intlastIndexOf(Stringstr)
–strspecifiesthesubstring
–Youcanspecifyastartingpointforthesearchusingthese
forms:
intindexOf(chaech,intstartIndex)
intlastIndexOf(charch,intstartIndex)
intindexOf(Stringstr,intstartIndex)
intlastIndexOf(Stringstr,intstartIndex)

21. •ForindexOf(),thesearchrunsfromstartIndextotheendof
thestring.
•ForlastIndexOf(),thesearchrunsfromstartIndextozero.
//DemonstrateindexOf()andlastIndexOf().
classindexOfDemo{
publicstaticvoidmain(Stringargs[]){
Strings="Nowisthetimeforallgoodpersons"+"tocometo
theaidoftheircountry.";
System.out.println(s);
System.out.println("indexOf(t)="+s.indexOf('t'));
System.out.println("lastIndexOf(t)="+s.lastIndexOf('t'));
System.out.println("indexOf(the)="+s.indexOf("the"));
System.out.println("lastIndexOf(the)="+s.lastIndexOf("the"));

22. System.out.println("indexOf(t,10)="+s.indexOf('t',10));
System.out.println("lastIndexOf(t,60)="+s.lastIndexOf('t',60));
System.out.println("indexOf(the,10)="+s.indexOf("the",10));
System.out.println("lastIndexOf(the, 60)=“+s.lastIndexOf("the",60));
}
}
–theoutputofthisprogram:
Nowisthetimeforallgoodmentocometotheaidoftheircountry.
•Nowisthetimeforallgoodpersonstocometotheaidof
theircountry.
indexOf(t)=7 lastIndexOf(t)=68
indexOf(the)=7 lastIndexOf(the)=58
indexOf(t,10)=11 lastIndexOf(t,60)=58
indexOf(the,10)=47 lastIndexOf(the,60)=58

23. •ModifyingaString
–tomodifyaString,youmusteithercopyitintoa
StringBufferoruseoneofthefollowingStringmethods,
–substring()
•Ithastwoforms.
1.Stringsubstring(intstartIndex)
2.Stringsubstring(intstartIndex,intendIndex)
•Thestringreturnedcontainsallthecharactersfromthe
beginningindex,upto,butnotincluding,theendingindex.

24. //Substringreplacement.
classStringReplace{
publicstaticvoidmain(Stringargs[]){
Stringorg="Thisisatest.Thisis,too.";
Stringsearch="is";
Stringsub="was";
Stringresult="";
inti;
do{//replaceallmatchingsubstrings
System.out.println(org);
i=org.indexOf(search);
if(i!=-1){
result=org.substring(0,i);
result=result+sub;

25. result=result+org.substring(i+search.length());
org=result;
}//endofif
}while(i!=-1);
}
}
•Theoutput
Thisisatest.Thisis,too.
Thwasisatest.Thisis,too.
Thwaswasatest.Thisis,too.
Thwaswasatest.Thwasis,too.
Thwaswasatest.Thwaswas,too.

26. Exercise
•Writeaprogramthatperformsthefollowing
–Acceptsastring
–convertsitintoUppercaseorLowercase
–extractsubstringbasedontheusersinterest.
–SearchaPalindromewordwithinthegivenstring.
–countsthenumberofwords
–Extractthespecialcharacters

27. StringBuffer Class
•isapeerclassofString
•representsgrowableandwriteablecharactersequences.
•willautomaticallygrowtomakeroomforsuchadditions
•oftenhasmorecharacterspre-allocatedthanareactually
needed,toallowroomforgrowth.
–forexample,whenreadingtextdatafromafile.
•mayhavecharactersandsubstringsinsertedinthemiddleor
appendedtotheend.
•StringBufferdefinesthesethreeconstructors:
–StringBuffer()
–StringBuffer(intsize)
–StringBuffer(Stringstr)

28. •Thedefaultconstructor(theonewithnoparameters)
reservesroomfor16characterswithoutreallocation.
•Thesecondversionacceptsanintegerargumentthat
explicitlysetsthesizeofthebuffer.
•ThethirdversionacceptsaStringargumentthatsetsthe
initialcontentsoftheStringBufferobjectandreservesroom
for16morecharacterswithoutreallocation.
•Byallocatingroomforafewextracharacters,StringBuffer
reducesthenumberofreallocationsthattakeplace.

29. •length()andcapacity()
–ThecurrentlengthofaStringBuffercanbefoundviathe
length()method
–Thetotalallocatedcapacitycanbefoundthroughthe
capacity()method.
•Hereisanexample:
//StringBufferlength
classStringBufferDemo1{
publicstaticvoidmain(Stringargs[]){
StringBuffersb=newStringBuffer("Hello");
System.out.println("buffer="+sb);
System.out.println("length="+sb.length());
System.out.println("Capacity="+sb.capacity());
}}
•Output:buffer=Hello
length=5 Capacity=21

30. •append()
–Theappend()methodconcatenatesthestringrepresentationof
anyothertypeofdatatotheendoftheinvokingStringBuffer
object
–fewofitsforms:
StringBufferappend(Stringstr)
StringBufferappend(intnum)
StringBufferappend(Objectobj)

31. //Demonstrateappend().
classappendDemo{
publicstaticvoidmain(Stringargs[]){
Strings;
inta=42;
StringBuffersb=newStringBuffer(40);
s=sb.append("a=").append(a).append("!").toString();
System.out.println(s);
}
}
•Theoutputofthisexampleisshownhere:
a=42!

32. •insert()
–Theinsert()methodinsertsonestringintoanother
–fewofitsforms:
StringBufferinsert(intindex,Stringstr)
StringBufferinsert(intindex,charch)
StringBufferinsert(intindex,Objectobj)
//Demonstrateinsert().
classinsertDemo{
publicstaticvoidmain(Stringargs[]){
StringBuffersb=newStringBuffer("IJava!");
sb.insert(2,"like");
System.out.println(sb);
}
}
–Theoutput
IlikeJava!

33. •reverse()
StringBufferreverse()
//Usingreverse()toreverseaStringBuffer.
classReverseDemo{
publicstaticvoidmain(Stringargs[]){
StringBuffers=newStringBuffer("abcdef");
System.out.println(s);
s.reverse();
System.out.println(s);
}
}
–theoutput:
abcdef
fedcba

34. •delete()anddeleteCharAt()
–Thedelete()methoddeletesasequenceofcharactersfromthe
invokingobject.
StringBufferdelete(intstartIndex,intendIndex)
–startIndexspecifiestheindexofthefirstcharactertoremove,
andendIndexspecifiesanindexonepastthelastcharacterto
remove.
–thesubstringdeletedrunsfromstartIndextoendIndex–1.
StringBufferdeleteCharAt(intloc)
–deletesthecharacterattheindexspecifiedbyloc.

35. //Demonstratedelete()anddeleteCharAt()
classdeleteDemo{
publicstaticvoidmain(Stringargs[]){
StringBuffersb=newStringBuffer("Thisisatest.");
sb.delete(4,7);
System.out.println("Afterdelete:"+sb);
sb.deleteCharAt(0);
System.out.println("AfterdeleteCharAt:"+sb);
}
}
–Theoutput:
Afterdelete:Thisatest.
AfterdeleteCharAt:hisatest.

36. •replace()
–replacesonesetofcharacterswithanothersetinsidea
StringBufferobject.
StringBufferreplace(intstartIndex,intendIndex,Stringstr)
//Demonstratereplace()
classreplaceDemo{
publicstaticvoidmain(Stringargs[]){
StringBuffersb=newStringBuffer("Thisisatest.");
sb.replace(5,7,"was");
System.out.println("Afterreplace:"+sb);
}
}
–Theoutput:
Afterreplace:Thiswasatest.

37. StringBuffer Class
String now = new java.util.Date().toString();
StringBufferstrbuf= new StringBuffer(now);
strbuf.append(" : ").append(now.length()).append('.');
System.out.println(strbuf.toString());