Chapter17:StringBuilder

Section17.1:WhataStringBuilderisandwhentouseone

AStringBuilderrepresentsaseriesofcharacters,whichunlikeanormalstring,aremutable.Oftentimesthereisa needtomodifystringsthatwe’vealreadymade,butthestandardstringobjectisnotmutable.Thismeansthateach timeastringismodified,anewstringobjectneedstobecreated,copiedto,andthenreassigned.

stringmyString=”Apples”;

mystring+=”aremyfavoritefruit”;

Intheaboveexample,myStringinitiallyonlyhasthevalue”Apples”.However,whenweconcatenate`”aremy favoritefruit”‘,whatthestringclassdoesinternallyneedstodoinvolves:

• CreatinganewarrayofcharactersequaltothelengthofmyStringandthenewstringweareappending.
• CopyingallofthecharactersofmyStringintothebeginningofournewarrayandcopyingthenewstringinto the end of the array.
• CreateanewstringobjectinmemoryandreassignittomyString.

For a single concatenation, this is relatively trivial. However, what if needed to perform many append operations, say, in a loop?

StringmyString=””;

for(inti=0;i<10000;i++)

myString+=””;//puts10,000spacesintoourstring

Duetotherepeatedcopyingandobjectcreation,thiswillbringsignificantlydegradetheperformanceofour program. We can avoid this by instead using a StringBuilder.

StringBuildermyStringBuilder=newStringBuilder();

for(inti=0;i<10000;i++)

myStringBuilder.Append(”);

Nowwhenthesameloopisrun,theperformanceandspeedoftheexecutiontimeoftheprogramwillbe significantlyfasterthanusinganormalstring.TomaketheStringBuilderbackintoanormalstring,wecansimply call the ToString()method of StringBuilder.

However,thisisn’ttheonlyoptimizationStringBuilderhas.Inordertofurtheroptimizefunctions,wecantake advantageofotherpropertiesthathelpimproveperformance.

StringBuildersb=newStringBuilder(10000);//initializesthecapacityto10000

IfweknowinadvancehowlongourStringBuilderneedstobe,wecanspecifyitssizeaheadoftime,whichwill preventitfromneedingtoresizethecharacterarrayithasinternally.

sb.Append(‘k’,2000);

ThoughusingStringBuilderforappendingismuchfasterthanastring,itcanrunevenfasterifyouonlyneedto addasinglecharactermanytimes.

Onceyouhavecompletedbuildingyourstring,youmayusetheToString()methodontheStringBuilderto convert it to a basic string. This is often necessary because the StringBuilderclass does not inherit from string.

Forexample,hereishowyoucanuseaStringBuildertocreateastring:

stringRepeatCharacterTimes(charcharacter,inttimes)

{

StringBuilderbuilder=newStringBuilder(“”);for(intcou

nter=0;counter<times;counter++)

{

//AppendoneinstanceofthecharactertotheStringBuilder.

builder.Append(character);

}

//Converttheresulttostringandreturnit.

returnbuilder.ToString();

}

Inconclusion,StringBuildershouldbeusedinplaceofstringwhenmanymodificationstoastringneedtobe madewithperformanceinmind.

Section17.2:UseStringBuildertocreatestringfromalarge number of records

publicstringGetCustomerNamesCsv()

{

List<CustomerData>customerDataRecords=GetCustomerData();//Returnsalargenumberof records,say,10000+

StringBuildercustomerNamesCsv=newStringBuilder(); foreach(CustomerDatarecordincustomerDataRecords)

{

customerNamesCsv

.Append(record.LastName)

.Append(‘,’)

.Append(record.FirstName)

.Append(Environment.NewLine);

}

returncustomerNamesCsv.ToString();

}