access modifiers - wikipedia, the free encyclopedia

3/18/2015 AccessmodifiersWikipedia,thefreeencyclopedia

http://en.wikipedia.org/wiki/Access_modifiers 1/3

AccessmodifiersFromWikipedia,thefreeencyclopedia

Accessmodifiers(oraccessspecifiers)arekeywordsinobjectorientedlanguagesthatsettheaccessibilityofclasses,methods,andothermembers.Accessmodifiersareaspecificpartofprogramminglanguagesyntaxusedtofacilitatetheencapsulationofcomponents.[1]

InC++,thereareonlythreeaccessmodifiers.C#extendsthenumberofthemtofive,whileJavahasfouraccessmodifiers,[2]butthreekeywordsforthispurpose.InJava,havingnokeywordbeforedefaultstothepackageprivatemodifier.Accessspecifiersforclasses:Whenaclassisdeclaredaspublic,itisaccessibletootherclassesdefinedinthesamepackageaswellasthosedefinedinotherpackages.Thisisthemostcommonlyusedspecifierforclasses.Aclasscannotbedeclaredasprivate.Ifnoaccessspecifierisstated,thedefaultaccessrestrictionswillbeapplied.Theclasswillbeaccessibletootherclassesinthesamepackagebutwillbeinaccessibletoclassesoutsidethepackage.Whenwesaythataclassisinaccessible,itsimplymeansthatwecannotcreateanobjectofthatclassordeclareavariableofthatclasstype.Theprotectedaccessspecifiertoocannotbeappliedtoaclass.

Contents

1Namesofkeywords2ExampleinC++3References

3.1Notes3.2Bibliography

Namesofkeywords

C++usesthethreemodifierscalledpublic,protected,andprivate.C#hasthemodifierspublic,protected,internal,private,andprotectedinternal.Javahaspublic,package,protected,andprivate.Theaccessmodifierpackageisthedefaultandused,ifanyotheraccessmodifierkeywordismissing.ThisisnotthecaseinC++,whereanabsencemeansthattheobjectisaccessedprivately.Themeaningofthesemodifiersmaydifferfromonelanguagetoanother.Acomparisonofthekeywords,orderedfromthemostrestrictivetothemostopen,andtheirmeaninginthesethreelanguagesfollows.Theirvisibilityrangesfromthesameclasstothepackagewheretheclassisdefinedtoageneralaccesspermission.Below,themaximalaccessiswrittenintothetable.

3/18/2015 AccessmodifiersWikipedia,thefreeencyclopedia

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Keyword C# C++ Javaprivate class class class

protectedinternalsameassemblyandderivedclasses

protected derivedclasses derivedclassesderivedclassesand/orwithinsamepackage

package withinitspackagepublicinternal sameassembly public everybody everybody everybody

ExampleinC++

#includeusingstd::cout;usingstd::endl;structB{//defaultaccessmodifierinsidestructispublicvoidset_n(intv){n=v;}voidf(){cout

3/18/2015 AccessmodifiersWikipedia,thefreeencyclopedia

http://en.wikipedia.org/wiki/Access_modifiers 3/3

References

Notes

1. Mayo2002,pp.199.2. http://javapapers.com/corejava/accessmodifiersinjavaexplain/

Bibliography

Mayo,Joseph(2002),CSharpUnleashed(http://books.google.co.uk/books?id=XdHYaEIl9gC),Samspublishing,ISBN9780672321221

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