UML Class Diagram - Javatpoint

The class diagram depicts a static view of an application. It represents the types of objects residing in the system and the relationships between them. ⇧SCROLLTOTOP Home Java UML Pandas Python Java SQL Android Cloud JavaScript Servlet JSP Struts2 Spring Quiz Projects InterviewQ Comment Forum Training UMLTutorial UMLTutorial UMLBuildingBlocks UMLArchitecture UMLDiagrams UMLRelationship AssociationvsAggregationvsComposition UMLAssociation UMLDependency UMLGeneralization UMLRealization UMLClassDiagram UMLObjectDiagram UMLComponentDiagram UMLDeploymentDiagram UMLInteractionDiagram UMLUseCaseDiagram UMLSequenceDiagram UMLCollaborationDiagram UMLStateMachineDiagram UMLActivityDiagram UMLTimingDiagram UMLTools next→ ←prev UMLClassDiagram Theclassdiagramdepictsastaticviewofanapplication.Itrepresentsthetypesofobjectsresidinginthesystemandtherelationshipsbetweenthem.Aclassconsistsofitsobjects,andalsoitmayinheritfromotherclasses.Aclassdiagramisusedtovisualize,describe,documentvariousdifferentaspectsofthesystem,andalsoconstructexecutablesoftwarecode. Itshowstheattributes,classes,functions,andrelationshipstogiveanoverviewofthesoftwaresystem.Itconstitutesclassnames,attributes,andfunctionsinaseparatecompartmentthathelpsinsoftwaredevelopment.Sinceitisacollectionofclasses,interfaces,associations,collaborations,andconstraints,itistermedasastructuraldiagram. PurposeofClassDiagrams Themainpurposeofclassdiagramsistobuildastaticviewofanapplication.Itistheonlydiagramthatiswidelyusedforconstruction,anditcanbemappedwithobject-orientedlanguages.ItisoneofthemostpopularUMLdiagrams.Followingarethepurposeofclassdiagramsgivenbelow: Itanalysesanddesignsastaticviewofanapplication. Itdescribesthemajorresponsibilitiesofasystem. Itisabaseforcomponentanddeploymentdiagrams. Itincorporatesforwardandreverseengineering. BenefitsofClassDiagrams Itcanrepresenttheobjectmodelforcomplexsystems. Itreducesthemaintenancetimebyprovidinganoverviewofhowanapplicationisstructuredbeforecoding. Itprovidesageneralschematicofanapplicationforbetterunderstanding. Itrepresentsadetailedchartbyhighlightingthedesiredcode,whichistobeprogrammed. Itishelpfulforthestakeholdersandthedevelopers. VitalcomponentsofaClassDiagram Theclassdiagramismadeupofthreesections: UpperSection:Theuppersectionencompassesthenameoftheclass.Aclassisarepresentationofsimilarobjectsthatsharesthesamerelationships,attributes,operations,andsemantics.Someofthefollowingrulesthatshouldbetakenintoaccountwhilerepresentingaclassaregivenbelow: Capitalizetheinitialletteroftheclassname. Placetheclassnameinthecenteroftheuppersection. Aclassnamemustbewritteninboldformat. Thenameoftheabstractclassshouldbewritteninitalicsformat. MiddleSection:Themiddlesectionconstitutestheattributes,whichdescribethequalityoftheclass.Theattributeshavethefollowingcharacteristics: Theattributesarewrittenalongwithitsvisibilityfactors,whicharepublic(+),private(-),protected(#),andpackage(~). Theaccessibilityofanattributeclassisillustratedbythevisibilityfactors. Ameaningfulnameshouldbeassignedtotheattribute,whichwillexplainitsusageinsidetheclass. LowerSection:Thelowersectioncontainmethodsoroperations.Themethodsarerepresentedintheformofalist,whereeachmethodiswritteninasingleline.Itdemonstrateshowaclassinteractswithdata. Relationships InUML,relationshipsareofthreetypes: Dependency:Adependencyisasemanticrelationshipbetweentwoormoreclasseswhereachangeinoneclasscausechangesinanotherclass.Itformsaweakerrelationship. Inthefollowingexample,Student_NameisdependentontheStudent_Id. Generalization:Ageneralizationisarelationshipbetweenaparentclass(superclass)andachildclass(subclass).Inthis,thechildclassisinheritedfromtheparentclass. Forexample,TheCurrentAccount,SavingAccount,andCreditAccountarethegeneralizedformofBankAccount. Association:Itdescribesastaticorphysicalconnectionbetweentwoormoreobjects.Itdepictshowmanyobjectsarethereintherelationship. Forexample,adepartmentisassociatedwiththecollege. Multiplicity:Itdefinesaspecificrangeofallowableinstancesofattributes.Incaseifarangeisnotspecified,oneisconsideredasadefaultmultiplicity. Forexample,multiplepatientsareadmittedtoonehospital. Aggregation:Anaggregationisasubsetofassociation,whichrepresentshasarelationship.Itismorespecificthenassociation.Itdefinesapart-wholeorpart-ofrelationship.Inthiskindofrelationship,thechildclasscanexistindependentlyofitsparentclass. Thecompanyencompassesanumberofemployees,andevenifoneemployeeresigns,thecompanystillexists. Composition:Thecompositionisasubsetofaggregation.Itportraysthedependencybetweentheparentanditschild,whichmeansifonepartisdeleted,thentheotherpartalsogetsdiscarded.Itrepresentsawhole-partrelationship. Acontactbookconsistsofmultiplecontacts,andifyoudeletethecontactbook,allthecontactswillbelost. AbstractClasses Intheabstractclass,noobjectscanbeadirectentityoftheabstractclass.Theabstractclasscanneitherbedeclarednorbeinstantiated.Itisusedtofindthefunctionalitiesacrosstheclasses.Thenotationoftheabstractclassissimilartothatofclass;theonlydifferenceisthatthenameoftheclassiswritteninitalics.Sinceitdoesnotinvolveanyimplementationforagivenfunction,itisbesttousetheabstractclasswithmultipleobjects. Letusassumethatwehaveanabstractclassnameddisplacementwithamethoddeclaredinsideit,andthatmethodwillbecalledasadrive().Now,thisabstractclassmethodcanbeimplementedbyanyobject,forexample,car,bike,scooter,cycle,etc. HowtodrawaClassDiagram? Theclassdiagramisusedmostwidelytoconstructsoftwareapplications.Itnotonlyrepresentsastaticviewofthesystembutalsoallthemajoraspectsofanapplication.Acollectionofclassdiagramsasawholerepresentsasystem. Somekeypointsthatareneededtokeepinmindwhiledrawingaclassdiagramaregivenbelow: Todescribeacompleteaspectofthesystem,itissuggestedtogiveameaningfulnametotheclassdiagram. Theobjectsandtheirrelationshipsshouldbeacknowledgedinadvance. Theattributesandmethods(responsibilities)ofeachclassmustbeknown. Aminimumnumberofdesiredpropertiesshouldbespecifiedasmorenumberoftheunwantedpropertywillleadtoacomplexdiagram. Notescanbeusedasandwhenrequiredbythedevelopertodescribetheaspectsofadiagram. Thediagramsshouldberedrawnandreworkedasmanytimestomakeitcorrectbeforeproducingitsfinalversion. ClassDiagramExample Aclassdiagramdescribingthesalesordersystemisgivenbelow. UsageofClassdiagrams Theclassdiagramisusedtorepresentastaticviewofthesystem.Itplaysanessentialroleintheestablishmentofthecomponentanddeploymentdiagrams.Ithelpstoconstructanexecutablecodetoperformforwardandbackwardengineeringforanysystem,orwecansayitismainlyusedforconstruction.Itrepresentsthemappingwithobject-orientedlanguagesthatareC++,Java,etc.Classdiagramscanbeusedforthefollowingpurposes: Todescribethestaticviewofasystem. Toshowthecollaborationamongeveryinstanceinthestaticview. Todescribethefunctionalitiesperformedbythesystem. Toconstructthesoftwareapplicationusingobject-orientedlanguages. 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