C# Class and Objects - TutorialsTeacher

A class can contain one or more constructors, fields, methods, properties, delegates, and events. They are called class members. A class and its members can ... 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Forexample,acarshouldhavesomeattributessuchasfourwheels,twoormoredoors,steering,awindshield,etc. Itshouldalsohavesomefunctionalitieslikestart,stop,run,move,etc. Now,anyobjectthathastheseattributesandfunctionalitiesisacar. Here,thecarisaclassthatdefinessomespecificattributesandfunctionalities.Eachindividualcarisanobjectofthecarclass. Youcansaythatthecaryouarehavingisanobjectofthecarclass. Likewise,inobject-orientedprogramming,aclassdefinessomeproperties,fields,events,methods,etc.Aclassdefinesthekindsofdataandthefunctionalitytheirobjectswillhave. DefineaClass InC#,aclasscanbedefinedbyusingtheclasskeyword. Let'sdefineaclassnamed'Student'. Example:DefineaClass classStudent { } Aclasscancontainoneormoreconstructors,fields,methods,properties,delegates,andevents.Theyarecalledclassmembers. Aclassanditsmemberscanhaveaccessmodifierssuchaspublic,private,protected,andinternal,torestrictaccessfromotherpartsoftheprogram. Let'sadddifferentmemberstotheStudentclass. Field Aclasscanhaveoneormorefields.Itisaclass-levelvariablethatholdsavalue.Generally,fieldmembersshouldhaveaprivateaccessmodifierusedwithproperty. Example:Field classStudent { publicintid; } Property Apropertyencapsulatesaprivatefieldusingsetterandgettertoassignandretrieveunderlyingfieldvalue. Example:Property classStudent { privateintid; publicintStudentId { get{returnid;} set{id=value;} } } Intheaboveexample,theidisaprivatefieldthatcannotbeaccesseddirectly.ItwillonlybeaccessedusingtheStudentIdproperty. Theget{}returnsthevalueoftheunderlyingfieldandset{}assignsthevaluetotheunderlyingfieldid. Youcanalsoapplysomeadditionallogicingetandset,asinthebelowexample. Example:PropertyinC# privateintid; publicintStudentId { get{returnid;} set{ if(value>0) id=value; } } Auto-implementedProperty FromC#3.0onwards,propertydeclarationhasbeenmadeeasyifyoudon'twanttoapplysomelogicingetterorsetter.Usingauto-implementedproperty,youdon'tneedtodeclareanunderlyingprivatefield. C#compilerwillautomaticallycreateitinILcode. Example:Auto-implementedProperty classStudent { publicstringFirstName{get;set;} publicstringLastName{get;set;} } Intheaboveexample,backingprivatefieldfortheFirstNameandLastNamewillbecreatedinternallybythecompiler.Thisspeedupthedevelopmenttimeandcodereadability. Method Amethodcancontainoneormorestatementstobeexecutedasasingleunit.Amethodmayormaynotreturnavalue.Amethodcanhaveoneormoreinputparameters. Syntax [access-modifier]return-typeMethodName(typeparameterName1,typeparameterName2,...) { } ThefollowingdefinestheSummethodthatreturnsthesumoftwonumbers. Example:C#Method publicintSum(intnum1,intnum2) { vartotal=num1+num2; returntotal; } Thefollowingmethoddoesn'treturnanythinganddoesn'thaveanyparameters.Thereturntypeisvoid. Example:C#Method publicvoidGreet() { Console.Write("HelloWorld!"); } ThefollowingdefinestheGetFullName()methodintheStudentclass. Example:Method classStudent { publicstringFirstName{get;set;} publicstringLastName{get;set;} publicstringGetFullName() { returnFirstName+""+LastName; } } Constructor Aconstructorisaspecialtypeofmethodwhichwillbecalledautomaticallywhenyoucreateaninstanceofaclass. Aconstructorisdefinedbyusinganaccessmodifierandclassname(){}. Example:Constructor classStudent { publicStudent() { //constructor } } Aconstructornamemustbethesameasaclassname. Aconstructorcanbepublic,private,orprotected. Theconstructorcannotreturnanyvaluesocannothaveareturntype. Aclasscanhavemultipleconstructorswithdifferentparametersbutcanonlyhaveoneparameterlessconstructor. Ifnoconstructorisdefined,theC#compilerwouldcreateitinternally. ObjectsofaClass Youcancreateoneormoreobjectsofaclass.Eachobjectcanhavedifferentvaluesofpropertiesandfieldbutmethodsandeventsbehavesthesame. InC#,anobjectofaclasscanbecreatedusingthenewkeywordandassignthatobjecttoavariableofaclasstype. Forexample,thefollowingcreatesanobjectoftheStudentclassandassignittoavariableoftheStudenttype. Example:CreateanObjectofaClass Studentmystudent=newStudent(); Youcannowaccesspublicmembersofaclassusingtheobject.MemberNamenotation. Example:AccessMembersofaClass Studentmystudent=newStudent(); mystudent.FirstName="Steve"; mystudent.LastName="Jobs"; mystudent.GetFullName(); Youcancreatemultipleobjectsofaclasswithdifferentvaluesofpropertiesandfields. Example:CreateMultipleObjectsofaClass Studentmystudent1=newStudent(); mystudent1.FirstName="Steve"; mystudent1.LastName="Jobs"; Studentmystudent2=newStudent(); mystudent2.FirstName="Bill"; mystudent2.LastName="Gates"; C#Questions&Answers StartC#SkillTest RelatedArticles ForeachLoopinC# DesignPrinciplevsDesignPattern DifferencebetweenArrayandArrayList DifferencebetweenHashtableandDictionary HowtowritefileusingStreamWriterinC#? HowtosortthegenericSortedListinthedescendingorder? 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