lecture6-part1_inheritance

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1、Object‐OrientedProgrammingLecture6Part1:InheritanceDr.LouisTangUnitedInternationalCollegeFall2010Outline•ClassInheritance•Keyword:extend•Overridemethod•Keyword:super•Keyword:final•ObjectClass•toStringandequalsIntroductiontoInheritance•Inheritanceisoneofthemaintechniq

2、uesofobject‐orientedprogramming(OOP)•Usingthistechnique,averygeneralformofaclassisfirstdefinedandcompiled,andthenmorespecializedversionsoftheclassaredefinedbyaddinginstancevariablesandmethods–Thespecializedclassesaresaidtoinheritthemethodsandinstancevariablesofthegen

3、eralclassIntroductiontoInheritance•Inheritanceistheprocessbywhichanewclassiscreatedfromanotherclass–Thenewclassiscalledasubclassorderivedclass–Theoriginalclassiscalledthesuperclassorbaseclass•Asubclassautomaticallyhasalltheinstancevariablesandmethodsthatthesuperclass

4、has,anditcanhaveadditionalmethodsand/orinstancevariablesaswell•Inheritanceisespeciallyadvantageousbecauseitallowscodetobereused,withouthavingtocopyitintothedefinitionsofthesubclassesTestPerson.javaMemoryAnalysisstackheapPersonnameageStudentSchoolDatasegmentInheritanc

5、einUMLPerson#nameSuper#ageClass+getName()+setName()+getAge()+setAge()InheritancerelationshipStudent-schoolSubClass+getSchool()+setSchool()+toString()+equals()Example:DerivedPersonClasses•Creatingasubclassisactuallyquitesimple.Atthebeginningofyourclassdeclaration,uset

6、heextendskeyword,followedbythenameoftheclasstoinheritfrom:classStudentextendsPerson{//newfieldsandmethodsdefiningastudentgohere}•ThisgivesStudentallthesamefieldsandmethodsasPerson,yetallowsitscodetofocusexclusivelyonthefeaturesthatmakeitunique.SubClasses•Whenasubclas

7、sisdefined,itissaidtoinherittheinstancevariablesandmethodsofthesuperclassthatitextends–ClassStudentdefinestheinstancevariablesschoolinitsclassdefinition•JustasitinheritstheinstancevariablesoftheclassPerson,theclassStudentinheritsallofitsmethodsaswell–TheclassStudenti

8、nheritsthemethodssetName,getName,setAge,andgetAgefromtheclassPerson–AnyobjectoftheclassStudentcanuseoneofthesemethods.–Studenthastw