Object Oriented Programming: InheritanceWhat You Will LearnIntroductionSlide 4Base Classes & Derived ClassesSuperclass and SubclassSlide 7Design Tipprotected MembersComments on Private vs. ProtectedRelationship between Superclasses and SubclassesCreating and Using a CommissionEmployee ClassSlide 13Creating a BasePlusCommissionEmployee Class without Using InheritanceCreating a CommissionEmployee-BasePlusCommiionEmployee Inheritance HierarchyUsing protected Instance VariablesUsing protected Instance Variables AdvantagesUsing protected Instance Variables DisadvantagesReexamine HierarchyInstantiating Subclass ObjectSlide 21Software Engineering with InheritanceObject Oriented Object Oriented Programming: InheritanceProgramming: InheritanceChapter 9Chapter 922What You Will LearnWhat You Will LearnSoftware reusabilitySoftware reusability(Recycling)(Recycling)Inheriting data members and methods from Inheriting data members and methods from previously defined classespreviously defined classes33IntroductionIntroductionSoftware ReusabilitySoftware Reusabilitysaves time in program developmentsaves time in program developmentencourages use of proven, debugged codeencourages use of proven, debugged codereduces problemsreduces problemsWrite programs in general fashionWrite programs in general fashionEnables software designers to deal with Enables software designers to deal with complexity of modern softwarecomplexity of modern software44IntroductionIntroductionWhen creating a new class …When creating a new class …designate that class to inherit data members, designate that class to inherit data members, functions of previously defined functions of previously defined superclasssuperclassresult is a result is a subclasssubclassSubclass adds new data members and Subclass adds new data members and functionsfunctionsReplace and refine existing membersReplace and refine existing members55Base Classes & Derived Base Classes & Derived ClassesClassesSuperclass is more generalSuperclass is more generalstudent, shape, loanstudent, shape, loanSubclass is more specificSubclass is more specificgrad student, undergradgrad student, undergradcircle, triangle, rectanglecircle, triangle, rectanglecarloan, home improvement, mortgagecarloan, home improvement, mortgageSome languages talk ofSome languages talk ofBase class (Superclass)Base class (Superclass)Derived class (Subclass)Derived class (Subclass)66Superclass and SubclassSuperclass and SubclassInheritance produces tree like structuresInheritance produces tree like structures77Superclass and SubclassSuperclass and SubclassInheritance produces tree like structuresInheritance produces tree like structures88Design TipDesign TipImportant link between subclass and Important link between subclass and superclasssuperclassThe “IS-A” relationshipThe “IS-A” relationshipExamplesExamplesA checking account IS-A banking accountA checking account IS-A banking accountA savings account IS NOT a checking accountA savings account IS NOT a checking accountIf there is no IS-A relationship, do not If there is no IS-A relationship, do not use inheritanceuse inheritanceSun comments on the concept of inheritanceSun comments on the concept of inheritance99protectedprotected Members Membersprotectedprotected access accessIntermediate level of protection between Intermediate level of protection between publicpublic and and privateprivateprotectedprotected members accessible by members accessible bysuperclass memberssuperclass memberssubclass memberssubclass membersClass members in the same packageClass members in the same packageSubclass access to superclass memberSubclass access to superclass memberKeyword Keyword supersuper and a dot (.) and a dot (.)1010Comments on Private vs. ProtectedComments on Private vs. ProtectedUse Use protectedprotected when when Superclass should provide a service only to its Superclass should provide a service only to its subclassessubclassesShould not provide service to other clientsShould not provide service to other clientsUse Use privateprivate so that so thatSuperclass implementation can change without affecting Superclass implementation can change without affecting subclass implementationssubclass implementationsAuthor advocates avoiding Author advocates avoiding protectedprotectedInstead provide set and get methods to access Instead provide set and get methods to access privateprivate data items (see data items (see Figures 9.12Figures 9.12, , 9.139.13 in text) in text)1111Relationship between Superclasses Relationship between Superclasses and Subclassesand SubclassesSuperclass and subclass relationshipSuperclass and subclass relationshipExample: Example: CommissionEmployee/CommissionEmployee/BasePlusCommissionEmployeeBasePlusCommissionEmployee inheritance inheritance hierarchyhierarchyCommissionEmployeeCommissionEmployeeFirst name, last name, SSN, commission rate, gross sale First name, last name, SSN, commission rate, gross sale amountamountBasePlusCommissionEmployeeBasePlusCommissionEmployeeFirst name, last name, SSN, commission rate, gross sale First name, last name, SSN, commission rate, gross sale amountamountBase salaryBase salary1212Creating and Using a Creating and Using a CommissionEmployeeCommissionEmployee Class ClassClass Class CommissionEmployeeCommissionEmployeeExtends class Extends class ObjectObjectKeyword Keyword extendsextendsEvery class in Java extends an existing classEvery class in Java extends an existing classExcept Except ObjectObjectEvery class inherits Every class inherits ObjectObject’s methods’s methodsNew class implicitly extends ObjectNew class implicitly extends ObjectIf it does not extend another classIf it does not extend another class1313Creating and Using a Creating and Using a CommissionEmployeeCommissionEmployee Class ClassClass Class CommissionEmployeeCommissionEmployeeExtends class Extends class ObjectObjectKeyword Keyword extendsextendsEvery class in Java extends an existing classEvery class in Java extends an existing classExcept Except ObjectObjectEvery class inherits Every class inherits ObjectObject’s methods’s methodsNew class implicitly extends ObjectNew class implicitly extends ObjectIf it does not extend another classIf it does not extend another classView class View class