Chapter 9Inheritance RevisitedSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Java Access ModifiersSlide 10Is-a and Has-a RelationshipsIs-a RelationshipSlide 13Has-a RelationshipsSlide 15Dynamic Binding and Abstract ClassesSlide 17Slide 18Slide 19Slide 20PowerPoint Presentation© 2006 Pearson Addison-Wesley. All rights reserved 9 A-1Chapter 9Advanced Java TopicsCS102 Sections 51 and 52Marc Smith and Jim Ten EyckSpring 2007© 2006 Pearson Addison-Wesley. All rights reserved 9 A-2Inheritance Revisited•Inheritance–Allows a class to derive the behavior and structure of an existing class© 2006 Pearson Addison-Wesley. All rights reserved 9 A-3Inheritance RevisitedFigure 9-1Figure 9-1Inheritance: Relationships among timepieces© 2006 Pearson Addison-Wesley. All rights reserved 9 A-4Inheritance Revisited•Superclass or base class–A class from which another class is derived•Subclass, derived class, or descendant class–A class that inherits the members of another class•Benefits of inheritance–It enables the reuse of existing classes–It reduces the effort necessary to add features to an existing object© 2006 Pearson Addison-Wesley. All rights reserved 9 A-5Inheritance Revisited•A subclass –Can add new members to those it inherits–Can override an inherited method of its superclass•A method in a subclass overrides a method in the superclass if the two methods have the same declarations© 2006 Pearson Addison-Wesley. All rights reserved 9 A-6Inheritance RevisitedFigure 9-2Figure 9-2The subclass Ball inherits members of the superclass Sphere and overrides and adds methods© 2006 Pearson Addison-Wesley. All rights reserved 9 A-7Inheritance Revisited•A subclass inherits private members from the superclass, but cannot access them directly•Methods of a subclass can call the superclass’s public methods•Clients of a subclass can invoke the superclass’s public methods•An overridden method–Instances of the subclass will use the new method–Instances of the superclass will use the original method© 2006 Pearson Addison-Wesley. All rights reserved 9 A-8Inheritance RevisitedFigure 9-3Figure 9-3An object invokes the correct version of a method© 2006 Pearson Addison-Wesley. All rights reserved 9 A-9Java Access ModifiersFigure 9-4Figure 9-4Access to public, protected, package access, and private members of a class by a client and a subclass© 2006 Pearson Addison-Wesley. All rights reserved 9 A-10Java Access Modifiers•Membership categories of a class–Public members can be used by anyone–Members declared without an access modifier (the default) are available to•Methods of the class•Methods of other classes in the same package–Private members can be used only by methods of the class–Protected members can be used only by•Methods of the class•Methods of other classes in the same package•Methods of the subclass© 2006 Pearson Addison-Wesley. All rights reserved 9 A-11Is-a and Has-a Relationships•Two basic kinds of relationships–Is-a relationship–Has-a relationship© 2006 Pearson Addison-Wesley. All rights reserved 9 A-12Is-a Relationship•Inheritance should imply an is-a relationship between the superclass and the subclass•Example:–If the class Ball is derived from the class Sphere•A ball is a sphereFigure 9-5Figure 9-5A ball “is a” sphere© 2006 Pearson Addison-Wesley. All rights reserved 9 A-13Is-a Relationship•Object type compatibility–An instance of a subclass can be used instead of an instance of the superclass, but not the other way around© 2006 Pearson Addison-Wesley. All rights reserved 9 A-14Has-a RelationshipsFigure 9-6Figure 9-6A pen “has a” or “contains a” ball© 2006 Pearson Addison-Wesley. All rights reserved 9 A-15Has-a Relationships•Has-a relationship–Also called containment–Cannot be implemented using inheritance•Example: To implement the has-a relationship between a pen and a ball–Define a data field point – whose type is Ball – within the class Pen© 2006 Pearson Addison-Wesley. All rights reserved 9 A-16Dynamic Binding and Abstract Classes•A polymorphic method–A method that has multiple meanings–Created when a subclass overrides a method of the superclass•Late binding or dynamic binding–The appropriate version of a polymorphic method is decided at execution time© 2006 Pearson Addison-Wesley. All rights reserved 9 A-17Dynamic Binding and Abstract ClassesFigure 9-7aFigure 9-7aarea is overridden: a) mySphere.DisplayStatistics( ) calls area in Sphere© 2006 Pearson Addison-Wesley. All rights reserved 9 A-18Dynamic Binding and Abstract ClassesFigure 9-7bFigure 9-7barea is overridden: b) myBall.displayStatistics( ) calls area in Ball© 2006 Pearson Addison-Wesley. All rights reserved 9 A-19Dynamic Binding and Abstract Classes•Controlling whether a subclass can override a superclass method–Field modifier final•Prevents a method from being overridden by a subclass–Field modifier abstract•Requires the subclass to override the method•Early binding or static binding–The appropriate version of a method is decided at compilation time–Used by methods that are final or static© 2006 Pearson Addison-Wesley. All rights reserved 9 A-20Dynamic Binding and Abstract Classes•Overloading methods–To overload a method is to define another method with the same name but with a different set of parameters–The arguments in each version of an overloaded method determine which version of the method will be used© 2006 Pearson Addison-Wesley. All rights reserved 9 A-21Please open file carrano _ppt09_B.ppt to continue viewing chapter