1 / 27

Object Oriented Design and Programming II Chapter 10 Abstract classes and Interfaces

Object Oriented Design and Programming II Chapter 10 Abstract classes and Interfaces. Software Engineering Principle. Minimize change. From concrete classes. To abstract classes To interface Examples: BJ_1_initial_SalCal BJ_2_class_SalCal BJ_3_abstract_SalCal

carson-ramirez
Download Presentation

Object Oriented Design and Programming II Chapter 10 Abstract classes and Interfaces

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Object Oriented Design and Programming II Chapter 10Abstract classes and Interfaces Abstract classes & Interface

  2. Software Engineering Principle Minimize change

  3. From concrete classes To abstract classes To interface Examples: BJ_1_initial_SalCal BJ_2_class_SalCal BJ_3_abstract_SalCal BJ_4_abstract_method_SalCal BJ_5_interface_SalCal

  4. abstract and final Methods • An abstract method in a superclass has no implementation, and it is to be overridden by a method in its subclass. • A final method in a superclass cannot be overridden at its subclass. • Why do I need to bother with abstract methods and final methods? Can I live happily in Java without them? Abstract classes & Interface

  5. Abstract Class • A class that cannot instantiate objects. Message Text Message Voice Message Fax Message Public abstract class Message { } Do I and should I use non-abstract methods in abstract classes? Abstract classes & Interface

  6. Abstract or not-abstract Abstract classes & Interface

  7. Example BJ_abstract_Figure • Problems of Bj_FindArea • BJ_abstract_Figure • An abstract class used as supertype • An object cannot be created from an abstract class • An abstract class can be extended by a subclass Abstract classes & Interface

  8. Example BJ_abstract_Figure2 • An abstract class used as supertype • An object cannot be created from an abstract class • An array of the abstract type is used to contain objects of the concrete subclasses Abstract classes & Interface

  9. Example BJ_GeomObj_Circle9 • Circle9 extends an abstract class GeometricObject • Note the 4 situations in the project: • Circle class has concrete method getArea() • No abstract method getArea(); concrete getArea() in Circle • abstract method getArea(); concrete getArea() in Circle • Instantiate object of abstract class Abstract classes & Interface

  10. Empty vs abstract methods • Method with empty body • protected abstract double getArea(); • Abstract method • protected abstract double getArea(); Abstract classes & Interface

  11. From abstract class To Interface

  12. What is Interface • An interface is a named collection of method definitions and constants ONLY. • An interface defines a protocol of behavior that can be implemented by any class anywhere in the class hierarchy. • An interface defines a set of methods but does not implement them. • A class that implements the interface agrees to implement all the methods defined in the interface, thereby agreeing to certain behaviors. Abstract classes & Interface

  13. Interface and Abstract Classes • An interface cannot implement any methods, whereas an abstract class can. • A class can implement many interfaces but can have only one superclass. • An interface is not part of the class hierarchy. Unrelated classes can implement the same interface. Abstract classes & Interface

  14. Multiple Inheritance Class A Class B Class C Class ABC Class ABC inherits all variables and methods from Class A, Class B, and Class C. Java does NOT support multiple inheritances. However, you can use interface to implement the functionality of multiple inheritance. Abstract classes & Interface

  15. Defining Interfaces Abstract classes & Interface

  16. Interface Declaration public interface StockWatcher{ } public interface Sortable{ } Abstract classes & Interface

  17. Interface Body • The interface body contains method declarations for ALL the methods included in the interface. • A method declaration within an interface is followed by a semicolon (;) because an interface does not provide implementations for the methods declared within it. • All methods declared in an interface are implicitly public and abstract. Abstract classes & Interface

  18. Implement an Interface • An interface defines a protocol of behavior. • A class that implements an interface adheres to the protocol defined by that interface. • To declare a class that implements an interface, include an implements clause in the class declaration. Abstract classes & Interface

  19. Implement Interface (Example) public class StockApplet extends AppletimplementsStockWatcher { ... public void valueChanged(String tickerSymbol, double newValue) { if (tickerSymbol.equals(sunTicker)) { // record newValue for sunTicker... } else if (tickerSymbol.equals(oracleTicker)) { // record newValue for oracleTicker } else if (tickerSymbol.equals(ciscoTicker)) { // record newValue for ciscoTicker } } } Abstract classes & Interface

  20. Code Review • BJ_Interface • Objects inheriting properties of superclass and implementing properties of interface • A class may have only one superclass but may implement multiple interfaces • Using an array of supertype • polymorphism Abstract classes & Interface

  21. Sorting • It is easy to write a sorting method for numbers of a specific type. • bubblesort, shellsort, quicksort, heapsort. • It is not easy to write a method to sort numbers of any primitive type: short, int, long, float, and double. • See Example 9.2 GenericSort.java • It is a challenge to write a method to sort objects • How do you do the above in C? Abstract classes & Interface

  22. Example: Comparable interface • Java.lang.Comparable • See BJ_Max • See BJ_GenericSort • Still relying on Java 1.5 unboxing feature of wrapper objects

  23. Source Code Review and Demo • Exercise 1: Download, run, and study BJ_Sort/SortTest.java • Each class needs to implement the Sortable interface with a compare() method • Exercise 2: Add other sorting methodsBubble, Insertion, Selection • Exercise 3: C:\ProgramFiles\Java\ jdk1.5.0_12\demo\applets\SortDemo • To compare speed

  24. Application Programming Interface (API) • How do I learn to use the packages in the Java platform? • Answer: API • http://java.sun.com/j2se/1.5.0/docs/api/ Abstract classes & Interface

  25. API Studyexample: StringTokenizer • Location of the API( package) • Class definition • Constructor(s) – usually more than one • Methods (you can see public only) • Variables (any public ones) • Interfaces – supply your own methods • Exceptions • Examples Abstract classes & Interface

  26. Clone() newObject = someObject; Only assigns the reference of someObject to newObject. No copy is made newObject = someObject.clone(); Copies someObject to a new memory location See BJ_House

  27. hashCode() hashCode() returns the object’s hash code Hash code is an integer to store the object in a hash set. If you override the equal() method, you should also override the hashCode See BJ_House

More Related