Chapter 8 Additional Inheritance Concepts and Techniques

1. Chapter 8Additional Inheritance Concepts and Techniques Chapter 8 - Additional Inheritance Concepts and Techniques

2. Chapter 8 Topics • Require a subclass to override a superclass method by including an abstract method in the superclass • Creating a Java interface and using an interface to require a class to implement methods • Creating and using custom exceptions that provide detailed information about an error by extending the Exception class • How all Java classes implicitly extend the Object class Chapter 8 - Additional Inheritance Concepts and Techniques

3. Introducing the Initial Lease Class • Bradshaw Marina Case Study • Includes three generalization/specialization hierarchies that require inheritance • Boat (Sail, Power), Slip (Covered), Lease (Annual, Daily) • Lease hierarchy • Introduces additional inheritance concepts • Introduces problem domain classes that contain attributes that hold references to other objects Chapter 8 - Additional Inheritance Concepts and Techniques

4. Chapter 8 - Additional Inheritance Concepts and Techniques

5. Adding an Abstract Method to Lease • Abstract Method (Figure 8-5) • Method without any statements • Requires that a subclass include or implement the method • If a class has an abstract method: • The class must also be abstract • Keyword • abstract Chapter 8 - Additional Inheritance Concepts and Techniques

6. Implementing the AnnualLease Subclass • AnnualLease Class (Figure 8-6) • Extends Lease class • Adds attributes • Constructors and methods more complex • Imports java.util package for Date and Calendar classes • Both subclass and superclass must do this Chapter 8 - Additional Inheritance Concepts and Techniques

7. Implementing the DailyLease Subclass • DailyLease Class (Figure 8-7) • Extends Lease class • Adds attribute • Constructors and methods more complex • Imports java.util package for Date and Calendar classes • Both subclass and superclass must do this Chapter 8 - Additional Inheritance Concepts and Techniques

8. Testing the AnnualLease and DailyLease Classes • TesterTwo Class (Figure 8-8) • Tests AnnualLease and DailyLease classes • Instantiates objects of both classes • Instantiates date objects • Retrieves information about each lease object Chapter 8 - Additional Inheritance Concepts and Techniques

9. Understanding and Using Java Interfaces • Two methods to require that class override a method: • Add an abstract method to the superclass that the class derives from • Define an interface that the class implements • Interface • Java component that defines abstract methods and constants that must be included by implementing classes Chapter 8 - Additional Inheritance Concepts and Techniques

10. Understanding and Using Java Interfaces • Concept • Knowing how to use something means knowing how to interface with it • The methods an instance can respond to can be defined as the interface to the instance • To assure instance has a defined set of methods: • Define an interface and have class implement it Chapter 8 - Additional Inheritance Concepts and Techniques

11. Understanding and Using Java Interfaces • Component-based development • System components interact using well-defined interface built from a variety of technologies • If interface is known  can be used in system • Do not need to know technology used or internal structure of component Chapter 8 - Additional Inheritance Concepts and Techniques

12. Understanding and Using Java Interfaces • Multiple inheritance • Ability to “inherit” from more than one class • Java allows only single inheritance • Using extends keyword • Interfaces allow Java an alternative mechanism to emulate the concept of multiple inheritance Chapter 8 - Additional Inheritance Concepts and Techniques

13. Understanding and Using Java Interfaces • Creating a Java Interface • Created much the same way as a class • Header • Use interface keyword: • public interface LeaseInterface • Abstract methods • Implement using implements keyword: • public class AnnualLease extends Lease implements LeaseInterface Chapter 8 - Additional Inheritance Concepts and Techniques

14. Chapter 8 - Additional Inheritance Concepts and Techniques

15. Understanding and Using Java Interfaces • Implementing More Than One Interface • Java classes can implement more than one interface • Use comma separated list: • Interfaces can include static final variables (constants) – Figure 8-11 • All classes that implement the interface have the constants available • DailyLease in Figure 8-12 Chapter 8 - Additional Inheritance Concepts and Techniques

16. Understanding and Using Java Interfaces • Testing the Complete Interface Example • TesterThree class (Figure 8-13) • Tests: • AnnualLease with one interface • DailyLease with two interfaces Chapter 8 - Additional Inheritance Concepts and Techniques

17. Using Custom Exceptions • Custom exception • Exception written specifically for a particular application • Extends a built-in class • Any class that is not declared final can be extended Chapter 8 - Additional Inheritance Concepts and Techniques

18. Using Custom Exceptions • Defining the LeasePaymentException (Fig. 8-15) • Extend custom exception from Exception class • Add appropriate components: • Attributes • Constructors • Methods • Sequence diagram • Shows interaction between the LeasePaymentException class and the AnnualLease class Chapter 8 - Additional Inheritance Concepts and Techniques

19. Chapter 8 - Additional Inheritance Concepts and Techniques

20. Using Custom Exceptions • Throwing a Custom Exception • AnnualLease class (Figure 8-17) • Uses LeasePaymentException class • Use throws keyword in method declaration • Use throw keyword in method body Chapter 8 - Additional Inheritance Concepts and Techniques

21. Using Custom Exceptions • Testing the LeasePaymentException • TesterFour class • Tests: • Revised AnnualLease class • LeasePaymentException class • Sequence diagram • Shows interactions for TesterFour class Chapter 8 - Additional Inheritance Concepts and Techniques

22. Chapter 8 - Additional Inheritance Concepts and Techniques

23. Chapter 8 - Additional Inheritance Concepts and Techniques

24. Chapter 8 - Additional Inheritance Concepts and Techniques

25. Using Custom Exceptions • Handling Payments as a Batch • Batch processing • Takes a collection of transactions and processes them one after the other • If successful: • Success message is displayed • If unsuccessful: • Exception message is displayed (but processing continues) • Useful in testing validation and exceptions Chapter 8 - Additional Inheritance Concepts and Techniques

26. Chapter 8 - Additional Inheritance Concepts and Techniques

27. Chapter 8 - Additional Inheritance Concepts and Techniques

28. Chapter 8 - Additional Inheritance Concepts and Techniques

29. Understanding the Object Class and Inheritance • All Java classes extend from Object class • Object class • Defines basic functionality that any other class of objects need in Java • All built-in class hierarchies have Object as common ancestor • All custom problem domain classes extend Object as well (implicitly) Chapter 8 - Additional Inheritance Concepts and Techniques

30. Chapter 8 - Additional Inheritance Concepts and Techniques