Chapter 2 Object Orientation. Software Architecture Object Orientation 1

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1 Chapter 2 Object Orientation 1

2 Process Phase Affected by This Chapter Requirements Analysis Framework Design Architecture Detailed Design Key: = less so Implementation 2

3 Before Object Orientation Real world concepts Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Software Design Entities 3

4 How Do We Express Ourselves? "Customers Montague and Susan entered the Ajax bank and were served by teller Andy... " AJAX BANK 4

5 How We Express Ourselves CLASSES "Customers Montague and Susan entered the Ajax bank and were served by teller Andy... " OBJECTS Note that Java code convention reverses this capitalization. 5

6 Object Orientation Real world concepts Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Skljkvjkvjfkavjafkk saovjsdvjfvkfjvkfjk Direct correspondence Customer getfirstname() Graphics reproduced with permission from Corel. Transaction execute() Software design entities Account getdetails() 6

7 Key Concept: à Benefits of OO ß Object orientation provides a direct mapping between concepts and code. 7

8 Real world Class Introduction Class in Design (UML notation) Class in Source code (Java) AjaxCustomer class AjaxCustomer {.... } Mental concept PermissionToPay class PermissionToPay {.... } 8

9 The Members of a Class Objects of Auto Class model Non-static variable: One version for every object alicebrownbmw:auto Auto public int vehicleid protected int mileage private myprivatevariable static int numautosmade Static variable: One version only mileage numautosmade Subclasses have these members too Toyota mytoyota:toyota 2105 mileage jaynescar:auto mileage 9

10 Attribute Types (Shlaer & Mellor) Naming: fixed for each object distinguishes individuals Descriptive: varies through life of object Referential: ties instance of one class to instance(s) of another Auto vehicleid mileage owner == aggregation 10

11 Key Concept: à Classes and Objects ß A class expresses a concept such as HondaCivic. An object is an instance of a class such as the Honda Civic with vehicle ID 89R783HJD

12 class Customer {... String getname() { } int computebalance() { }... Class Customer } class AjaxWebsiteGenerator {... void makeprofile( Customer c ) { String name = c.getname() }... Client of Customer } The Clients of a Class class AjaxAssets {... int computeassets() {... Customer c = customers[ i ]; assets += c.computebalance();... }... Client of Customer } 12

13 Aspects of OO Useful for Application Development q Class Introduction (section 2.2.1) basic motive of Object Orientation identifying parts that corresponds to the real world q Instantiation (section 2.2.2) creating instances of encapsulated concepts q Inheritance (section 2.3.1) capturing the way concepts occur in hierarchy q Polymorphism (section 2.3.2) capturing use of single action word to represent different things, depending on context 13

14 Requirements For Creation Example 1. Summary: Produces text for various types of customers. Page 1 of 4 2. Detailed requirements 2.1 The application displays choices to the console, as shown in figure xx. 2.2 For customers delinquent more than 90 days, the e- mail message generated is the statement shown in figure xx. 14

15 Typical Interaction for Creation Example Page 2 of 4 15

16 Requirements For Creation Example 2.3 All non-delinquent customers receive a tailored messages as follows Mountain customers: This month we have a special on West Face tents. Only $ lots more output specialized to mountaineering customers Regular customers: All items are marked down 20% for this month only.... lots more output for regular customers... Page 3 of 4 16

17 Requirements For Creation Example 2.4 The is to be displayed on the console. Page 4 of 4 3. Future enhancements We anticipate that the text is likely to change frequently, and that new kinds of customers are likely to be specified, each with its own new set of requirements. 17

18 Disadvantages of Branching Code for each case not cohesive ( cohesive : forms a comprehensible unity) All types of customers coded together in single class Expensive to add new functionality bloat switch or if - then code remove functionality hunt for all parts that must be removed change functionality hunt for all parts that must be changed 18

19 Aspects of the Customer Design Needing Improvement We need to visualize the design Code not an effective way to understand design The design s maintainability still has flaws As the application grows, specialized class(es) will be required to interact with the user 19

20 Key Concept: à Polymorphism ß The use of several versions of a method, one in each derived class. This enables objectofbaseclass.themethod() to be interpreted variously at runtime, depending on what derived class objectofbaseclass belongs to. 20

21 What s Needed to Specify Functionality Name of the function Example: add Argument types(if any) Example: First parameter: integer Second parameter: float Return type Example: double, reference type, void Exceptions (if any) Example: IOException More(?) Are parameters inputs and/or outputs? Describe what the function does (natural language) 21

22 The Need For Interfaces: Simplify class Draw { int setcolor( String ) { } Pen getstandardpen() { } int getlogostyle() { } void setcolor( int ) { } void drawlogo( int, int ) { } void speeduppen( int ) { } } 22

23 Interface Example: a Draw Class Functions dealing with the pen used Pen getstandardpen() void speeduppen( int )... Functions dealing with the colors available void setcolor( int ) int setcolor( String )... Functions covering the drawing of the company s logo void drawlogo( int, int ) int getlogostyle() } Pen interface } } Color interface Logo interface 23

24 Key Concept: à Interfaces ß An interface is a set of function prototypes (each with name, parameter types, return type, exception type). 24

25 Issues to be Addressed How do we visualize a set of classes? How can classes relate to each other? How should classes relate to each other? How can we describe functionality occurring among several classes? How do we describe the manner in which objects respond to events occurring on them? Are there patterns of class usage that recur? So we can existing design parts 25

26 Typical Interaction for Auto Description Exercise 26

27 Summary of This Chapter A Class represents a concept Example: House An Object is an instance of a class Example: 23 Main Street, Springfield Classes can relate in several ways: Mainly A Client of a class refers to that class in one of its methods Inheritance: kind of relationship Aggregation: has a relationship, explained in chapter xx Polymorphism means action depends on context Executing anobject.amethod() actually executes the version of amethod() in the subclass that anobject belongs to 27

Object-Oriented Modeling Using UML. CS151 Chris Pollett Aug. 29, 2005.

Object-Oriented Modeling Using UML CS151 Chris Pollett Aug. 29, 2005. Outline Objects and Classes Modeling Relationships and Structures Some Terms and Concepts Objects and classes are fundamental to OO