1 CS 501 Spring 2002 CS 501: Software Engineering Lecture 16 Object Oriented Design I

2 CS 501 Spring 2002 Administration

3 CS 501 Spring 2002 The Waterfall Model Requirements Analysis System design Unit & Integration Testing System Testing Operation & Maintenance Program design Coding Acceptance Testing Requirements Design Implementation

4 CS 501 Spring 2002 Program Design The task of program design is to represent the software system functions in a form that can be transformed into one or more executable programs. Given a system architecture, the program design specifies: computers and networks programs, components, packages, classes and class hierarchies interfaces, protocols security mechanisms, operational procedures

5 CS 501 Spring 2002 The Importance of Modeling A model is a simplification of reality. We build models so that we can better understand the system we are developing. We build models of complex system because we cannot comprehend such a system in its entirety. Models can be informal or formal. The more complex the project the more valuable a formal model becomes. BRJ

6 CS 501 Spring 2002 Principles of Modeling The choice of what models to create has a profound influence on how a problem is attacked and how a solution is shaped. Every model can be expressed at different levels of precision. The best models are connected to reality. No single model is sufficient. Every nontrivial system is best approached through a small set of nearly independent models. BRJ

7 CS 501 Spring 2002 The Unified Modeling Language UML is a standard language for modeling software systems Serves as a bridge between the requirements specification and the implementation. Provides a means to specify and document the design of a software system. Is process and programming language independent. Is particularly suited to object-oriented program development.

8 CS 501 Spring 2002 Useful Texts Grady Booch, James Rumbaugh, Ivar Jacobson, The Unified Modeling Language. Addison-Wesley Grady Booch, Object-Oriented Analysis and Design with Applications, second edition. Benjamin/Cummings Rob Pooley, Perdita Stevens, Using UML Software Engineering with Objects and Components. Addison-Wesley 1999.

9 CS 501 Spring 2002 Rational Rose Rational Rose is a system for creating and managing UML diagrams. It is available on all Computer Science Department computers. See: for installation instructions.

10 CS 501 Spring 2002 Notation: Classes Window origin size open() close() move() display() name attributes operations A class is a description of a set of objects that share the same attributes, operations, relationships and semantics.

11 CS 501 Spring 2002 The HelloWorld Example HelloWorld paint() class name operations

12 CS 501 Spring 2002 Notation: Grouping and Annotation A package is a general-purpose mechanism for organizing elements into groups. Business rules return copy of self A note is a symbol for rendering constraints and comments attached to an element or a collection of elements.

13 CS 501 Spring 2002 Abstraction for HelloWorld HelloWorld paint() g.drawString ("HelloWorld", 0, 10)" class name operations annotation

14 CS 501 Spring 2002 Class Diagram Applet HelloWorld paint() Graphics generalization dependency Note that the Applet and Graphics classes are shown elided.

15 CS 501 Spring 2002 Class Inheritance Diagram Object Component Container Panel Applet HelloWorld ImageObserver interface

16 CS 501 Spring 2002 Packaging Classes applet awt lang HelloWorld java Graphics package

17 CS 501 Spring 2002 Notation for Classes and Objects Classes Objects AnyClass attribute1 attribute2 operation1() operation2() AnyClass or anObject:AnyClass :AnyClass anObject The names of objects are underlined. or

18 CS 501 Spring 2002 The "Hello, World" Implementation import java.awt.Graphics; class HelloWorld extends java.applet.Applet { public void paint (Graphics g) { g.drawString ("Hello, World!", 10, 10); } Example from: BJR

19 CS 501 Spring 2002 Notation: Interface An interface is a collection of operations that specify a service of a class or component, i.e., the externally visible behavior of that element. ISpelling

20 CS 501 Spring 2002 Notation: Collaboration & Use Case Place order A use case is a description of a set of sequence of actions that a system performs that yields an observable result. Chain of responsibility A collaboration defines an interaction, i.e., a society of roles and other elements that work together to provide some cooperative behavior.

21 CS 501 Spring 2002 Notation: Active Class EventManager eventlist suspend() flush() An active class is a class whose objects own one or more processes or threads and therefore can initiate control activity.

22 CS 501 Spring 2002 Notation: Component & Node orderform.java A component is a physical and replaceable part of a system that conforms to and provides the realization of a set of interfaces. Server A node is a physical element that exists at run time and represents a computational resource.

23 CS 501 Spring 2002 Notation: Behavioral Things: Messages & States display An interaction is a behavior that comprises a set of messages exchanged among a set of objects within a particular context to accomplish a specific purpose. Waiting A state machine is a behavior that specifies the sequence of states an object or an interaction goes through during its lifetime in response to events.

24 CS 501 Spring 2002 Notation: Relationships A dependency is a semantic relationship between two things in which a change to one may effect the semantics of the other * employer employee An association is a structural relationship that describes a set of links, a link being a connection among objects.

25 CS 501 Spring 2002 Relationships Parking Parking Space location is_available()

26 CS 501 Spring 2002 Notation: Relationships (continued) A generalization is a specialization/generalization relationship is which objects of the specialized element (child) are substitutable for objects of the generalized element (parent). childparent A realization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out.

27 CS 501 Spring 2002 Diagrams in UML A diagram is the graphical representation of a set of elements, usually rendered as a connected graph of vertices (things) and arcs (relationships). Class diagram shows a set of classes, interfaces, and collaborations with their relationships. Object diagram shows a set of objects and their relationships. Use case diagram shows a set of use cases and actors (a special kind of class) and their relationships.

28 CS 501 Spring 2002 Diagrams in UML (continued) Interaction diagram shows an interaction, consisting of a set of objects and the relationships, including the messages that may be dispatched among them. => A sequence diagram emphasizes the time ordering. => A collaboration diagram emphasizes the structural organization of the objects that send and receive messages.

29 CS 501 Spring 2002 Example: A Sequence Diagram BookBorrower libMem: LibraryMember theCopy:Copy theBook:Book borrow(theCopy) okToBorrow borrow

30 CS 501 Spring 2002 Diagrams in UML (continued) Statechart diagram shows a state machine consisting of states, transitions, events, and activities. Activity diagram is a statechart diagram that shows the flow from activity to activity within a system. Component diagram shows the organization and dependencies among a set of components. Deployment diagram shows the configuration of processing nodes and the components that live on them.