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1Design and UMLClass DiagramsWEEK 71Big questionsWhat is UML?What is a UML class diagram?? What kind of information goes into it?? How do I create it?? When should I create it?22Design phasedesign: specifying the structure of how a softwaresystem will be written and function, withoutactually writing the complete implementationa transition from “what” the system must do, to“how” the system will do it? What classes will we need to implement a system thatmeets our requirements?? What fields and methods will each class have?? How will the classes interact with each other?3How do we design classes?class identification from project spec / requirements? nouns are potential classes, objects, fields? verbs are potential methods or responsibilities of a classCRC card exercises? write down classes’ names on index cards? next to each class, list the following:? responsibilities: problems to be solved; short verb phrases? collaborators: other classes that are sent messages by this class (asymmetric)UML diagrams? class diagrams (today)? sequence diagrams? …43Introduction to UMLUML: pictures of an OO system? programming languages are not abstract enough for OO design? UML is an open standard; lots of companies use itWhat is legal UML?? a descriptive language: rigid formal syntax (like programming)? a prescriptive language: shaped by usage and convention? it’s okay to omit things from UML diagrams if they aren’t needed byteam/supervisor/instructor5Uses for UMLas a sketch: to communicate aspects of system? forward design: doing UML before coding? backward design: doing UML after coding as documentation? often done on whiteboard or paper? used to get rough selective ideasas a blueprint: a complete design to be implemented? sometimes done with CASE (Computer-Aided Software Engineering) toolsas a programming language: with the right tools, code can be autogenerated and executed from UML? only good if this is faster than coding in a “real” language64UML class diagramsWhat is a UML class diagram?What are some things that are not represented in a UML class diagram?7? details of how the classes interact with each other? algorithmic details; how a particular behavior isimplemented? UML class diagram: a picture of the classes in anOO system, their fields and methods, andconnections between the classes that interact orinherit from each otherDiagram of one classclass name in top of box? write on top of interfaces’ names? use italics for an abstract class nameattributes (optional)? should include all fields of the objectoperations / methods (optional)? may omit trivial (get/set) methods? but don’t omit any methods from an interface!? should not include inherited methods85Class attributesattributes (fields, instance variables)? visibility name : type [count] = default_value? visibility: + public# protected– private~ package (default)/ derived? underline static attributes? derived attribute: not stored, but canbe computed from other attribute values? attribute example:– balance : double = 0.009Class operations / methodsoperatio

ns / methods? visibility name (parameters) : return_type? visibility: + public# protected– private~ package (default)? underline static methods? parameter types listed as (name: type)? omit return_type on constructors andwhen return type is void? method example:+ distance(p1: Point, p2: Point): double106Commentsrepresented as a folded note, attached to the appropriateclass/method/etc by a dashed line11Relationships btwn. classesgeneralization: an inheritance relationship? inheritance between classes? interface implementationassociation: a usage relationship? dependency? aggregation? composition127Generalization relationshipsgeneralization (inheritance) relationships? hierarchies drawn top-down with arrows pointingupward to parent? line/arrow styles differ, based on whether parent isa(n):? class:solid line, black arrow? abstract class:solid line, white arrow? interface:dashed line, white arrow? we often don’t draw trivial / obvious generalizationrelationships, such as drawing the Object class as aparent13Associational relationshipsassociational (usage) relationships1. multiplicity (how many are used)? * ? 0, 1, or more? 1 ? 1 exactly? 2..4 ? between 2 and 4, inclusive? 3..* ? 3 or more2. name (what relationship the objects have)3. navigability (direction)148Multiplicity of associations15? one-to-one? each student must carry exactly one ID card? one-to-many? one rectangle list can contain many rectanglesAssociation typesaggregation: “is part of”? symbolized by a clear white diamondcomposition: “is entirely made of”? stronger version of aggregation? the parts live and die with the whole? symbolized by a black diamonddependency: “uses temporarily”? symbolized by dotted line? often is an implementationdetail, not an intrinsic part ofthat object’s state16 1 1Engine Car aggregation LotteryTicket Randomdependency Page* Book composition19Class diagram example 117Class diagram example 218 DVD MovieVHS MovieVideo GameComposition Rental Item Rental InvoiceCheckout Screen0..1 1..*1 Customer1 SimpleAssociationClassAbstractClassSimpleAggregationGeneralizationMultiplicity10Class diagram example 319 StudentBodyStudent+ main (args : String[])+ toString() : String1 100– firstName : String– lastName : String– homeAddress : Address– schoolAddress : Address + toString() : String– streetAddress : String– city : String– state : String– zipCode : longAddress Tools for creating UML diags.Violet (free)? http://horstmann.com/violet/Rational Rose? http://www.rational.com/Visual Paradigm UML Suite (trial)? http://www.visual-paradigm.com/? (nearly) direct download link:http://www.visual-paradigm.com/vp/download.jsp?product=vpuml&edition=ce(there are many others, but most are commercial)2011Class design exerciseConsider the case study in the assignment brief on your Moodle;? What classes are in this system? What are their responsibilities? Whichclasses collaborate?? Draw a class diagram for this system. Include relationships between classes(generalization and associational).21