Chapter 16

UML Class Diagrams

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What They Are

• They illustrate classes, interfaces, and their associations. They are used for static object modeling.

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Design Class Diagram

• A class diagram can be used to visualize a domain model. We also need a unique term to clarify when the class diagram is used in a software or design perspective. A common modeling term for this purpose is design class diagram (DCD)

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Design Class Diagram

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Classifier

• A UML classifier is “a model element that describes behavioral and structure features”. Classifiers can also be specialized. They are a generalization of many of the elements of the UML, including classes, interfaces, use cases, and actors. In class diagrams, the two most common classifiers are regular classes and interfaces.

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Showing UML Attributes

• Attribute text notation such as: currentSale : Sale, Association line notation, or both

• <visibility> name : type multiplicity = default {property string}

• Attributes are assumed private if no visibility is given

• Arrow shows that the object where the arrow starts has one object of the object to which it points.

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UML Attributes

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UML Attributes

• Multiplicity shows how many on the left can associate with how many on the right

• Role name• Attributes are assumed private unless

otherwise noted

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Attribute Text vs. Association Lines• Use text notation for primitive data types,

even things like Zip codes that may have components but are not complex

• Use association for everything else.

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Collection Attributes

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Note Symbols• A UML note symbol is displayed as a dog-eared

rectangle with a dashed line to the annotated element; they’ve already been used throughout the book. A note symbol may represent several things, such as:– a UML note or comment, which by definition have no

semantic impact– a UML constraint, in which case it must be encased in

braces ‘{…}’ – a method body—the implementation of a UML

operation

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Operations and Methods

• A method is the implementation of an operation

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The Create operation

• This is a constructor call• You can use <<constructor>> to make this

explicit

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Keywords

• A UML keyword is a textual adornment to categorize a model element

• Keywords include <<actor>>, <<Interface>>, [abstract], [ordered]

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Stereotypes, Profiles, Tags• Stereotypes are also shown in guillemets

symbols . They are not keywords. A stereotype represents a refinement to an existing modeling concept

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Properties and Property Strings

• A property is “a named value denoting a characteristic of an element

• Textual approach is to use the UML property string {name1=value1, name2=value2} format, such as {abstract, visibility=public}

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Generalization

• A taxonomic relationship between a more general classifier and a more specific classifier

• This can imply inheritance, but not at the conceptual level.

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Dependency

• Similar to association. Indicates that a client element has knowledge of another supplier element, and a change in the supplier could affect the client

• (Supplier and client are descriptive terms, not classes)

• Dependency lines are common on class and package diagrams

• Use to depict global, parameter variable, local variable, and static-method dependency

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Types of Dependency

• Having an attribute of supplier type • Send a message to a supplier• Receiving a parameter of supplier type• Supplier is a superclass or interface• Indicated by a dashed line arrow

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Interfaces

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Composition Vs. Aggregation

• Aggregation is a vague association suggesting whole-part relationships. No meaningful semantics in UML versus association.

• Composition, or composite aggregation, is a strong kind of whole-part relationship.

• Implies that an instance of the part belongs to only one composite instance of the whole

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Composition

• For example the Monopoly board consists of 40 squares

• A square can be part of only one board at any time.

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Constraints

• Constraints is a restriction on a UML element.• Shown as text between braces• {size > 0}

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Qualified Association• Uses a qualifier to select an object or set of

objects from a larger set• For example, looking up something in a

HashMap

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Association Class

• Allows you to treat an association as a class, such that it can have attributes

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Singleton Class

• Only one instance of a Singleton class (pattern explained later) is ever instantiated.

• For example, your main class in most programs is a Singleton, although this may not be its dominant pattern.

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Template Classes and Interfaces

• These are equivalent to C++ or Java “generics.”

• That is, you can type a collection class.

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User-Defined Compartments

• In a class diagram you can define your own compartments:

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DataAccessObject

Id: int

doX();

Exceptions thrownDatabaseExceptionIOExeception

ResponsibilitiesSerialize and write objectsRead and deserialize objects

Active Class

• An active object runs on and controls its own thread of execution

• In UML, it is shown with double vertical lines on the left and right of the class box.

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