Unit 0 Appendix D UML at a Glance

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Unit 0Appendix D

UML at a Glance

Summary prepared by Kirk Scott

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Design Patterns in JavaAppendix D

UML at a Glance

Summary prepared by Kirk Scott

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UML Notation for Classes

• First, a UML diagram will be given• It is preceded by the features it includes• It is followed by a more detailed, point-by-

point explanation of the features

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Features

• Packages– Tabbed boxes– Dot notation

• Classes– Rectangles– Name, instance variables, constructors, methods

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• Methods– Access modifiers, -, +, #– Return type– Parameters

• Static methods– Underlined– Or dot notation with class name

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• Notes– Dog-eared boxes

• General rule– A UML diagram can be as complete and detailed

or as sparse as desired– The goal is to convey what is necessary without

needing to convey what is not important

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Packages

• Indicate a package by putting its name in a “tab” at the upper left of a rectangle which contains the elements (classes, etc.) of the package

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Classes

• Draw a class by centering its name in (at the top of) a rectangle

• Note that UML doesn’t require that everything be shown in a diagram

• The diagram can be selective, showing only what’s necessary to explain the topic at hand

• The diagram may simply give the name of the class, or it may include other information

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• If a class belongs to a package, but the package itself is not diagrammed as a tabbed rectangle, the class’s name can include the package name using dot notation:

• packagename.classname

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• Class diagrams can show instance variables in a second subdivision of the rectangle, below the one with the name

• Not all instance variables of a class need be listed

• The names of variable are given followed by a colon, followed by a type

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• Class diagrams can show (constructors and) methods in a third rectangle, below the one with the instance variables

• Not all methods of a class need be listed• A listing of a method would include its name

and a pair of parentheses

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• If the method takes a parameter, within the parentheses the name of the parameter would be given, followed by a colon, followed by its type

• If the method returns a value, the parentheses are followed by a colon, which is followed by the type of the return value

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• Both instance variables and methods can be marked to indicate what access modifier they have

• Private things are preceded with a “-”• Public things are preceded with a “+”• Protected things are preceded with a “#”

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• Static methods are indicated by underlining• In addition, static methods can be noted using

dot notation, giving the name of the class, followed by a colon, followed by the method signature

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Notes

• Notes can be added by drawing a dashed line from the item in question to a dog-eared rectangle

• Notes can be code, constraints, or comments• Notes can be used wherever needed or

desired in a UML diagram

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Additional Class Notation and Class Relationships



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Features

• Abstract classes and methods– Italicize

• Relationships– Any line indicates some relationship

• Inheritance– Solid line with closed, hollow arrowhead from

subclass to superclass

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• Aggregation or composition– Solid line with diamond from “having” to “had”

class• Reference/Navigability– Solid line with open (feathered) arrowhead from

the one with the reference to the one referred to• Dependencies without references– Dashed line with open arrowhead

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Additional Class Notation

• Italicize the names of things that are declared abstract, like methods and the classes that contain them

• Underline the names of static methods

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Class Relationships

• A line, in general, indicates some relationship between classes

• Conventions such as dashed or solid lines, and what kind of symbol they have on the end, indicate what the relationship is

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Inheritance, or Superclass-Subclass Relationships

• Use a solid line and a closed, hollow arrowhead to point from a subclass to its superclass

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Aggregation and Composition

• Use a solid line with a diamond to indicate that one or more instances of one class contain one or more instances of another

• The line can be labeled with numbers indicating the cardinality of each end of the relationship

• A white or black diamond determines whether this is aggregation of composition, respectively

• Under composition, the parts can’t exist without the whole

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References and Navigability

• If two classes are connected by a simple line, this would indicate that one of the classes has an instance of the other as an instance variable

• In order to make this clear, a reference from one class to an instance of another is indicated with a solid line with an open arrowhead

• The official term for this is navigability, the object referred to is reachable through the code of the object which refers to it

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Class Dependencies without References

• Classes may also have dependencies that are not determined by an object reference

• Such dependencies are shown with a dashed line and an open arrowhead

• The book illustrates such a dependency with a class that calls a static method of another class

• The book also uses this notation to indicate the throwing of an exception, with the arrow pointing from the throwing class to the exception class

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Interfaces



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Features

• Interfaces– Rectangle with label “interface” in European

quotation marks– Dashed line with closed, hollow arrowhead from

class that implements to interface– Lollipops to avoid multiple lines in diagram

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Interfaces with Arrows

• You can show an interface by drawing a rectangle and labeling it with the name of the interface in European quotation marks

• A dashed line with a closed, white arrowhead from a class to an interface shows that the class implements the interface

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Interfaces with Lollipops

• The fact that a class implements an interface can also be indicated by a short line from it to a small circle (a lollipop) labeled with the interface name.

• This notation helps prevent a nightmare of criss-crossing lines in a diagram

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Interfaces and Abstract Classes

• The book makes this statement:• “Interfaces and their methods are always

abstract in Java. Oddly enough, interfaces and their methods do not appear in italics, unlike abstract classes and abstract methods in classes.”

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• Two observations can be made about the book’s statement:

• 1. If interfaces and methods are always effectively abstract, then there is no need to indicate that with italics or other notation. It is understood.

• 2. Purists might argue that interfaces and abstract classes are two different things anyway.

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Objects



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Features

• Objects– Rectangle labeled with name, underlined– Solid line with open arrowhead between objects

indicates a reference

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• Sequence diagrams– Rectangles for objects (at the top)– Dashed life-line from top to bottom– Narrow rectangles indicate method activations– Horizontal arrows represent calls– Object creation can also be shown

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Object Naming

• An object is represented by rectangle containing the name of the object

• More completely, it could be given as object name, colon, class name

• In the case of an unnamed object, it can be labeled with a colon followed by the class name

• Whatever naming convention is used, the name should be underlined

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Object References

• A line between two objects shows that one has a reference to the other

• Just like with this notation in classes, it should be a solid line with an open arrowhead going from the one having the reference to the one referred to

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Sequence Diagrams

• Static structure diagrams typically show the relationships between classes

• Sequence diagrams show the relationships between objects, namely the calls between them, at run time

• Sequence diagrams, like static structure diagrams, can vary in level of detail

• They can show specific information about methods—or not

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• When doing sequence diagrams, each object has a dashed life-line, a dashed vertical line where time runs from top to bottom

• The calls from one object to another are indicated by solid lines with solid black arrowheads from the life-line of one object to the life-line of another

• The lines are labeled with the name of the method called

• In UML terminology, the calls are known as one object “sending a message” to another

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Object Creation

• One object creating another is shown using similar notation

• A solid line with a solid black arrowhead runs from the life-line of the creating object to the rectangle representing the created one

• This arrow is labeled with what is known as a stereotype, the word “create” in European quotation marks

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Objects and Threads

• The last point on this topic is rather obscure• In other words, we will never have a use for it in

this course• If the box representing an object is bold-faced,

this means that the object is active in a thread, process, or computer other than the one in which the other objects in the diagram are active

• In other words, this is a way of indicating remote calls, for example

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States



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Features

• State– Rectangle with rounded corners, labeled

• Transition– Solid line with open arrowhead, labeled

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• A state is given as a rectangle with rounded corners containing the name of the state

• Transitions between states are given as solid lines with open arrowheads labeled with the name of the transition

• State charts do not necessarily map directly to a class or object diagram in particular application code, although this is possible

• This will come up in chapter 22 on the State design pattern

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The End

Unit 0 Appendix D UML at a Glance

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