Unified Modeling Language UML Much of the information in this presentation is adapted from Wikipedia

Open Source Software DIA can be used to create UML diagrams http://dia-installer.de/download.html You may want to start the program, if you like to follow along.

Example

Example

Example

Questions you may ask… SO, you need to get up to speed in a hurry on an existing system. OR, you want to quickly communicate the overall design of a system (i.e., the system architecture*) to other programmers. What’s important to know? What classes are involved? What’s the purpose of each class? (what methods can I call so the class “works” for me) What’s the relationship between classes? * covered in more detail during field session

What is UML? The Unified Modeling Language (UML) is an open method used to specify, visualize, modify, construct and document the artifacts of an OO software project. UML 1.0 Spec proposed in January 1997 UML 1.1 adopted in November 1997 UML 2.0 adopted in 2005

What is UML (continued) UML is not a development method. It is compatible with leading OO software development methods. System model includes diagrams + “semantic backplane” – written use cases etc. UML diagrams represent two views of system model: Static structure of the system using objects, attributes, operations and relationships. The structural view includes class diagrams and composite structure diagrams. Dynamic (behavioral) behavior. Shows collaboration among objects and changes to system state, represented via sequence diagrams, activity diagrams and state machine diagrams.

UML – How? UML 2.0 has 13 types of diagrams divided into 2 categories We’ll only study Class Diagrams, State Machine Diagram also useful.

Let’s try DIA Be sure you’re in UML mode Use tool tips to identify buttons Select Class icon Click to place on diagram Double-click to edit details We’ll primarily use Attributes and Operations (you think of these as variables and methods) switch to UML

Class Diagram Shows system classes, attributes, relationships among classes Class diagrams are static -- they display what interacts but not what happens when they do interact. Class name at top of diagram Attributes in next section. # indicates protected, - indicates private + indicates public, ~ indicates package Methods (operations) in bottom section. + indicates public., - indicates private. Common to omit getters/setters

Another class Attributes may specify a type Class variables (i.e., static) are underlined Accessibility is indicated with +, -, # Parameters (with optional types) can be specified

Translating to code public class Student { protected String name; // type not in UML private String address; // make reasonable private String email; // assumptions public boolean isEnrolled() { return true; } // body not specified, return needed to compile } public class GamePanel { public static final int CELL_SIZE = 20; private int whoseTurn; public void drawBoard (Graphics g) { } } final is a low-level detail, no consensus on whether/how to represent in UML How do we know it’s final? Class convention of ALL_CAPS

Why are we doing this again? It’s good to think about the high-level structure of your program before you begin to code. If only two classes in your system, probably not needed. What if you have 20 interacting classes? How am I supposed to figure this out??!!

But how do these classes work together? Need to specify relationships between classes Inheritance. Also called generalization and specialization. Association. Means an instance of one class can send a message to an instance of another. Class sending the message must have access to the receiver (e.g., via a pointer, reference etc). Aggregation. Whole/part relationship. (e.g., car has 4 wheels; wheels may outlive car). May be called a “has-a” relationship. Composition. Like Aggregation except lifetime of ‘part’ must match lifetime of ‘whole’ (e.g., car has a carburetor) Dependency One class relies on another, but doesn’t contain a variable. Composition and Aggregation are types of associations; distinction is not that critical.

Inheritance in UML Called a generalization relationship General Open triangle, points to parent Specific HINT: To remember direction, think that a child has only one parent, a parent may have many children. Our diagram has only one arrow – must point to parent.

Translate to Code public class Book { private String title; private String author; } public class Textbook extends Book { private String course; public class Dictionary extends Book { private int numWords; NOTE: We do not repeat Title and Author in the child classes… instance variables are all inherited – GENERAL RULE: Don’t clutter the diagram!

Here’s an association in code public class Student { private String name; private Dog dog; public Student(String name){ dog = new Dog(); } public void takeAWalk() { dog.bark(); public class Dog { public void bark() { System.out.println("Woof"); } Note that Student has a variable of type Dog – but it does not appear in the UML as an attribute. Why? How does this help us design? Functions are put in various classes. Where does the functionality live? How can our classes work together to create a solution?

UML relationships Association. Arrow indicates navigability. Include arrow if unidirectional If no arrows, indicates bidirectional May have multiplicity (e.g., 0 .. *) May have role (e.g., subscriber)

Here’s an aggregation in code public class Car { private ArrayList<Wheel> wheels; } public class Wheel { Note the open diamond attached to the owner. We will not make the distinction between aggregation and composition – these look no different in code.

Enumerated type + code + dependency Dotted line is a dependency. Weaker association. Notice WeekendDays is a parameter, but not an attribute. public enum WeekendDays { SATURDAY, SUNDAY } public class Event { public void addParty(String name, WeekendDays day) { … } }

Abstract Classes, Interfaces and Static Abstract class and method names are normally italicized (must set the Properties -> Style in DIA) An interface is a stereotype, show inside << …>> Indicate static methods/variables with a $ or underline

Translate to Code public abstract class Shape { private int x, y; public abstract void draw(); } public interface Comparable { public int compareTo(Object o); } public class Book implements Comparable { private String title, author; public int compareTo(Object o) { …. }

Bookstore Example

Package Example Note that sometimes we just want class names – in DIA, uncheck Attributes visible and Operations visible

Another Example