Ruben Jubeh ruben.jubeh@uni-kassel - ut

Design Patterns with FujabaIntense Course, 5th-9th October 2009

Ruben [email protected]

Kassel University

Department of Software EngineeringWilhelmshöher Allee 73

34121 KasselGermany

Fujaba Modeling & Design Patterns © 2009 Ruben Jubeh, Albert Zündorf, University of Kassel 2

Timetable

Monday, October 5th:10.15-11.45, room 40512.00-13.30, room 40314.15-15.45, room 405 (Exercise)

Tuesday, October 6th:10.15-11.45, room 40412.00-13.30, room 40414.15-15.45, room 405 (Exercise)

Friday, October 9th:10.15-11.45 room 40212.00-13.30 room 31514.15-15.45 room 315 (Exercise)


What we have learned yesterday

General Design Principles & Design Patterns Introduction

Modeling with Fujaba4Eclipse

More Design Patterns... with live coding Strategy Pattern

Fujaba4Eclipse: Modelling Methods Simple Control Flow, Statement Activities Creating and Deleting Objects

More Design Patters: Composite Pattern (with Fujaba4Eclipse) Visitor Pattern (in Java)

Exercise 1: Strategy Pattern

Homework 1: Implement Composite and Visitor Pattern in Java or Fujaba4Eclipse


Overview

More Design Patterns... #4-8: DP #4: Visitor Pattern DP #5: Adapter Pattern DP #6: Strategy and Hook Pattern DP #7: Chain of Responsibility DP #8: State Pattern

Fujaba4Eclipse Story Driven Modelling continued...

More Design Patterns... #9-11: Template Method Pattern Decorator Pattern Observer Pattern (Listener)

Fujaba4Eclipse: PropertyChange-Mechanism

Exercise 2, Homework 2


Exercise 1

Implement the single Alarm / delegation example from day1/slide16 in Java: Use the singleton pattern for the class House

Write a method, which instanciates all types of alarms, adds them individuallyto the house and calls house.alarm() each time (Strategy Pattern)

Model the same example in Fujaba4Eclipse (hint: use a different packagename)

Change your main()-Method to use the generated code (or model one)

Use the eDOBS to visualize your object structure! Can you observe any differences between plain java and generated classes?


Live modeling

of Exercise 1

House

run ()alarm ()

FlashLightalarm()

Sirenalarm()

MailAlarmalarm()

alarmDevice AlarmDevicealarm ()

cardinality here? 1 ? n ?we start with 1 ...


Homework 1:

Implement Abstract-, RegularFile and Directory using the CompositePattern as shown before (either in plain java or as Fujaba4Eclipsemodel, assume unix-style filesystem, you might omit Root/Drive)

Delegate RegularFile(String name), child computation, getName() andgetFileSize() to java.io.File in the class RegularFile

Implement findAll() and countFiles() like shown in the lecture / session3! How many files are there?

Implement findAll(String extension) - should list only files with the givenfile extension. How can this be combined with countFiles()? Find asolution that prints just the number of .java-Files!

Count the files in the current directory by calling traverse(new RegularFile(“.“), visitor); using theCountFilesVisitor. How many are there?

Write a SummarizeFileSizesVisitor ! What is the summarized size of the files in the current directory? Advanced: Add a file extension filter to the CountFilesVisitor. How many *.java-Files are there?


Visitor motivation

Now we want to implement some operations: Count all files recursively Summarize the file size of all files ... Find empty directories ... Difficult with the current approach!!!

Decouple tree traveral from operation (e.g.System.out.print)

Allow different operations, group then in classes

Operations might be interested only in a certain type of thetraveral elements


Implementing

Visitor Pattern

Live

(CountFilesVisitor and

FindEmptyDirectoriesVisitor)


DP #4: Visitor Pattern - Specification

Pass a Visitor to all Elements while iterating/traversal

Elements call corresponding visit()-Method

Consequences: Benefits and Drawbacks Separation of concern Adding new ConcreteElement is hard, operations not Encapsulation? Known Usages: Parser, e.g. javacc


Adapter Pattern - example and motivation

Run dpexamples.day2.adap.SimpleTreeViewer Shows a graphical hierachical tree of data

We want to adapt to java.io.File now, to present thedirectory tree Which is a hierarchical tree as well!

Problem: Swing expects TreeNode with its operations butjava.io.File provides differrent methods!

Solution: Adapter, which satisfies (implements) the treeinterface but delegates to java.io.File!


Live implementation

of the Adapter Pattern

TreeViewer -> java.io.File(might be helpful for homework 1)


Adapter Pattern: Specification

Adapt between Target and Adaptee

Either use inheritance or delegation

Known Uses: Heavily in the Eclipse Framework


Hook Pattern

Additional functionality can be added at runtime

Delegation to many Handlers, might be ordered

(See HouseAlarm Example of Exercise 1)

Example:

House

run ()alarm ()

FlashLightalarm()

Sirenalarm()

MailAlarmalarm()

alarmDevice AlarmDevicealarm ()n<< ordered >>

public void alarm(){ ...for (a : alarmDevices){alarm.alarm();

} ...


Hook Pattern : Specification

Delegate Request to many objects

Only (abstract) supertype known to Client

Example: Java Servlets (multiple instances), Eclipseplugins...


Chain of Responsibility

Based on Hook: Handlers as well But handlers itself might be linked

Stop when one Handler received the request Might use return value

Example:House

run ()alarm ()

FlashLightalarm()

Sirenalarm()

MailAlarmalarm()

alarmDevice AlarmDevicealarm ()1

< next1:1


Live implementation

of CoR

in Fujaba4Eclipse / HouseAlarm


Modeling Methods with Fujaba4Eclipse

=>


Story / Activity Diagrams

Start -> Control Flow -> Stop Transitions in between

Statement Activity for plain Java Code

Story Pattern (aka Activity) contain Object diagrams Specify a Graph Transformation

Black: match Green: create Red: destroy

Objects might have modifiers: Create, Destroy „bound“ Objects omit the Type

Links between objects Same modifiers - create (implicit), destroy


Advanced Modelling

Success- and Failure-Transition

Each-time-Activity for iterations Doubleclick or Edit Story Activity Might use each-time- and end-for-all-Transition

Collaboration statements Number for Timeflow, enter method

Constraints

You can verify whether the method does what you expectby looking at the generated source code (at first)!


State Pattern

Based on Strategy Pattern - again to-one association Eliminate if/elseif/else-chains

But Strategy gets changed systematically: Each State is a different instance States collaborate

Example: HouseAlarm Each alarm should be used only three times, then it

should change to the next alarm automatically


Live implementation

of State Pattern

in plain Java / HouseAlarm


State Pattern: Specification

Specification: same as Strategy... State change left to implementation

Known Uses: Various StateChart-Implementations, e.g. in Fujaba Many extensions like hierarchy, transitions, events...


SDM / Activity-Diagrams (recapitulation)

Activities and Transitions

Start with Class- and Method-Name

Activities for working steps

Transitions (with Guards like success,failure...) for control flow

Stop, Diamond...


SDM Activity Diagrams Ref.: Control Flow

Activities

start activity

stop activities

rule acitivities

code activities

branch activities

Transitions without Guard [success] and [failure] [[each time]] and [[end]] [boolean condition] [else] [exception]


SDM Activity Diagrams: Control Flow (2)

Activities

start activity

stop activities

rule acitivities

code activities

branch activities (diamond)

Transitions without Guard [success] and [failure] [[each time]] and [[end]] [boolean condition] [else] [exception]


Advanced SDM

Constraints

Collaboration Statements Ordered Might declare, loop, iterate...

Object constraints: Negative Objects: a object that must not be there Optional Objects: a object that might be there (for a operation)

Links: first, last, index, key...

Virtual Paths

Alternatives modeling iterations Foreach vs. Success/Failure-Transitions


SDM - Execution Engine Enter a Activity...

Search and match Objects Take over all bound objects from previous steps or parameters Follow links... Evaluate attribute assertions Bind matched objects to local variables

Evaluate Constraints On Error: Do nothing more, follow Failure-Transition

Create Objects, Links

Assign Attributes

Invoke Collaboration Statements Set local Variables

Delete Objects, Links

next Transition...



Template Method Pattern (aka Single-Hook)

Motivation Algorithms with a fixed outer structure But individual steps might vary

Example ImageConverter:

Collect all Files in a Directory... then, on each idividual file: Open, read, adjust brightness/contrast Transform (rotate by 90degrees if needed Compress and write

Here: AlarmDevice.alarm() splits into start and stop


Live implementation

of the

Template Pattern

in plain java using

AlarmDevice start()/stop()


Template Method Pattern : Specification

Outer, general algorithm

Specialized steps

Consequences: Benefits and drawbacks Helps to have a defined structure No object-level composition

Known Uses: probably any abstract class :)


Decorator Pattern

Template Method doesn‘t help if we need to mix things Combine different open, transform and write operations Compose different transforms at runtime, each one encapsulated in

one class (GeneralFileConverter)

A deeper look into the transform() of the ImageConverter Remove red-eyes-effect Adjust Brightness/Contrast Rotate by 90degrees

Idea behind the Decorator: Keep the interface ( transform() ) But delegate to individual objects

The Java API contains a good example: Streams


Showing the decorator live

with java.io.*Stream


Decorator Pattern : Specification

Delegate to objects

Based to Strategy (delegation chain of length 1)

Consequences: Runtime flexibility Lots of Objects

Known Uses: java.io.*Stream, -Reader and -Writersubclasses


Observer Pattern

Basic Pattern behind MVC

To-many relationship between subject and observers

aka Publish-Subscribe-Protocol

Example: One Sensor in the House notifies all AlarmDevices

House

run ()alarm ()

FlashLightalarm()

Sirenalarm()

MailAlarmalarm()

alarmDevice AlarmDevicealarm ()

Sensornotify()


Live implementation

of the Observer Pattern

with HouseAlarm


Observer Pattern : Specification

Observers register at the Subject

Subjects changes are delivered to all Observers

Updates: Push- vs. Pull

Known Uses: GUI/Widget Libraries, e.g. various Listeners in Swing


PropertyChange Mechanism

General JDK mechanism (some default implementation ismissing), basically the Observer Pattern

Slighty different Terminology: Listener, Source, Property

adopted in the Fujaba Code Generator Uses Constants in the generated Code Robust

Requires <<JavaBean>> stereotype in each class whichshould fire events

All setters fire accordingly... oldValue, newValue


Lets have a look...


Exercise 2

Start with your exercise from yesterday or download andextract workspace.dp2.zip .

Extend the HouseAlarm model in Class Diagram „Day2:HouseAlarm as Hook / CoR“ with the (modified) Chain-of-Reponsibility-Pattern Choose either CoR-with-ordered-to-n-assoc (easier,

Slide n) or CoR-with-next-link (Slide n2) delegate alarm() to the first active AlarmDevice

What could your program do if no AlarmDevice isresponsible? Implement a solution that ensures that thealarm() won‘t get lost


Implementation of Exercise 2:

Chain of Responsibility

with HouseAlarm


Homework 2

Start with the Class Diagram „Homework2a: Filesystem“: Model the Visitorpattern! That means: Add a traverse-method to FileSystem (Use a foreach-activity. Might use

recursion) Add an abstract Visitor interface Let the concrete classes accept the visitor during traversal and let them

call the visitor finally Optional: implement a ListAllFilesVisitor

Start with plain java HouseAlarm (Homework/src/dpexamples.homework2b) Let MailAlarm.alarm() throw a new RuntimeException(“Mail server down!“).

Implement the state pattern by adding some logic which switches to theSiren then. Where should the try/catch be? Where is the strategyexchange?

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Ruben Jubeh ruben.jubeh@uni-kassel - ut