1. Mini seminar intro

by Leonid Maslov on Feb 21, 2011

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The first seminar in the mini-seminars periodical sessions I've prepared and lead in my spare time while being employed at Exigen Services. Kudos, guys! ...

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The first seminar in the mini-seminars periodical sessions I've prepared and lead in my spare time while being employed at Exigen Services. Kudos, guys!
Since these presentations were spare time hobby - I've decided to share them :)
Hopefully someone will find them useful.

The intro is - what designs patters are about, some simple examples and a lots of colorful images.

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1. Mini seminar intro — Presentation Transcript

Mini Seminars/Design patterns...
Leonid M.

Veicināt atvērtu komunikācijas vidi
Identificēt stipras / vājas eksistējošas ekspertīzes puses
Efektīva dalīšanas ar interesantu / noderīgu / jaunu informāciju
Mini semināru mērķi

Design Patterns

Theory
Name a few: Strategy, Bridge ...
Pattern vocabularies: Patterns of Enterprise Application Architecture …
“Not a pattern” pattern
Anti-patterns
Design Puzzles
Testability & Patterns: Google Testing Blog

Mini seminar #2: Best Practices

Mylyn & Attlassian connectors
… ?

Mini seminar #1: Content

Each pattern describes a problem which occursoverand over again in our environment, and then describes the core of the solutionto that problem, in such a way that you can use this solution a million timesover, without ever doing it the same way twice
Christopher Alexander, Sara Ishikawa, MurraySilverstein, Max Jacobson,Ingrid Fiksdahl-King, and ShlomoAngel.A Pattern Language. Oxford UniversityPress, NewYork, 1977.
Design Pattern

Design Pattern
Name

Encapsulate what varies
Favor compositon over inheritance
Program to interfaces, not implementations
Strive for loosely coupled designs between objects what interact
Turtles all the way down

Shared vocabularies: benefits

Recognition
Communication compactness
Code readability
Identified consequences and impacts
Best practices reused

GOF
Name
Intent
Also Known As
Applicability
Structure
Participants
Collaborations
Consequences
Implementation
Sample Code
Known Uses
Related Patterns
Definition / Vocabularies

Strategy pattern
or

Synonyms: Policy
Intent: Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Strategy

Sample code
Example #1:
class StrategyExample {
public static void main(String[] args) {
Context context;
// Three contexts following different strategies
context = new Context(new ConcreteStrategyMultiply());
int resultA = context.executeStrategy(2, 3);
context = new Context(new ConcreteStrategyAdd());
int resultB = context.executeStrategy(resultA, 1);
}
}
Example #2: Code snippet from java.io.File
public String getAbsolutePath() {
return fs.resolve(this);// NT file system, Unix file system, etc…
}

JDK
java.net.URL – use protocol handlers as strategy to open connection
java.io.File – use underlying file system as strategy to manage files
Eclipse
Almost everything is strategy. Why so?
…
Code next door

Adapter vsDecorator

Adapter

Synonyms: Wrapper
Intent: Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.

public class ApproverJiraUserAdapter implements ApproverResolveStrategy<User> {
private final ApproverResolveStrategy<String> delegator;
public ApproverJiraUserAdapter(ApproverResolveStrategy<String> delegator,
UserManager userManager) {
this.delegator = delegator;
this.userManager = userManager;
}
….
/*
* (non-Javadoc)
*
* @see
* com.exigen.jira.plugins.sr.approval.strategies.ApproverResolveStrategy#resolve(com.exigen.jira.plugins.sr.approval
* .strategies.StrategyContext, java.util.Collection)
*/
public List<User> resolve(StrategyContext context, List<User> resolventChain)
throws ApproversResolveException {
try {
log.debug("Converting to user objects");
return toUsers(getDelegator().resolve(context, toStrings(resolventChain)));
} catch (EntityNotFoundException e) {
throw new ApproversResolveException(e);
}
}
….
ESWIJI, live code sample
Client
resolve(..User ..)
List<User>
ApproveResolveStrategy<User>
resolve(..String ..)
List<String>
ApproveResolveStrategy<String>

JDK
java.io.OutputStreamWriter
java.io.StringReader
…
java.awt.event.MouseAdapter
…
Code next door

Synonyms: Wrapper
Intent: Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Decorator

Decorator, GOF sample(Best illustration ever)

JDK
java.io.BufferedInputStream
java.io.*
javax.swing. JScrollPane
Code next door

What’s the difference?
Adapter vsDecorator

Chain of Responsibility
Intent: Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles.

public class WelcomeFilterimplements Filter
{
public void init(FilterConfig filterConfig)
{
welcome = filterConfig.getInitParameter("welcome");
if(welcome == null)
welcome = "index.html";
}
public voiddoFilter(ServletRequestrequest, ServletResponseresponse, FilterChainchain)
throws IOException, ServletException
{
String path = ((HttpServletRequest)request).getServletPath();
if(welcome != null && path.endsWith("/"))
request.getRequestDispatcher(path + welcome).forward(request, response);
else
chain.doFilter(request, response);
}
…
}
Code sample

JDK
java.util.logging.Logger
javax.servlet.Filter
Code next door

Application: Email spam filtering system. Both HTML and Text formats should be supported.
Multiple spam recognition algorithms are present and several could be used simultaneously.
Multiple weekly report approaches should be supported: XML, HTML files on filesystem;+ email  with report attachment.
Pattern puzzle

Questions

1. Mini seminar intro

by Leonid Maslov on Feb 21, 2011

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1. Mini seminar intro — Presentation Transcript