JNK Java

Concurrency in Java 6

2011-10-27T13:48:00.000-07:00

Threads are lightweight processes that share the same memory space. A scheduler can swap between threads. Java uses preemptive multithreading, where the OS is responsible for swapping threads.
Java 5 has introduced a significant new paradigm to handle threads, compared to the primitive concurrent commands of pre version 5. It is recommended that you use the new java.util.concurrent.* package. In the following I show the thread commands for Java pre-version 5 and post-version 5.

Java 1-4	Java 5-7
Thread Creation
public class MyThread extends Thread { public void run() { // your concurrent task here } } MyThread thread = new MyThread(); thread.start(); or public class MyTask implements Runnable { public void run() { // your concurrent task here } } Thread thread = new Thread(new MyTask()); thread.start();	public class MyTask implements Runnable { public void run(){ // your concurrent task here } } // Creates new threads as needed and destroys old threads ExecutorService exec = Executors.newCachedThreadPool(); // Keeps a permanent total number of threads ExecutorService exec = Executors.newFixedThreadPool(5); // Like newFixedThreadPool but only for one thread ExecutorService exec = Executors.newSingleThreadExecutor(); // To be scheduled, to replace java.util.Timer ExecutorService exec = Executors.newScheduledThreadPool(); // Like before but for one thread only ExecutorService exec = Executors.newSingleThreadScheduledExecutor(); exec.execute(new MyTask()); exec.shutdown(); int processors = Runtime.getRuntime().availableProcessors(); ExecutorService executor = Executors.newFixedThreadPool(processors); Future<Integer> futureResult = executor.submit( new Callable<Integer>() { public Integer call() { // long running computation that // returns an integer } }); Integer result = futureResult.get(); // block until result is ready exec.shutdown();
Critical sections
public synchronized void method() { // same as synchronising on "this" // which is dangerous as another // thread could get hold of "this" // and block your code. // When the lock is acquired for // the synchronized block, other // synchronized methods and // critical sections in the object // cannot be called. } // use this instead // In Java, every object contains a “monitor” // that can be used to provide // mutual exlusion access to critical sections of code. private final Object monitor = new Object(); public void method() { synchronized(monitor) { // your critical section here } }	import java.util.concurrent.locks.; private final Lock lock = new ReentrantLock(); public void method() { // cannot be interrupted lock.lock(); // can be interrupted // lock.lockInterruptibly(); try{ // your critical section here } finally { lock.unlock(); } } // can try lock public void method() { boolean locked = lock.tryLock(); if (locked) { try{ // your critical section here } finally { lock.unlock(); } } else { // do something else } } import java.util.concurrent.locks.; private final ReadWriteLock lock = new ReentrantReadWriteLock(); public void doWrite() { lock.writeLock().lock(); try { // your critical section here } finally { lock.writeLock().unlock(); } } public void doRead() { lock.readLock().lock(); try { // your critical section here } finally { lock.readLock().unlock(); } }
Thread interactions
private final Object lock = new Object(); // must lock on the same object private volatile boolean notified = false; public void doWait() { synchronized(lock) { while(!notified) { // avoid spurious wakeups try { // releases the object lock and waits // until it gets notified // otherwise the notifying thread could // never acquire the lock! lock.wait(); } catch(InterruptedException e) { } } //clear signal for next waiting thread and continue running notified = false; } } public void doNotify() { synchronized(lock) { notified = true; // sends a message to a thread waiting on the object lock lock.notify(); // sends a message to all the threads waiting on the object lock // lock.notifyAll(); } }	import java.util.concurrent.locks.*; private final Lock lock = new ReentrantLock(); private final Condition condition = lock.newCondition(); private volatile boolean notified = false; public void doWait() { lock.lock(); try{ while(!notified) { condition.await(); // like wait(), releases // the lock and suspends current thread } } finally { lock.unlock(); } notified = false; } public void doNotify() { lock.lock(); try{ notified = true; condition.signal(); // like notify() // condition.signalAll(); // like notifyAll() } finally { lock.unlock(); } } final CountDownLatch latch = new CountDownLatch(3); ExecutorService exec = Executors.newSingleThreadExecutor(); exec.execute(new Runnable() { public void run() { try { // puts it into WAITING state latch.await(); // until latch == 0 } catch (InterruptedException e) { Thread.currentThread.interrupt(); return; } } }); for (int i=0; i<3; i++) { Thread.sleep(1000); latch.countDown(); // --latch; } final Semaphore semaphore = new Semaphore(3); ExecutorService exec = Executors.newSingleThreadExecutor(); exec.execute(new Runnable() { public void run() { try { semaphore.acquire(); try { Thread.sleep(1000); } finally { semaphore.release(); } } catch (InterruptedException e) { Thread.currentThread.interrupt(); return; } } }); Also check: CyclicBarrier, Semaphore, Exchanger
Atomicity/Visibility
/* The volatile modifier can be used to mark a field and indicate that changes to that field must be seen by all subsequent reads by other threads, regardless of synchronization.*/ public class MyClass implements Runnable { private volatile boolean finished = false; public void finish() { finished = true; } public void run() { while(!finished) { // .. do processing } } }	import java.util.concurrent.atomic.*; public class Counter { private AtomicInteger value = new AtomicInteger(); public int next() { return value.incrementAndGet(); } } java.util.concurrent.atomic package: AtomicBoolean AtomicLong AtomicInteger AtomicReference
Periodic Tasks
try { Thread.sleep(1000); // or TimeUnit.SECONDS.sleep(1); } catch(InterruptedException ex) { Thread.currentThread().interrupt(); // set interrupted status to true break; }	TimerTask task = new TimerTask() { public void run() { // your concurrent task here } }; Timer timer = new Timer(); timer.schedule(task, 1000, 1000); // (TimerTask, long delay, long period) // Better use this instead of java.util.Timer ExecutorService exec = Executors.newScheduledThreadPool(); // or this ExecutorService exec = Executors.newSingleThreadScheduledExecutor(); new javax.swing.Timer(1000, new ActionListener() { public void actionPerformed( ActionEvent evt) { //...Perform a task... } }).start();
Concurrent Collections
Sets	CopyOnWriteArraySet, CopyOnWriteArrayList, ConcurrentSkipListSet
Maps	ConcurrentHashMap, ConcurrentSkipListMap
Queues	BlockingQueue, ConcurrentLinkedQueue, ArrayBlockingQueue, LinkedBlockingQueue, PriorityBlockingQueue, DelayQueue, SynchronousQueue, BlockingDeque, LinkedBlockingDeque

Here's an example of how to use the new API:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ThreadInteractions implements Runnable {

    private final Lock lock = new ReentrantLock();
    private final Condition condition = lock.newCondition();
    private volatile boolean notified = false;

    public void doWait() {
        System.out.println("Awaiting ...");
        lock.lock();
        while (!notified) {
            try {
                // like wait(), releases the lock
                // and suspends current thread
                condition.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
        notified = false;
        System.out.println("Resuming ...");
    }

    public void doNotify() {
        lock.lock();
        try {
            TimeUnit.SECONDS.sleep(1);
            System.out.println("Notifying ...");
            notified = true;
            condition.signal(); // like notify()
            // condition.signalAll(); // like notifyAll()
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void run() {
        this.doWait();
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        ThreadInteractions obj = new ThreadInteractions();
        // a thread executes doWait()
        ExecutorService exec = Executors.newSingleThreadExecutor();
        exec.execute(obj);
        exec.shutdown();
        // the main thread executes doNotify()
        obj.doNotify();
    }
    
}

A thread, created by ExecutorService, calls the doWait() method, while the main method calls doNotify(). Here's the output.

Awaiting ...
Notifying ...
Resuming ...

It is more secure to use condition.signalAll() instead of condition.signal(). For that reason, the notified flag is set back to false in order for the next thread (not in this example however) to set it back to true and the next thread to be notified.

References

Jenkov, J., Introduction to Java Concurrency / Multithreading, http://tutorials.jenkov.com/java-concurrency/index.html
Eckel, B. (2007), Thinking in Java, 4th Edition, Prentice Hall.
Kabutz, H. (1999-2011), Newsletters

Java Open Spaces Conference 2011 in Chania/Crete

2011-09-02T10:24:00.000-07:00

Unfortunately, it's over. A conference different than others, an un-conference! The Java Open Spaces Conference, or Java Specialists Symposium took place from 29th of August till 1st of September 2011 in Perle Resort Spa Hotel at Chania/Greece. A conference different than others. The theme for our 2011 Java Specialists Symposium was: Making Java Fun Again.

An Open Spaces Conference

The conference was based on the principle of Open Spaces (thanks to Kim and Kate Tucker). In short, this means that we didn't invite key speakers, but the participants organised themselves to suggest topics of interest. This was the reason that no schedule was published even till the last day before the event. However, as you can here, the magic of open spaces conferences worked and the participants organised themselves to present very interesting and advanced topics. Heinz Kabutz, Kirk Pepperdine, Ben Evans, Michael Hunger, Dimitris Andreadis, Sven Reimers, just to mention a few, led some very interesting discussions on various topics. The outcome of the un-conference will be published under the Creative Commons license.

Excursions

A number of excursions in the afternoon followed the morning sessions. This added substantially to the coherence of the group. The participants enjoyed them and attached to each other. We went to some secret beaches, we swam, we ate traditional Cretan food, just amazing, and for those who preferred something else than sight-seeing there have been programming sessions (puzzlers!) in the evenings. Heinz Kabutz offered his house for a BBQ on Wednesday evening which contributed to a great atmosphere!

The participants loved the whole event. It was a combination of everything: conference, fun, sun, sea, great food, great company. What else can one ask? Ideal for you and your family. See you again next year!

FOSDEM 2011

2011-02-13T13:38:00.001-08:00

Another FOSDEM (Free Open Source Developers European Meeting) conference took place in the same location, the Universite Libre de Bruxelles (ULB) in 5-6 February 2011. A lot of participants, really, most of the rooms were full and you had to queue a lot of time in advance in order to find a chair to sit.
As a result I missed some interesting talks. A lot of stands of companies too, of OSS but also of OSH (Open Source Hardware) this year.
Some interesting talks:

HTML 5 by Robert Nyman and Christian Heilmann
Practical Go Programming, a new language by Google
Firefox 4: new features for users and developers
Scala expressiveness
State of OpenJDK

A number of insteresting stands, as already mentioned:

Manpremo a remote management system designed to allow you to control dozens of computers with ease and power
CACert - provides free certificates issued to you
OpenStreetMap
OBM is an enterprise-class messaging and collaboration platform for workgroup and enterprises which includes Groupware, messaging server, CRM, LDAP, Windows Domain, smartphone and PDA synchronisation...
Yate - Yet Another Telephone Engine
Haiku-OS
BeagleBoard

A summary of the HTML 5 presentation follows.

HTML 5 introduces a lot of goodies like: autocomplete box, email text field, color and date picker, range controls , search bar, input validation, placeholders, autofocus etc. Its main advantage is that for the first time it standardises Javascript, that means you don't need to write different javascript code for the different browsers.
It introduces a Canvas to draw images, play videos etc.

canvas.getContext("2d");
 img = document.createElement("path/to/img");
 img.addEventListener() ...

Since SVG is also a very powerful library for vector graphics, what does Canvas bring more? Well, use Canvas for speed and SVG for interaction.

 <video controls><
<source src="..."  type="video/mp4" media="..."></source><
<video>

It provides a lot of methods for interacting with the video, e.g.

load(), canPlayType(type), play(), pause(), stop(), addTrack() // for subtitles

etc.
Using these methods you can interact with e.g. a Flash video which was a black box up to HTML 4. CSS3 allows you to interact with the video.
While HTML 4 is stateless, HTML 5 is statefull, i.e. it allows you to store session variables to the web storage.

sessionStorage.setItem(key, value);

localStorage.setItem(key, value);

There is also support for webSQL and indexedDBs but also many TODOs:

WebWorkers for multi-threaded Javascript
WebSockets for realtime multi-user interaction
Audio analysis
Face detection
Image generation
Server side rendering
Multi-touch interfaces
Device input support (e.g. cameras)

Check the speakers' blogs (found on top of this topic) for more information about these amazing features. And as they finished their presentation:

"We can't change history but we can change the future".

Java IDEs

2011-02-12T17:26:00.003-08:00

Useful tools/links

2011-02-12T17:26:00.001-08:00

Forums/BBs in Java
JPOX -> DataNucleus
New innovative Eclipse plugin for code exploration
Track Java web application logs in Firefox
Stripes 1.5 a presentation framework for building web applications using the latest Java technologies
Loom 1.0 an open source Java web framework that handles user input validation and HTML generation for enterprise applications of any size
Jerry Huxtable labs
Exjali : EXpressiveness JAva LIbrary - Inspired by the buzz around Java 7 and "new" JVM language (Groovy, JRuby, Scala, ...), Exjali is a small Java library, allowing more expressive statements without altering the language. Exjali includes some attempts for ranges of integers, SQL-like functions, IO facilities, functors and named parameters.
Ilog's blog
Jetbrains Teamcity
Multi-Thread Run-time Analysis Tool for Java
uDig, a GIS framework for eclipse
Tapestry, a framework for developing java web applications
SOAsocial is a social networking site where you can track socially relevant activities in the SOA community and also participate in polls and other applications.
Application Integration Through Mail Servers from the book Open Source ESBs.
JBoss RestEasy helps you to build REST WS applications
Web4J
Apache Tiles a templating framework to simplify web application user interfaces development
Spring WebFlow and Spring Workflow. Some other workflow engines in Java.
Selenium is a testing framework for your web application independent of the programming language you are using.
Openfire an XMPP Real Time Collaboration (RTC) server.
DocWeb a community Javadoc.
Alice an education software that teaches students computer programming in a 3D environment
Java API for KML (JAK) - can be found here or here.
Play Web Application Framework
Vaadin Java Framework for building web applications
JWt a Java web toolkit for web applications that can be deployed within standard Servlet containers
Javolution a library for real time applications
JfcUnit a swing unit test framework. A list of unit test frameworks can be found here.
OpenFaces
FreeBase an entity-based database for the MetaWeb or Semantic Web. Watch the video.
For those who work on SOA, there are two new standars, Service Component Architecture (SCA) and Service Data Objects (SDO). Project Apache Tuscany is an open source implementation of these standards from Open Service Oriented Architecture (OSOA).
Google O3D a (deprecated) API for creating rich interactive applications for the browser.

ACMQueue programming challenge

2011-02-12T17:25:00.001-08:00

Like last year, ACM has already published its challenge (ICPC) for this year and there remain only 1 day for the deadline to submit your player. Good luck!

Java is pass by value

2011-02-12T17:21:00.001-08:00

for both primitives and types. More information here.

Java Tutorial Examples

2011-02-12T17:18:00.001-08:00

http://www.java2s.com/Tutorial/Java/CatalogJava.htm

http://www.javapractices.com/

Java Design Patterns

2011-02-12T17:17:00.001-08:00

Java Design Patterns are annotations in order to declare the DPs in Java. From the author of Java Specialist's Newsletter.

XSS vulnerability in Tomcat Manager

2011-02-12T17:15:00.001-08:00

More information here.

Conferences

2011-02-12T17:08:00.001-08:00

LibreOffice

2011-02-12T17:04:00.001-08:00

LibreOffice 3.3 is out and is very fast. LibreOffice is the continuation of OpenOffice since Oracle plans to stop it.
ThinkFree Office

How to write unmaintainable code

2011-02-12T17:01:00.001-08:00

What an article.

The ultimate Java puzzler

2011-02-12T16:30:00.001-08:00

Find it here.

Rich Internet Applications

2011-02-12T16:20:00.001-08:00

When we talk about Rich Internet Applications (RIA), our mind goes to Ajax. Here are some useful links with Ajax libraries:

and IDEs:

Open Source Observatory and Repository (OSOR) Technical platform

2011-02-12T16:02:00.001-08:00

Open Source Observatory and Repository (OSOR) Technical platform is EU's equivalent to Sourceforge. License is EUPL.

EU: Open Source Initiative approves European Union Public licence

ΕΕΛ/ΛΑΚ - Εταιρεία Ελεύθερου Λογισμικού /Λογισμικού Ανοικτού Κώδικα

2011-02-12T15:57:00.001-08:00

ΕΕΛ/ΛΑΚ - Εταιρεία Ελεύθερου Λογισμικού /Λογισμικού Ανοικτού Κώδικα

ΔΕΛΤΙΟ ΤΥΠΟΥ
Εταιρεία Ελεύθερου Λογισμικού /Λογισμικού Ανοικτού Κώδικα: Δυναμική Προώθηση και Ανάπτυξη του ΕΛ/ΛΑΚ στο χώρο της Εκπαίδευσης, του Δημόσιου Τομέα και των Επιχειρήσεων

Σημαντικοί φορείς και Ανώτατα Εκπαιδευτικά και Τεχνολογικά Ιδρύματα ενώνουν τις δυνάμεις τους και δραστηριοποιούνται για την επέκταση της χρήσης των εφαρμογών του ΕΛ/ΛΑΚ στη χώρα μας: ιδρύουν την «Εταιρεία Ελεύθερου Λογισμικού /Λογισμικού Ανοικτού Κώδικα» (ΕΕΛ/ΛΑΚ). Η ΕΕΛ/ΛΑΚ, εταιρεία με μη κερδοσκοπικό χαρακτήρα, έχει ως κύριο στόχο να συμβάλλει στην προώθηση και ανάπτυξη του ΕΛ/ΛΑΚ στο χώρο της εκπαίδευσης, του δημόσιου τομέα και των Επιχειρήσεων στην Ελλάδα.

Η εταιρία ΕΕΛ/ΛΑΚ ανταποκρινόμενη στο αυξανόμενο ενδιαφέρον για τα οφέλη της χρήσης του Ελεύθερου Λογισμικού, θα αποτελέσει κέντρο γνώσης και πλατφόρμα διαλόγου για το Ελεύθερο Λογισμικό/Λογισμικό Ανοικτού Κώδικα, και θα αναλάβει πρωτοβουλίες που θα διευκολύνουν και θα επιταχύνουν την διείσδυση του στους παραπάνω τομείς:
• θα ευαισθητοποιήσει το κοινό σχετικά με τα οφέλη που προκύπτουν από την υιοθέτηση και ανάπτυξη του ΕΛ/ΛΑΚ.
• θα φροντίσει για την έγκυρη και έγκαιρη πληροφόρηση σε θέματα που αφορούν το ΕΛ/ΛΑΚ στην Ελλάδα και το διεθνή χώρο (πχ. κωδικοποίηση βέλτιστων πρακτικών, συγκέντρωση και επεξεργασία στοιχείων για την εξέλιξη ποσοτικών και στατιστικών δεικτών, του θεσμικού και νομικού πλαισίου, του διαθέσιμου λογισμικού και εφαρμογών)
• θα εργαστεί ώστε να υπάρξει συνεργασία για την ισότιμη συμμετοχή όλων των άλλων φορέων που έχουν άμεσο ή έμμεσο ρόλο στη διάδοση και ανάπτυξη του ΕΛ/ΛΑΚ στην Ελλάδα, όπως μεταξύ άλλων της κοινότητας προγραμματιστών ΕΛ/ΛΑΚ στην Ελλάδα καθώς και όσων ενδιαφέρονται να αναπτύξουν επιχειρηματική δραστηριότητα που σχετίζεται με το ΕΛ/ΛΑΚ
• θα δημιουργήσει κέντρο παρακολούθησης (monitoring) για το ΕΛ/ΛΑΚ στην Ελλάδα (καταγραφή δράσεων και έργων, καταγραφή διαθέσιμου λογισμικού και εφαρμογών, καταγραφή αναγκών για την εισαγωγή και χρήση του σε διαφορετικούς τομείς, αναγνώριση προβλημάτων στην εισαγωγή/χρήση,
στατιστικά στοιχεία και δείκτες, εξέλιξη θεσμικού και κανονιστικού πλαισίου, βιβλιογραφία, φορείς και οργανώσεις που αφορούν το ΕΛ/ΛΑΚ στην Ελλάδα)
• θα συμβάλει στο συντονισμό των ομάδων εθελοντών προγραμματιστών ΕΛ/ΛΑΚ στην Ελλάδα, ώστε να αποτελέσουν τον βασικό κορμό για την ανάπτυξη και υλοποίηση λογισμικού και εφαρμογών
• θα υποστηρίξει την ανάπτυξη και προώθηση επιχειρηματικών μοντέλων που βασίζονται στο ΕΛ/ΛΑΚ, καθώς και την ενημέρωση των επιχειρήσεων για τηνυιοθέτηση τους ή για τη μετάβαση τους σε αυτά
• θα προσφέρει τεχνική υποστήριξη εφαρμογών ΕΛ/ΛΑΚ και συγκεκριμένα:
δημιουργία υπηρεσίας υποστήριξης (help-desk) για χρήστες και ομάδες ΕΛ/ΛΑΚ, μέριμνα για εξελληνισμό (εντοπιοποίηση) λογισμικού, ανάπτυξη γλωσσάριου, επικουρική ανάπτυξη εφαρμογών για τις οποίες υπάρχει ζήτηση
στην Ελλάδα.Η υλοποίηση όλων των παραπάνω στόχων βασίζεται στην ενεργή συνεργασία
• της ελληνικής κοινότητας χρηστών και δημιουργών εφαρμογών (developers) ΕΛ/ΛΑΚ,
• των εργαστηρίων ΑΕΙ, ΑΤΕΙ και Ερευνητικών Κέντρων της Χώρας που χρησιμοποιούν και αναπτύσσουν ελεύθερο λογισμικό,
• των ενδιαφερόμενων φορέων-χρηστών (δημόσιοι φορείς, εκπαιδευτικοί φορείς και επιχειρήσεις),
• των εταιρειών που δραστηριοποιούνται στους τομείς των τεχνολογιών πληροφορικής και επικοινωνιών που θα οδηγήσουν στη δημιουργία ικανής βάσης επιχειρησιακών μοντέλων υπηρεσιών ανάπτυξης και υποστήριξης ΕΛ/ΛΑΚ.
Φορείς που συμμετέχουν:
Το Εθνικό Δίκτυο Έρευνας και Τεχνολογίας (ΕΔΕΤ Α.Ε), το Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών(ΕΚΠΑ), το Ερευνητικό Κέντρο «Αθηνά», το Εθνικό Κέντρο Τεκμηρίωσης (Ε.Κ.Τ.), το Εθνικό Μετσόβιο Πολυτεχνείο (Ε.Μ.Π.), το Ερευνητικό Πανεπιστημιακό Ινστιτούτο Συστημάτων Επικοινωνιών και
Υπολογιστών (Ε.Π.Ι.Σ.Ε.Υ.), το Ακαδημαϊκό Δίκτυο «GUNET», το Οικονομικό Πανεπιστήμιο Αθηνών (Ο.Π.Α.), η Ελληνική Εταιρεία Επιστημόνων & Επαγγελματιών Πληροφορικής & Επικοινωνιών (Ε.Π.Υ.), το ΕΚΕΦΕ «Δημόκριτος», το Τεχνολογικό Εκπαιδευτικό Ίδρυμα Αθήνας (Α.Τ.Ε.Ι. ΑΘΗΝΑΣ), τo Πανεπιστήμιο
Αιγαίου, το Πανεπιστήμιο Μακεδονίας (Π.Μ.), το Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης (Α.Π.Θ.), το Ανώτατο Τεχνολογικό Εκπαιδευτικό Ίδρυμα Καβάλας (Α.Τ.Ε.Ι. ΚΑΒΑΛΑΣ), το Τεχνολογικό Εκπαιδευτικό Ίδρυμα Λάρισας (Α.Τ.Ε.Ι. ΛΑΡΙΣΑΣ), το Πανεπιστήμιο Πατρών (Π.Π.), το Ερευνητικό Ακαδημαϊκό Ινστιτούτο Τεχνολογίας Υπολογιστών (Ε.Α.I.T.Y.), το Πανεπιστήμιο Πελοποννήσου, το Ανώτατο Τεχνολογικό Εκπαιδευτικό Ίδρυμα Καλαμάτας (Α.Τ.Ε.Ι. ΚΑΛΑΜΑΤΑΣ), το Πανεπιστήμιο Κρήτης (Π.Κ) και το Πολυτεχνείο Κρήτης.

Το Διοικητικό Συμβούλιο της ΕΕΛ/ΛΑΚ
κ. Θεόδωρος Καρούνος, Εκπρόσωπος ΕΜΠ, Πρόεδρος
κ. Νεκτάριος Κοζύρης, Εκπρόσωπος ΕΔΕΤ ΑΕ, Αντιπρόεδρος
κ. Αλέξιος Ζάβρας, Στέλεχος της κοινότητας ΕΛ/ΛΑΚ
κ. Κωνσταντίνος Μαργαρίτης, Εκπρόσωπος Πανεπιστημίου Μακεδονίας
κ. Χρήστος Μπούρας, Εκπρόσωπος Πανεπιστημίου Πατρών
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DEVOXX 09

2009-11-17T11:11:00.000-08:00

Two whole years have passed, since Javapolis 2007. I decided to attend Javapolis, now called Devoxx, again, with the same excitement as before. And since a (female) Java developer friend complained that I didn't update my blog about it, I decided to do so.

Even in the middle of the financial crisis, something like 2500 people attended this year's event, which took place from 16th-20th of November. The kiosks where less and less rich than from what I remember two years ago. However, the excitement was still the same, maybe higher!
Only one other Greek guy came for the whole event, Paris Apostolopoulos, the founder of JHUG. Dimitris Andreadis, now project manager or something at jboss, joined in the 3rd day. So, only 3 Greek guys this time, very few compared to the around 7 that were back in 2007.

Well, let's get started. I focus mainly on technology in this blog, putting down what I managed to note during the presentations. You may find the conference schedule in http://devoxx.be/display/DV09/Schedule.

Day 1 - University Day 1

Unfortunately, I didn't keep many notes the first day. I started with Introduction to Java Generics by Prof. Eric Steegmans of university of Leuven. Well, I had some questions about generics, which I hoped this session would help to clarify, which it did. Even though it was introductory in nature, it turned out to be quite fruitful. I put down few notes:

Since, due to backwards compatibility, every generic type is translated to an Object, and since we cannot instantiate a generic type, it makes sense to write something like: this.elements = (E[]) new Object[Math.abs(capacity)];
We can always attempt to return a wrong type

T t = (T) new Date();
T f() {return (T) new Date(); }

Eric also demonstrated how we can use Generics to create whole frameworks, and he demonstrated an implementation of the Composite pattern using Generics.

After lunch, I attended JSF 2: Keep the progress coming by Dan Allen, Peter Muir and Andy Schwartz . A lot of new features where presented, but unfortunately I didn't keep many notes. I remember however one useful feature:
javax.faces.VALIDATE_EMPTY_FIELDS = true

in the web.xml which checks for empty fields. You may start a jcp.org account and of course check javaserverfaces.org for JSF2.next.

I then attended Easing JPA data access with Hades by Oliver Gierke , which has some useful additions. Please check the http://hades.synyx.org web site.

Finally, Spock - the smarter testing and specification framework by Peter Niederwieser is a testing framework based on Groovy, that has a common syntax to run both junits and mock objects. The Next Generation Profiling and Diagnostics Tools by Noora Peura and Anders Astrand has been JRockit. This is actually a JVM which allows you to profile your application.

Day 2 - University Day 2

The kiosks and stands were in place. Around for collecting any goodies like pens, T-shirts etc. Less participants than other times. A good collection of books at Amazon prices.
The second day started with the presentation of The Java EE 6 Platform by Antonio Goncalves and Alexis Moussine-Pouchkine. These two amazing guys presented all the new specification that will be part of JEE 6:

JPA 2.0: pessimistic locking, caching, Criteria API as an alternative to SQL queries and JPQL and type safety
Servlet 3.0: plugability, asynchronous support, FileUpload (finally!!!), no need for web.xml (@WebServlet annotation); it will be supported by Glassfish 3, Tomcat 7, JBoss 6, Jetty 8
Managed Beans 1.0, EJB 3.1 & 3.1 lite: Everything is managed beans. E.g. EJB is a managed bean with transactional support, security and multithreading; RESTful service is a managed bean with HTTP support. EJB lite allows EJBs to be deployed to .war files (no need for .ear files). EJB 3.1 lite spec contains local session beans, security, interceptors, CMT/BMT and injection; but not CMP, MDBs, JMS, RMI/IIOP etc. It also adds an embeddable EJB container (e.g. for testing), Singleton components with concurrency management per application per JVM, optional remote interfaces, asynchronous calls (no threads allowed) etc.
JAX-RS 1.1 adds support for RESTful web services and integrates with EJBs. Simply annotate a stateless EJB with (some of) the following annotations to make it a service (everything is transactional): @Path("/path") @GET @Produces("text/html") @POST @Consumes("text/xml").
JSF 2.0 does not require Servlet 3.0. Facelets has become the alternative to JSPs View Description Language or VDL. faces-config.xml is also optional (like web.xml); navigation now belongs to the page, e.g. return "targetPage.xhtml"; Component creation is easy; single .xhtml files with JSF tags and no Java code. Error reporting and stack trace has been improved and looks like ASPX .NET's. For the first time there is official Javascript support via jsf.js; e.g. jsf.ajax.request and f:ajax tags. Other features introduced are new scopes, templates (layouts), project stages (e.g. dev, test, production) etc.
Bean Validation 1.0 introduces the rule constraint once, validate anywhere. Declarative validation is done with the annotations @NotNull @Valid @Size etc.
Profiles to simplify the spec; currently, only one profile, Web Profile is supported (no EJBs, no JMS etc.)
Standard (portable) JNDI names across application servers
Interceptors 1.1 now separated from EJB spec
@Inject tag for dependency injection
JCDI 1.0 which allows developers to bind Java EE components to lifecycle contexts, to inject these components, and to enable them to support loosely coupled communication

Recommended book: "Beginning Java™ EE 6 Platform with GlassFish™ 3: From Novice to Professional" of Antonio Goncalves.

From the server side to the client side, The JavaFX Platform - A Java Developer's Guide by Stephen Chin. JavaFX is the new way for building rich clients, or GUIs. It is a replacement (?) of Swing. It is the future, as Sun claims.
Example code:
Stage {
scene: Scene {
content: []
}
}
Stage is the equivalent to Swing's Window/JFrame. Inspired from 3D graphics I suppose, you then define a scene, which represents the scene graph of the components to be added, and then the content where you add the components. scene:Scene <=> Scene scene = new Scene();
JavaFX has support for closures, new layouts (HBox, VBox, Tile, MigLayout etc.), binds (the equivalent to Swing events), sequences, animations (e.g transitions) and type inferencing. It doesn't support annotations, generics and multi threads. It is a strongly typed language like Java. Examples of:

binds (regular/lazy): var x = bind a + b; whenever a or b change, x changes as well
sequences: [1 .. 3] means 1 2 3
[1 .. <4] means 1 2 3
[1..3 step 2] means 1 3
var ints = [1 4 4 6 5]
ints [k | k>4] returns 6 5
insert -1 into ints[2]
delete 4 from ints returns [1 6 5]
Support for stylesheets (.css)

Try JfxBuilder and FxBuilder.

JavaFX for Mobile applications currently supports only the common profile and runs on Windows ME platforms.

Recommended book: "Pro JavaFX Platform" by James Weaver et al.
Recommended sites: http://javafx.com, http://jfxtras.org, http://learnjavafx.typepad.com, http://steveonjava.com

A Year of Monitoring with Java-monitor by Kees Jan Koster got us into the workings of the garbage collector, or garbage collectors. In case you didn't know, there are two garbage collectors in Java: the Scavenger who is faster but doesn't do such a good job, and the MarkSweeper who is slower, but cleans everything! He gave examples of memory leaks, like e.g. how file descriptors in Linux (1024) can easily been allocated (FreeBSD has some 10000 fds, Solaris?), so man ulimit and limits commands to see how to increase the number of file descriptors in your system.
-Xss limits thread stacks. Don't use System.gc() inside an application server e.g. Tomcat; it affects all deployed applications. Use the server version of jdk, i.e. java -server.

Recommended sites: http://www.java-monitor.com

In Scala Actors: A Tool to Harness the Power of Multicore CPUs on the JVM, Frank Sommers presented Scala actors who communicate via immutable messages. Actors are executed in threads in a thread pool. You can write your own actor by extending scala.actors.Actor. Messages are defined with case classes. The framework allows pattern matching and remote actors.

Recommended book: "Programming in Scala" by Martin Odersky, Lex Spoon, and Bill Venners
Recommended site: http://www.artima.com

Day 3 - Conference Day 1

Devoxx's first conference day started with lots and lots of people, joining just for the conference. And with the traditional key note of the guy who started all this, Stephan Janssen. He was happy that participants reached once again 2500. The presentations will be available for free in parleys.com from January 2010.

Steven Harris from Oracle talked about Java, the Platform for the Future. He spoke about WebLogic's Dynamic module which uses profiles to capture collections of OSGi bundles and about virtualisation. He created a VMWare instance, by using Oracle Assembly Builder Studio, that ran just a java application.

The next key speakers Roberto Chinnici and Ludovic Champenois presented Java EE 6 and GlassFish V3: Evolution of a Platform. The good news are that Java EE 6 together with Glassfish v3 and Netbeans 6.8 will all be released on 10th December 2009! I already spoke about the new features of the new JEE 6 platforms above, but here some additional things:

@Email String email;
Modular web applications
EJB Container now works in Java SE too
@Singleton, @Startup beans, @asynchronous invocations
JSF 2.0 features: standardized facelets, composite components, autodiscovery of components, javascript API (jsf.js) for AJAX support
A POJO is turned into an EJB 3.1 by adding the @Stateless annotation to it.

Then Christophe Coenraets from Adobe took over with his impressive Integrating designers into your application development presentation. Adobe Flash 10.1 targets smartphones and flash applications now run exactly the same in the smartphone as in the desktop. AIR 2.0 now allows accessing native applications. Finally, he gave an impressive presentation of Adobe Flash Catalyst, a tool which allows a developer to transform a .psp image created by the web designer to the GUI of a web application!

After the lunch break, I chose to attend JDK7 Update by Mark Reinhold. Mark showed what we should expect from JDK 7. JDK 7 will be modular, multi-lingual (Java, JRuby, Jython etc.), productive and performant. As the size of the JRE is around 13 Mb, Java is currently refactored into modules; there will be a base module and other modules which will depend on this base module, like awt module, swing, sound, tools, corba etc. modules. Modules may eventually replace jar files. The user will download just the modules s/he needs.
JDK 7 introduces the diamond (<>) operator: Map<String, String> map = new HashMap<>();
Some other new syntax has been inspired from Ruby, e.g.: long l = 322_123_888L; New binary representation: 0b1001. The [] operator is not privileged by arrays only:
List<String> list = ["1","4","5"];
list[2] = "6";

JDK 7 will have limited closure support and additional multi-threading goodies (invokeAll). Static methods can be declared in interfaces. An example of a closure:
#int (int, int) multiplier = #(int x, int y) { x*y }

Recommended site: http://openjdk.java.net/project/jdk7.

After the lunch break, I decided not to attend James Gosling's talk, but HTML 5 Communications - The New Network Framework for the Web by Frank Greco instead and it proved to be a rewarding choice! HTML 5 will bring Web 3.0 in our lives. Web 1.0 served only static pages; Web 2.0 is dynamic, with the advances of Ajax and RIA applications; Web 3.0, however, will be a Read/Write Web, event-driven, secure, reliable and will support real-time communications with no latency.

W3C and IETF, who work together on HTML 5, have decided to get rid of HTTP altogether; HTTP is half-duplex protocol. A new protocol WS (and its equivalent WSS, i.e. secure) will be introduced in Web 3.0, where WS stands for Web Sockets, i.e. we will be able to write ws://www.foo.com!

The new spec will contain the following:

TCP bi-directional Web Sockets
Standardised HTTP Streaming which means that browsers will support mashups (this is a standardisation of Comet for server sent events)
Secure cross-site remote connectivity
Secure browser cross-document messaging

The Web Sockets API is already available for download and Frank presented a demo of real-time stock option available by Kaazing. In short, Web 3.0 will be:

highly scalable
backwards compliant
extensible with new protocols, security etc.
performant, and
compliant with open standards

jBPM is a framework I always wanted to use, but never had a chance. So, whenever I find the opportunity, I try to go and listen to what Tom Baeyens has to say about it. jBPM4 in Action is a total refactoring of the previous version.

Business Process is defined as a way of doing things with a certain goal. jBPM has a transactional state machine, a generic graph execution engine and a process VM. In version 4 there is:

new API with new query mechanism
native spring integration
compact DB schema
GWT web console
Signavio web modelling
BPMN2 jPDL (process language) that supports concurrency and asynchronous continuations
task forms for rapid prototyping
eclipse plugin (eclipse process designer)

Recommended sites: http://www.jbpm.org, http://www.jorambarrez.be

Being curious of Comet, I decided to go for Writing Asynchronous Web application (Comet) using the Atmosphere Framework by Jean-Francois Arcand and Paul Sandoz.
The guys compared polling, Ajax push and HTTP streaming. Atmosphere is based on RESTful web services, i.e. with JAX-RS. No vendor lock, works with all application servers, runs on top of any Servlet 2.3/3.0 compliant servlet container. REST + Jersey = Atmosphere plus a number of tags: @Suspend, @Resume, @Broadcast, @Schedule, @Cluster. Features:

cookie based transactions
web socket support
persistence support
adaptive event aggregator

Recommended sites: http://atmosphere.dev.java.net, http://jersey.dev.java.net

The day finished with Project Coin by Joseph D. Darcy and the new additions to Java 7. So, there will be the possibility to write:

String s;
switch (s) {
case "one" :
...
}

variable names will contain any character
automatic resource management, e.g.

try (FileInputStream is, FileOutputStream os) {
...
}

i.e. there will be no catch statement and resources will be released automatically.

simplified varargs method invocation
collections will now use [], e.g.

List l = new LinkedList<>();
l[0] = 6;

New elvis operator (from Groovy): a ?: b <=> if (a!=null) a else b
JSR 292 support
EnumSet, EnumMap
reification
multiple exceptions support

try {
...
} catch (final Exception1 ex | Exception2 ex) {
throw ex;
}

The day finishes with a beer call and free chips.

Day 4 - Conference Day 2

Day 4 starts very interestingly too, with Ivar Jacobson and Do we really know how to develop software? For those who didn't know, Ivar is one of the three amigos behind UML.

Ivar spoke about people who don't know about software and try to make money out of it. He also addressed the issue that academic research must be aligned with industry practice.

There are currently thousands of methods and methodologies which simply reinvent the wheel over and over again. We don't know what others are doing. We need a theoretical basis to develop software!!! One that aligns academic research with industry practice.
He has started a Software Engineering Method And Theory (SEMAT) which can be found in http://www.semat.org. In this work, he defines a kernel to be an empty process which defines a common basis to start with. The kernel ensures common understanding across all teams. The kernel is surrounded by practices which define the various practices specific to the kernel.
He asks to give him our thoughts about this theory by sending an email to a_theory@ivarjacobson.com. He doesn't know if he will succeed or not, but he finished his presentation with a saying of Kurt Lewin: "There is nothing as practical as a good theory".

And the day continues with Robert C. Martin or uncle Bob and Filling The Professionalism Gap: Craftsmanship and Policy. Eccentric uncle Bob, author of books like "UML for Java Programmers" and "Clean Code" starts walking up and down the scene describing the story of his career. He started his career in the late 70s, when at the age of 18 he was hired along with 2 other teenagers to migrate a program to a new system for which they even had to write the operating system for! He went on describing the 80s, the 90s and our decade and he always ended up to the same conclusion between management and developers: "They hated us; we hated them"!!!!! He dared to say a great truth, that we, developers, do not have a defined profession yet! The difference between professionalism and craftmanship is that a professional is proud of what s/he does, and is able to do a good job. What prevents us from doing a good job? The managers? He advises that we should learn to say no! We are being viewed as blue colar workers (with a hourly rate). Do doctors and lawyers charge per hour?
There is also a temptation for developers to become managers (management is a profession by the way).

There is a manifesto of software craftmanship, which came out of the agile manifesto.
So, how can a software developer behave like a professional?

Do no harm (say no when managers say they want it tommorrow)
Write clean code by using TDD with 100% test coverage (it is not professional to not know if your code works)! QA is a specification not a verification.
Work team-based, not project-based and keep the team together! Do not change teams depending on projects; all projects should be assigned to the same team.

Recommended book: "Clean Code" by Robert C. Martin.
Recommended site: http://www.objectmentor.com

After such a morning, I continued with Spring Framework 3.0 by Arjen Poutsma. So, what to expect from the 3rd version of the most used Java framework. Well, six things:

Java 5 syntax
Expression language as an independent component
RESTful web services support
Portlets 2.0 support
Declarative annotation support (JSR 303)
JEE 6 support

In more detail. Spring 3.0 will provide Generics support which will backward compatible like in Java. Object XML (OXM) module moved to the core. There will be property editors, type converters and formatters, and annotated factory methods and meta-annotations.
Spring configuration can now be defined in a Spring Java config class:

@Configuration
public class AppConfig {

}

EL came out of the core as a separate component. EL is now used, additionally to web navigation, in bean definitions, in annotations, and in default context attributes determined at runtime.

Sping 3.0 now supports URI templates to create RESTful URLs, e.g. /hotel/{hotelid}

@PathVariable @RequestMapping(/hotels/{hotelid}
class HotelController {
public void handleHotel(@PathVariable ("hotel") String hotel) { }
}

Other annotations: @CookieValue, @RequestHeader, @RequestBody, @ResponseBody.

template = new RestTemplate();
result = template.getForObject(uri, HotelList.class, "1");
template.postForLocation(uri, booking, vars); // vars is a hashmap of {hotel}
template.delete(location);
template.execute(uri, HttpMethodGET, myReqCallback, myResCallback);

Partial support for JEE 6 will include: JSF 2, JPA 2, Bean Validation, JSR 303 and dependency injection. Spring 3.1 will provide full JEE 6 support.

In Spring 3.0, Common Attributes and TopLink have been pruned. MVC controller hierarchy, JUnit 3.8, Struts 1.x, and some outdated helper classes have been deprecated.

And the day continues with The not so dark art of Performance Tuning by Kirk Pepperdine and Dan Hardiker. Kirk, together with Java evangelist Heinz Kabutz, are located in Chania Crete from where they provide expertise on many Java issues; one of them, performance. Kirk demonstrated Apache JMeter, a tool for load and stress testing, to find performance problems in a web application. One can create a test plan to do his/her tests. There are four dominating consumers: hardware, JVM/OS, application and actors.
He also talked about VisualVM, ThreadDumpAnalyzers and stack traces.

Recommended site: http://www.javaperformancetuning.com

iBeans: dead-simple integration for the Web by Ross Mason. Ross presented an alternative solution to SOA and ESB for web integration. An iBean is a Java Interface with annotated methods; a definition of how to talk to a service; a web service without XML! iBeans provide a simple solution for performing common integration tasks such as receiving and sending messages over Email, JMS or calling a Web Service. iBeans use no SOA, are cross-platform, easy to resuse and task-focused. iBeans central is a shared repository of iBeans. There is a Server API with functions like send/receive data, schedule tasks, create request/receive services, support protocols, and a Client API which allows you application to talk to other systems like Twitter, Google, Amazon, Facebook etc.
iBeans deals with details like security in various service providers.

The Server API is contained in ibeans.war and has a number of useful annotations to use in your server side code:

@Send (uri="xmpp:// ... ")
@Schedule (interval="60000")
void method() { ... }

@Receive (uri="jms://my_queue")
void onMessage(Object msg) { ... }

@Transform // transforms a JMS message to an object we define e.g. Order

@IntegrationBean

On the client side, you can use iBeans in Javascript:

var ibeans = new IBeansClientCJ;
var x = ibeans.config.get( ... );
ibeans.twitter.set(x);

iBeans provide support for GWT, Grails, Spring, Struts 2.x, Play! Its target is to become the WCF for the Web. What's next? WS support.

Recommended site: http://www.mulesoft.org/display/IBEANS/Home

After the lunch break, back to some more JEE stuff: Deep dive on the Java EE 6 platform with GlassFish V3 by Roberto Chinnici and Ludovic Champenois. Lets see what new features does JEE 6 bring on.
- The new Web Servlet container brings initializers. Initializer libraries are stored in /META-INF/resources/. Initializer class implements ServletContainerInitializer inside /META-INF/web-fragment.xml:

<web-fragment>
<servlet>ServletClassName<.servlet>
</web-fragment>

- CDI portable extensions. WebBeans support JSR-330 Context Injection. There is context management with scopes (and a new @ConversationScope), bean discovery and injection points in a bean. Below is an extension interface:

public Interface Bean extends Contextual {
interface AnnotatedType extends Annotated;
}

These are stored in /META-INF/services. Finally, there is support for Before/After discovery events.

Glassfish v3

Very fast, very small, modular, embedded, OSGi, RESTful administration, various containers (JRuby, Django, Grails, Rails). Containers are added/removed automatically.
There is also a stripped jar (<1Mb) that contains all JEE 6 jars.

java -jar glassfish.jar mywebapp.war

There is automatic compilation support; thus you can change your servlet, then save your changes and refresh your browser to see your changes. There is a maven web application to manage your maven projects.
Monitoring and management are exposed via RESTful web services:
http://localhost:4848/management/domain
http://localhost:4848/monitoring/domain/

Recommended site: http://java.sun.com/javaee/downloads/index.jsp

The last presentation of the day was Maven Reloaded by Jason van Zyl. Jason presented the new features of Maven 3.0. There will be backwards compatibility. The project builder has been refactored, there is a pluggable model reader and mixins to extend POMs, DSLs (Groovy, Ruby, Python, Scala), incremental build support (also in mEclipse), lifecycle extension points, OSGi bundles and a maven shell.

And this ends day 4.

Day 5 - Conference Day 3

The companies have started packaging their kiosks, and the exposition area seems empty. After 4 tiring but rewarding days, time for some fun with Gaming JavaFX by Richard Bair and Jasper Potts.
Their games are based in a physics library: Phys2D --> JBox2D --> Phys2D.
World contains a static and dynamic body. Collision detection is expensive. In JavaFx, you start by creating a PhysicalScene which contains a PhysicsWorld with gravity and interactions. A PhysicalObject is a node in the scene with a physics body which has a geometry. Prism replaces AWT, and talks directly to the hardware (Direct3D or OpenGL).
The speakers presented a number of games, one involving explosions. An explosion visual has been emulated with iterating images.

class ExplosionFS extends FourceSource
public var explosions[]

Stage {
Scene: PhysicalScene {
content {
Ground {
...
}
Ball {
}
}
}
}

Recommended site: http://www.fxexperience.com

The next presentation was mainly due to work. Managing Glassfish on OpenSolaris by Simon Ritter. Glassfish and OpenSolaris are both free and open source under CDDL license. Simon talked about various containers: ZFS, Zone (multi-core CPUs virtualisation), Crossbow (network virtualisation), SMF (automate services) and how to run GF with RBAC (Robust Access Control) and SMF.
ZFS is the new file system created by SUN Microsystems. It is a pool based storage with no volumes, that prevents silent data corruption (i.e. no need for fsck) using a big checksum, almost zero overhead and easy rollback.
Volumes have been replaced by a 128-bit storage pool and all free storage is always available, fast and simple. ZFS snapshots are read-only, incremental, thus efficient. ZFS storage pools can be accessed with the following commands:

# zpool list
# zpool status
# pfexec zpool create mypool ()
# pfexec zfs snapshot
# pfexec zfs rollback
# pfexec zfs send
# pfexec zfs receive

Zones virtualise system resources (CPUs, NICs, memory etc) not the hardware. They are lightweight and no virtual machine is needed. Crossbow, e.g. can virtualise a number of NICs (Virtual NICs) that run different applications:

SMF provides a uniform mechanism to manage services:

svcadm [disable|enable] mydomain

Dependencies are declared in an xml manifest for the service. Compared to rc*.d, there is a GUI.

asadmin create-service

And the last presentation was ArchiMate: A common language for Enterprise Architecture by Remco Blom. Archimate is a standard language for modelling and visualising enterprise architectures. It bridges the gap from business pictures to technical UML diagrams. UML is not designed for Enterprise Architecture; business people don't understand it; there is no explicit service paradigm and has many models.
BizzDesign is an IDE that supports the Archimate language. Architype is a structure of a system in terms of components, relations, underlying principles and visible properties. Enterprise Architecture has a process view (way of working) and a product view (design). TOGAF (Open Group Architecture Framework) defines the process and Archimate defines the language. The archimate IO specification defines 3 layers (business, application and technology) and 3 aspects (passive structure, active structure and behaviour).
Then, he demonstrated the bizzdesign tool and he didn't miss to mention a TOGAF eclipse plugin, too. BizzDesign can be integrated with Visio (with stencils) or can be downloaded as an IDE (BizzDesign Architect). One can refer from an archetype diagram to a UML diagram and vice versa.

Recommended sites: http://www.archimate.org, http://www.opengroup.org/archimate, http://bizzdesign.com.

And this ends 2009 Devoxx conference. All the presentations will be available from January next year hopefully, in parleys.com and all those who couldn't participate will have a chance to take a snif of what was presented there, and what you missed. See you, hopefully, next year!

Are analysts/GUI designers doing a good job?

2009-06-14T04:35:00.000-07:00

I happened to ask for a new telephone in the company I work, and I went to the guy who was responsible. The guy complained to me about the new application he had to use, a Java Swing application that allowed him to set the phone number to the UTP plug etc. "In the previous application you could open a new account in just one click. With this new one, you have to save, click here, then back to the tree, wait until it is saved etc." he complained.

I wondered what the analyst/GUI designer responsible for the GUI of that application was thinking. Didn't he look at the previous application s/he was replacing? The new application had to be at least as easy and fast to use as the previous one. Do we keep in mind the one-click pattern of WWW when we design the GUIs of our Swing applications, or not?

Our purpose, as analysts/designers/developers is not only to be able to create nice interfaces with great components (trees, tables etc.) but also to make them as user friendly as possible. Listen to the user next time, and understand his/her needs!

How to remove elements from an array

2009-04-02T06:50:00.002-07:00

Problem

I have an array, e.g.

String strArray[] = new String[3];

and I 'd like to remove elements that satisfy a certain condition.

You could write something like:

List lstStrings = Arrays.asList(strArray);
for (int i=lstStrings.size()-1; i>=0; i--) {
   String s = (String)lstStrings.get(i);
   if (s.equals("target")) {
       lstStrings.remove(i);
   }
}

and you 'll get a

java.lang.UnsupportedOperationException at java.util.AbstractList.remove

What's wrong? Well, the problem lies in this command:

List lstStrings = Arrays.asList(strArray);

The result of Arrays.asList is an Arrays$ArrayList (and not an ArrayList) which is immutable and doesn't provide for a remove method.

Solution

List lstStrings = new ArrayList(Arrays.asList(strArray));

JSPs and mime types

2009-02-27T07:34:00.001-08:00

I have a simple request. I have an .xml file stored somewhere in my server. The file is an Excel sheet saved in .xml format. I simply point to it from an anchor in my jsp page. I want, when the user, left-clicks to it, MS-Excel (or OO Calc) to open to display the file instead of its contents being displayed inside the browser. So, I set the mime type in the anchor tag like so:

<a type="application/vnd.ms-excel; charset=UTF-8" href="<c:url value='/templates/template.xml'/>"><img src="<c:url value='/images/excel.gif'/>"></a>

The trick seems to work fine for Firefox, but alas, not for Internet Explorer. If someone knows a solution, please let me know. :-)

Speed up Intellij IDEA startup time

2009-02-11T00:53:00.000-08:00

Intellij IDEA 8 has become a big IDE and takes quite sometime to startup. Here are a couple of hints to improve startup time:

replace idea.exe.vmoptions contents with the following one:

-Xms400m
-Xmx800m
-XX:MaxPermSize=120m
-ea
-Dsun.awt.keepWorkingSetOnMinimize=true

increasing the RAM size allocation even more if your machine can handle it, e.g. to 1024m

2. modify idea.properties by moving the config directory to a faster drive if e.g. you home profile is saved in a network drive, e.g.:

# idea.config.path=${user.home}/.IntelliJIdea80/config
idea.config.path=D:/Config/.IntelliJIdea80/config

Freelance in Northern Europe vs. in Southern

2009-01-15T02:57:00.000-08:00

Did you know this? If you negotiate your daily rate in Northern Europe and/or US, it is without VAT. If you do in the south, then VAT is included! This is how companies save money!

So, if e.g. your daily rate is 500€, then in northern Europe you invoice the customer 617 € (assuming VAT 19%). In southern Europe, you invoice 500€, and you pay the VAT, hence your actual rate is 405€!!!

2008-12-02T00:20:00.000-08:00

Οι καθηγητές Πληροφορικής αγωνίζονται ενάντια στην απαξίωση - υποβάθμιση του επιπέδου σπουδών Πληροφορικής στο Δημόσιο Σχολείο όπου πρόσφατα μεθόδευσε το ΥΠΕΠΘ και απαιτούν:

Οι αναθέσεις μαθημάτων ΚΑΙ για τα μαθήματα τα σχετικά με την Πληροφορική να γίνονται με βάση το γνωστικό αντικείμενο του πτυχίου και μόνο.
Ο αριθμός μαθητών ανά καθηγητή στα εργαστηριακά μαθήματα να γίνει δώδεκα (12) ΚΑΙ για τα μαθήματα Πληροφορικής και όχι δεκαεπτά (17) όπως τώρα κατ’ εξαίρεση ορίζει η νέα εγκύκλιος.
Ισονομία για τους υπεύθυνους εργαστηρίων Πληροφορικής με τρίωρη μείωση ωραρίου ΚΑΙ για το ΣΕΚ.

ΒΟΗΘΕΙΣΤΕ ΣΤΟΝ ΑΓΩΝΑ ΤΩΝ ΠΛΗΡΟΦΟΡΙΚΩΝ ΓΙΑ ΤΗΝ ΕΚΠΑΙΔΕΥΣΗ ΠΛΗΡΟΦΟΡΙΚΗΣ ΚΑΙ ΜΕΤΑΔΩΣΤΕ ΤΟ ΜΥΝΗΜΑ. Διαβάστε το αυτονόητο.

Tips and tricks

2008-09-29T01:59:00.000-07:00

Tricks on immutability

a. Always make a copy of mutable objects inside your methods, e.g.


void myMethod(Date date) {
 Date myCopy = new Date(date.getTime());
}

b. How do I create an immutable Java Bean or POJO? Make it read-only, and pass any parameters during initialisation (in the constructor):


public class MyClass {
private int param1;
private String param2;
private Date date;

public MyClass (int param1, String param2, Date d) {
    this.param1 = param1;
    this.param2 = param2;
    this.date = new Date(d.getTime());
}

public int getParam1() {
    return param1;
}

public String getParam2() {
    return param2;
}

public Date getDate() {
    return new Date(date.getTime());
}
}

c. Immutable objects and Hibernate

set the access type to “field” in order to use reflection to set the fields instead of property access, which uses setters.
set mutable to false (Hibernate will perform small optimizations, too).

Compare and sort Greek Strings

2008-09-07T04:04:00.000-07:00

Inspired from the article Compare and sort Strings, I hereby present an example of Collators and Comparators with Strings that contain Greek letters.


import java.text.Collator;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Locale;

public class GreekCollator {
private static final Locale GREEK_LOCALE = new Locale("el", "GR");
private static final int NO_COLLATOR = -1;

 private enum CollatorEnum {
  NoCollator(NO_COLLATOR),
  Primary(Collator.PRIMARY),
  Secondary(Collator.SECONDARY),
  Tertiary(Collator.TERTIARY),
  Identical(Collator.IDENTICAL);
  
  private int collatorStrength;
  CollatorEnum(int collatorStrength) {
   this.collatorStrength = collatorStrength;
  }
 }

/**
* @param args
*/
public static void main(String[] args) {
 List<String> words = Arrays.asList("άλλος", "αλάνι", "βασικός", "ελεύθερος", "Ελεύθερος", "Άλλος", "Αλάνι");

System.out.println(words + " - Original Data\n");
  sort(words, CollatorEnum.NoCollator); // don't use a collator
  sort(words, CollatorEnum.Primary);
  sort(words, CollatorEnum.Secondary);
  sort(words, CollatorEnum.Tertiary);
  sort(words, CollatorEnum.Identical);

  System.out.println();
  compare("αβγ", "ΆΒΓ", CollatorEnum.NoCollator);
  compare("αβγ", "ΆΒΓ", CollatorEnum.Primary);
  compare("αβγ", "ΆΒΓ", CollatorEnum.Secondary);
  compare("αβγ", "ΆΒΓ", CollatorEnum.Tertiary);
  compare("αβγ", "ΆΒΓ", CollatorEnum.Identical);

  System.out.println();
  compare("αβγ", "ΑΒΓ", CollatorEnum.NoCollator);
  compare("αβγ", "ΑΒΓ", CollatorEnum.Primary);
  compare("αβγ", "ΑΒΓ", CollatorEnum.Secondary);
  compare("αβγ", "ΑΒΓ", CollatorEnum.Tertiary);
  compare("αβγ", "ΆΒΓ", CollatorEnum.Identical);
}

private static void sort(List<String> aWords, CollatorEnum collatorEnum) {
  if (collatorEnum.collatorStrength < 0) {
   Collections.sort(aWords);
  } else {
   Collator collator = Collator.getInstance(GREEK_LOCALE);
   collator.setStrength(collatorEnum.collatorStrength);
   Collections.sort(aWords, collator);
  }
  System.out.println(aWords.toString() + " " + collatorEnum);
  }

  private static void compare(String aThis, String aThat, CollatorEnum collatorEnum) {
 int comparison = 999;
  if (collatorEnum.collatorStrength < 0) {
   comparison = aThis.compareTo(aThat);
  } else {
   Collator collator = Collator.getInstance(GREEK_LOCALE);
   collator.setStrength(collatorEnum.collatorStrength);
   comparison = collator.compare(aThis, aThat);
  }
  if (comparison == 0) {
   System.out.println("Collator sees them as the same : " + aThis
     + ", " + aThat + " - " + collatorEnum);
  } else {
   System.out.println("Collator sees them as DIFFERENT  : " + aThis
     + ", " + aThat + " - " + collatorEnum);
  }
}

}

Here is the output of the program, for your comments.


[άλλος, αλάνι, βασικός, ελεύθερος, Ελεύθερος, Άλλος, Αλάνι] - Original Data

[Άλλος, Αλάνι, Ελεύθερος, άλλος, αλάνι, βασικός, ελεύθερος] NoCollator
[Αλάνι, αλάνι, Άλλος, άλλος, βασικός, Ελεύθερος, ελεύθερος] Primary
[Αλάνι, αλάνι, Άλλος, άλλος, βασικός, Ελεύθερος, ελεύθερος] Secondary
[αλάνι, Αλάνι, άλλος, Άλλος, βασικός, ελεύθερος, Ελεύθερος] Tertiary
[αλάνι, Αλάνι, άλλος, Άλλος, βασικός, ελεύθερος, Ελεύθερος] Identical

Collator sees them as DIFFERENT  : αβγ, ΆΒΓ - NoCollator
Collator sees them as the same : αβγ, ΆΒΓ - Primary
Collator sees them as DIFFERENT  : αβγ, ΆΒΓ - Secondary
Collator sees them as DIFFERENT  : αβγ, ΆΒΓ - Tertiary
Collator sees them as DIFFERENT  : αβγ, ΆΒΓ - Identical

Collator sees them as DIFFERENT  : αβγ, ΑΒΓ - NoCollator
Collator sees them as the same : αβγ, ΑΒΓ - Primary
Collator sees them as the same : αβγ, ΑΒΓ - Secondary
Collator sees them as DIFFERENT  : αβγ, ΑΒΓ - Tertiary
Collator sees them as DIFFERENT  : αβγ, ΆΒΓ - Identical

References

Java Practices, Compare and sort Strings.

Collections.copy

2008-07-16T00:50:00.000-07:00

Well, it looks like this method contains a "bug"?!?!?

Simply do this test:

public void testCollectionsCopy () {
ArrayList list1 = new ArrayList(3);
list1.add("one");
list1.add("two");
list1.add("three");
ArrayList list2 = new ArrayList(3);
Collections.copy(list2, list1); // throws IndexOutOfBoundsException!!!!!
}

Well, the solution? Pass the collection to be copied as a parameter to the constructor.

ArrayList list1 = new ArrayList(list1);

JavaOne Afterglow 2008

2008-06-28T03:31:00.000-07:00

On Friday, 27th of June 2008, I attended the JavaOne Afterglow 2008 in De Montil, Affligem, a few km outside Brussels. It was a well organised day event, that gave us useful information about the things to come, a summary of what was presented in JavaOne conference. Here is the agenda:

Agenda:
09:15 - 09:45 Registration
09:45 - 10:45 "JavaOne Afterglow keynote"
David Delabassée - Sun Microsystems Belgium
10:45 - 11:30 "Modularity in Java : OSGi and/or JSR 277 ?"
Stijn Van Den Enden - ACA IT-Solutions
11:30 - 12:30 "Project Fuji, an Integration Profile"
Andreas Egloff - Sun Microsystems Inc.
12:30 - 13:30 Lunch
13:30 - 14:30 "Java EE 6"
Alexis Moussine - Pouchkine - Sun Microsystems Inc.
14:30 - 15:30 "Boldly Go Where the Java Programming Language Has Never Gone Before"
Geert Bevin - Terracotta
15:30 - 15:45 Coffee break
15:45 - 16:15 "JavaFX overview"
Jo Voordeckers - RealDolmen
16:15 - 17:00 "Parleys.com: A Flex/AIR, JavaFX and GWT Case Study"
Stephan Janssen - RealDolmen
17:00 - 17:15 Wrap-up and prize raffle

The conference started with David Delabasée, the Java ambassador in Belgium-Luxembourgh, who gave an overview of the new things we are to expect regarding Java 7 as well as other Java technologies such as Java Card. A Java Card is a smart card that contains an application server in it! Hence, you can upload a servlet to itconnect it to various devices and call it from various programs and devices as David demonstrated. David also shown a roadmap of Java through expected version 7, mentioning OpenJDK/IcedTea project, the new Nimbus look & feel in JDK 6 update 10 (consumer JRE). The "Java Virutal Machine" becomes simply "Virtual Machine", as it now hosts not only Java but a large number of other languages such as Ruby, Groovy, Grails, Pascal etc. Characteristics of the new JDK 7 are:

hosting of many languages, as already mentioned
Profiles
JMX 2.0
Visual JVM (a nice tool that will graphically displays the internal of the VM); and
closures

Next, Stijn Van Den Enden, spoke about modularity and compared the current two frameworks, OSGi and JSR 277. As you already know, currently modularity in Java is addressed by packages and interfaces and there is no versioning or access control. If a class in one package needs to access a class in another package, the only way is to declare the class in the other package public, hoping that no one will find out that an internal class is exposed as public.
OSGi solves these problems with bundles. A bundle is a package with some useful metadata about the package in MANIFEST.MF. It separates private from public resources; determines package resolution; and allows versioning.
JSR 277, or Java Module System, is a new specification that addresses the same problem. The equivalent to OSGi bundle is called Java Module and it is packaged as a special kind of JAR, called JAM (JAva Module). Metadata is not in the manifest file, but as annotations.

Andreas Engloff gave a presentation about project Fuji, an integration profile project or standard plugin model for modules. It has three layers, Modularity, Service Orientation and application interface. It is based on OSGi, Open ESB and provides for Enterprise Integration. Andreas presented a demo of the simple workflow language one can use to easily get RSS feeds, filter them by JRuby and feed them to an XMPP (instant messaging) application. He wrote less than 10 lines of simple commands to accomplish this!

The session continued after the lunch break with Geert Bevin from Terracotta who presented 4 hot Java technologies:

Terracotta, an open source clustering framework which allows you to run your code to multiple JVMs seamlessly
RIFE, a full-stack component framework for web applications, which with the principle of continuation, allows you to stop, save and reload a web app state like one does with computer games
Google Web Toolkit; and
Google Android

Alexis Moussine-Pouchkine gave a presentation about upcoming Glassfish v.3 application server as well as about the new features of Java EE 6:

Extensibility
Profiles
Pruning; and
ease of development

After the coffee break, Jo Voordeckers gave a short presentation about JavaFX, or the return of the applet. JavaFX is the new scripting language provided by SUN, that hopes to boost and simplify both desktop and web development. The new "Java 6 update N" is less than 3 Mb, compared to ~12 Mb of current JRE 6, which can be quickly downloaded by clients' machines. However, JavaFX has a number of competitors, like Adobe Flex, MS Silverlight but also JRuby and others.

The conference ended with Stephan Janssens' presentation of parleys.com, and a comparison of 3 hot competitors in the RIA arena, namely, Adobe Flex, JavaFX and GWT.
Adobe provides AIR for desktop and Flex for Web applications; JavaFX is for both the desktop and the web; while GWT is only for developing Web applications. A thing to note is that Flex is only compatible with Flash version 9 or later, so he is developing a version of parleys.com with GWT which is compatible with Flash version 8 for clients that run this version of Flash.

The conference finished with some draws, and the winners won books and a playstation 3.

A well organised conference as I said, but in the middle of nowhere, with no public transport available, and difficult to go there if you don't have a car! :-)

Hashtable vs. HashMap

2008-06-24T01:56:00.000-07:00

HashMaps accept null values, while Hashtables don't.


import java.util.HashMap;
import java.util.Hashtable;

import junit.framework.TestCase;

public class HashMapTest extends TestCase {
   private HashMap map = new HashMap();
   private Hashtable hashtable = new Hashtable();
  
   public void testHashMap() {
       map.put("name", null);
       assertNotNull(map);
       assertEquals(1,map.size());
   }
  
   public void testHashtable() {
       hashtable.put("name", null);
       assertNotNull(hashtable);
       assertEquals(1,hashtable.size());
   }   
}

The 2nd test simply throws a NullPointerException.

Hashtable is historical, according to JavaPractices.

How to debug your web application in JBoss with Eclipse

2008-02-01T00:17:00.000-08:00

For many developers, debugging a web application simply means looking at the logs and trying to figure out what went wrong. Fortunately, there is an easier way. You can debug a web/JEE application the same way you debug a JSE or JME application.
With today's IDEs you can also debug web/jee applications step by step, while the application is deployed to an application server like JBoss. The following trick works with JBoss application server, please contribute for other application servers.
OK, here is the trick. Open %JBOSS_HOME%/bin/run.bat (Windows) or $JBOSS_HOME/bin/run.sh (Linux) and uncomment the line that contains the port 8787, i.e. this line (by simply deleting the rem word in front):

rem set JAVA_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=y %JAVA_OPTS%

If you cannot find the line in run.sh, try $JBOSS_HOME/bin/run.conf.

In your eclipse environment, click on the arrow next to the Debug button and select Debug... Select Remote Java Application and press the New button to create a new configuration of this type.
In the Connect tab, browse your web / jee eclipse project, leave the connection type to Standard (Socket Attach) and enter the host name (localhost if it is local) but modify the port to 8787 (this is JBoss' debugging port). In the Source tab you may wish to add any dependent projects. Click on Apply. That's it.

Now all you need to do is start your JBoss application server, deploy before or after your war or ear file. The application server stops waiting for someone to listen to port 8787. Click on Debug or select the above configuration in the Debug window, and voila, JBoss continues starting up.

Set your breakpoints etc. enjoy!

P.S. Netbeans has very good debugging integration with most of the application servers. If your application server is not listed in its list of available application servers, simply define it under Tools --> Server.

References

Monitoring a remote JBoss Server from Eclipse

Javapolis 2007

2007-12-17T00:17:00.000-08:00

This was my first time in a Javapolis event. Javapolis, like JavaOne, is a fiest of Java. It is not only the new knowledge that one acquires from the various presentations, which are going to be available from parleys.com anyway, but also the exhibition, exchanging ideas with other Java developers, meeting famous authors etc.

This event was even more special because the legend, James Gosling himself, was there! 3000+ participants watched his speech live! Javapolis takes place in Antwerp, Belgium, every year since 2004. It is equal, or even better as some say, from JavaOne, in the US. I really had very good time all these five days, from 10^th to 14^th of December.

Here is my point of view of the event, the program of which you can find here. Unfortunately, there had been 5 parallel sessions so if you wished to attend more than one of them at the same time, then you had a problem.

Day 1 (University day)

I chose to start my day with Maurice Naftalin's “Java Generics and Collections” speech. Maurice is the author with an excellent book with the same title. He presented a deep understanding on Generics issues, what to do and what to avoid, e.g. problems like casts and instanceof, parametric exceptions and problems with arrays. “Never ignore unchecked warnings” he said. Generics may have not had the great acceptance in the Java community yet, but I believe it is one of the positive additions of the language, and if you learn how to use them correctly, you can get great benefits from them.

After the break, I didn't watch the 2^nd part on Collections, as I also wanted to watch Sang Shin's “Introduction to Ajax”. Another excellent speaker, Sang maintains the Javapassion web site where he gives lessons in Java for free! If you check his site you 'll see a lot of information in almost every aspect of the language, and all this for free! Sang gave an overview of the main Ajax toolkits like Dojo, GWT, jMaki, JSF 2.0 with Ajax support etc. Amazing to watch this guy on stage.

After the lunch break, I attended “Seam in Action”. Seam is an extention to JSF, and as the speakers said, Seam is the new Struts. E.g. apart from Event, Session and Application, Seam also introduces the notions of Page, Conversation and Business Process. It seems to be a good extension and improvement upon JSF.

In the afternoon, I attended "BPM in action" using SoftwareAG's webMethods software, another tool for Business Process Modelling development. Unfortunately, the demo didn't work and so wasn't demonstrated by the good though speaker, Hilde Janssen.

Finally, I attended JetBrains' "Teamcity" tool. It seems to be an excellent tool for teamworking. Mike Aizatsky, an excellent speaker, demonstrated, using simple and to the point slides, the benefits of using the tool, which is now in version 3 and you can download it for free. E.g. one use of the tool is before the Version Control system, where it checks whether your code compiles before submitting it to version control. This way, you can be sure that only compiled versions are submitted to version control.

Day 2 (University day)

In day 2, the exhibition kiosks were set in place. The conference sponsors, like SUN, Adobe, Jboss, Intellij, Oracle, IBM and others, provided information about their products, and gave gifts to the participants. The participants could also participate in many video games and competitions. For example, the faster driver of a BMW emulator, brought by Cegeka, gained a PSP each day. JavaBlackBelt also had daily competitions; you had to answer 5 tricky multiple choice questions in a limited time. Those who had the best score and finished earlier participated in the finals for a PSP 3. And of course, Adobe, gave away O' Reilly books on Flex 2 and ActionScript. And there were many more gifts from other sponsors. This is the best part of Javapolis I think!

I began my second day with Bruce Eckel's presentation “Thinking in Flex”. Bruce moved to Adobe for those who didn't know. It was great to watch the author of one of the best Java books “Thinking in Java” live on the stage. Along with the help of Christophe Rooms, they presented Adobe Flex. It was a very good presentation and Flex 2 is a very impressive tool that now works with Java as the back end. I wish Java had the same impressive GUI components as Adobe Flex does. I avoided developing in Flash all these years because, however impressive the result of a Flash application is, the code is difficult to maintain. But with Flex and ActionScript you can create impressive Flash applications with a powerful scripting language that is easy to maintain. Even though a proprietary product, I 'll definitely give it a try. The new version of parleys.com is going to be built with this tool!

“JavaFX in Action” by Jim Weaver was my next attendance. I don't know if you have noticed, but there is a plethora or scripting languages nowadays and many more are developed. See e.g. Perl, PHP, Ruby, JavaScript, ActionScript, Wicket just to name a few. And many developers prefer to develop faster using a scripting languages. For many, scripting languages are the future of programming. Java's answer is JavaFX, a scripting language based in Java that allows you to develop quickly from swing applications for desktops, to mobile, or even web applications. SUN seems to have put a lot of effort in this new language, so I 'll give it a try and I suggest you do too.

In the afternoon I watched “Developing software like a band plays Jazz” presented by another legend, Erich Gamma, one of Gang of Four guys. Now employed by IBM, he presented Jazz, a collaboration product for enterprises. Erich addressed one of the main problems in companies today, lack of collaboration, which this tool addresses. Even though I didn't like the presentation, this tool seems to be of great help to software teams. And, it is an IBM product.

Day 3 (Conference day)

The day started with the speech of the father of Java, James Gosling, after a welcome by the event's responsible, Stephan Janssen, president of BeJUG, and an uncoference kick-off by Bruce Eckel. Three conference rooms where full just to watch the legend. The father of Java shared impressive statistics with the audience: 5 million Java enabled devices worldwide, 6 million Java developers, 12 million JRE downloads per week, 4 million Netbeans and 2.5 million Glassfish downloads. “If you are still using Emacs, then go shoot yourself”, said James, announcing Netbeans version 6.0. This new version has support for not only Java but also for Ruby, C++, Javascript and PHP. And as I say to my friends who use Visual Studio, just go and download Netbeans to see how Visual Studio 2012 is going to be like! James, also showed some impressive statistics regarding the speed of Java 6.0 which is now equal in speed or even outperforms C++! Far behind is C#, which is still very slow in all benchmarks. Finally, the father of Java asked the community to download and try JavaFX, where SUN puts a lot of effort in. We watched a couple of applications on Java, such as a very impressive demo of navigating two robots!

After this impressive beginning, the rest of the day continued with a presentation of “SoapUI”, a very good commercial product to test SOA applications, something that was actually missing from SOA apps.

“Google Web Toolkit” gave a nice overview of GWT also through the presentation of OpenSocial, an application developed by GWT.

The afternoon sessions were far more interesting. Instead of “Scrum in practice for non-believers”, Sander Hoogendoom gave a presentation on Anti-management practices or how to make your project fail! An excellent presentation that shows the reality in most software projects, and what to avoid to make your project succeed, or rather fail, in the speaker's words. He successfully presented common syndromes encountered today in project managers, architects, developers etc. The presentaiton is live on parleys.

The last presentation of the day was actually a Q&A with James Gosling, Joshua Bloch, Neal Gafter and Martin Odersky were the speakers answered questions posed by the audience. Not very successful in my opinion though.

Day 4 (Conference day)

The 2^nd conference day also started dynamically with a presentation of Adobe Flex by Bruce Eckel, followed by a speech of the Javapolis' creator, Stephan Janssen, who presented parleys.com version 2, built on Adobe Flex, and a keynote on JavaFX by Tim Cramer. We had the chance to see the possibilities of Netbeans 6 in developing mobile applications. Did you know that JME now comes with a games engine for mobile game applications?

After the break, I watched JPA 2.0 by Linda Demichiel, the chief architect of JPA at SUN Microsystems. With 20 years experience in IT, she gave an overview of JPA's new features and future work on it.

After the lunch break, the day was devoted to Joshua Bloch, an excellent speaker and author! The author of the most popular Java book “Effective Java”, changed his initial presentation and gave a presentation on Closures, a feature to be added to Java 7. Closures will allow to pass whole piece of code from one method to another. The speaker presented his skeptisism about this new feature and said that the language has already become too complicated to add yet another such complicated feature. And I wouldn't agree more with him. How many developers actually use most of Java 5's new features? Many still have problems to even understand Generics. Personally, I don't find Closures to be a useful addition to the language. We developers need the language to help us in solving our business or scientific problems in a simple and easy way, and I cannot see how Closures can help us in that. I don't see why to add a feature that will be used rarely or not at all by most of us. I would prefer to see improvements in the existing language syntax, like simplification or best practices of use of the features of the language, properties, even better performance etc.

Emmanuel Bernard gave next a presentation on “Hibernate search” or how to use Hibernate with Lucene to do efficient and effective full text searching.

Mark Janssen, author of “SOA using Java Web Services” book, gave a technical overview of how to develop web services with Java.

The day had the best ending ever with “The Java puzzlers” show by Joshua Bloch and Neal Gafter. Dressed with uniforms from Star Wars, they started their show by “fencing” with their “light pointers”! Each one of them posed alternatively 4 Java puzzlers to the other, and the audience had to answer which one of the 4 multiple answers was correct. These were new puzzlers to be added to “Java Puzzlers” version 2 book. If you haven't got this excellent book yet, what are you waiting for? Many participants bought it with 20% discount from the kiosk in the exhibition hall after this presentation!

This was the best day of the conference, ended with many more gifts, and competitions by the sponsor companies, as this was the last day of the exhibition. The day finshed by watching the movie “BeoWulf”.

Day 5 (Conference day)

The last day of the conference lasted only half a day and was not as good as the previous ones. “Wicket2”, presented by Martjin Dashorst, seems to be another very cool framework for building web applications using simply Wicket scripting language inside HTML for the presentation layer and Java for the business logic. No complicated things like JEE and EJB. Very promising framework which I 'll give it a try.

The rest presentations of the day were not that interesting. I started with OSGi, but I found the presentation rather boring and then left to watch “Innovating with Java” which I didn't find interesting either.

“Testing Driven Development” by the author Lasse Koskela of the book with the same name as the presentation, didn't say many new things to what I already know.

Thus, the conference finished.

A few final comments. The food was awful. An event, or something could also have been organised the last day of the conference to give us a better feeling of the last day and keep up our interest. Free drinks, like coke, sprite, water, even beer, were offered all five days. The exhibition was great!

You can watch all presentations from parleys.com when they become available. But of course, the value is to attend the conference, to live the excitement of these five days, to meet new people with same interests, to participate in the competitions and games, to get all these gifts, T-shirts, Cds, coffee cups, pens, bags etc. This is the spirit of Javapolis. See you there next year.

Greek and Java

2007-10-11T04:34:00.000-07:00

Under this subject I publish any issues that a Java programmer may encounter with Greek letters while writing Java programs. This information might be useful to programmers of other native languages too.

Issue 1: Apache Tomcat doesn't display Greek

Instead ???? are displayed.

Solution
You have to perform the following steps:

Edit conf/server.xml like so:

connector port="8080" maxhttpheader="8192" maxthreads="150" minsparethreads="25" maxsparethreads="75" enablelookups="false" redirectport="8443" acceptcount="100" connectiontimeout="20000" disableuploadtimeout="true" URIEncoding="ISO-8859-7" or URIEncoding="UTF-8" depending on your application.

If you are using a servlet, then you have to add the following lines of code to your doGet() method:

request.setCharacterEncoding("ISO-8859-7"); // or UTF-8 response.setCharacterEncoding("ISO-8859-7"); // or UTF-8

If you are using a JSP, then you must include the following header on the beginning of the jsp page:

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> // or ISO-8859-7
You may need to add this line too
// or ISO-8859-7
In case the encoding of the GET command is different than the one in URIEncoding (e.g. ISO-8859-7 and URIEncoding="UTF-8"), then use the command request.getQueryString() to get the original query string, before this is changed by Tomcat's URIEncoding, manually parse the string to a variable, e.g. myVar, and then use e.g. URLDecoder.decode(myvar, "ISO-8859-7").

Note: This info applies to JBoss too, as it is based on Tomcat.

References:

Issue 2: Greek support in Eclipse IDE

Right click an eclipse project and select Properties. In the info property, under Text file encoding box, select one of the following encodings:

ISO-8859-7
Cp1253
UTF-8

Issue 3: Greek support in Netbeans IDE

Right click on a project and select Properties. In the Encoding property, select one of the following encodings:

ISO-8859-7
Windows-1253
UTF-8

Issue 4: Greek support in MySQL

Use one of the following collations: utf8_unicode_ci or utf8_general_ci. Charset should be UTF-8.
If you are using phpmyadmin, you can do this while creating the database. If you have already created the database, you can change its collation by clicking on Operations tab.
If you can still not see Greek, edit my.conf and under [mysqld] tag add the string
character-set-server = utf8.

To use together with Tomcat:

url="jdbc:mysql://localhost/timesheet?useUnicode=true;characterEncoding=utf8" // or ISO-8859-7

Issue 5: Define encoding

Whenever you open/save a text file, specify the character encoding and don't rely on the OS default encoding:



Reader r = new InputStreamReader(new FileInputStream(file), "UTF-8"); // ISO-8859-7

Reader r = new InputStreamWriter(new FileInputStream(file), Charset.forName("ISO-8859-7"));

Writer w = new OutputStreamWriter(new FileOutputStream(file), "ISO-8859-7"); // UTF-8

Writer w = new OutputStreamWriter(new FileOutputStream(file), Charset.forName("UTF-8"));

String s = new String(byteArray, "UTF-8");

byte[] a = string.getBytes("UTF-8");    // Cp1253

Issue 6: Greek locale
private static final Locale GREEK_LOCALE = new Locale("el", "GR");

Issue 7: Greek and JEditorPane
Unfortunately, JEditorPane supports HTML 3.2 (to some arguable extend), while named Greek entities were added in HTML 4.0. This means, that

jEditorPane.setContentType("text/html");
jEditorPane.setText("αβγδ");
System.out.println(jEditorPane.getText());

will not return the Greek characters but something like

#965;#966;#967;#968

You can try

jEditorPane.setContentType("text/html;charset=utf-8");
jEditorPane.setText(new String("αβγδ".getBytes("utf-8"),"utf-8");

but it still doesn't work.

A solution is simply to use

jEditorPane.setContentType("text/plain");

In any case, it is better to handle the text from the variable it is stored than getting it from jEditorPane.getText().

References:

Java Anti-Patterns

Simple suggestions for 'team' programming

2007-09-26T00:35:00.000-07:00

Most programmers think that they are unique, that the way they program is the best, and they program only for themselves. This selfish attitude, however, does more bad than good. Working as a team has more advantages, less individual work, better cooperation to achieve deadlines, just to name a few, so why don't we (developers) learn how to cooperate?
Here I put four suggestions, which are so obvious to me, but I don't know why most programmers don't wish to follow:

Use and apply design patterns; they help better communication between the team as the provide for a common language; not to mention all the other advantages they provide, like extensible code, program to an interface etc.;
Don't hesitate to write javadoc and comments; they save another developer that looks at your methods and classes much time to know what it does than having to go through the code to realise what an uncommented method does;
Write test cases; they are mainly for documentation; they show another developer what is the input to a method and what to expect as an output than having to guess each time, especially when there is no javadoc;
Use this *bloody* CVS/SVN of yours correctly; add a comment each time you do a modification letting others know what you did and why. E.g. another guy just erased (or moved to another eclipse project) some classes in the team I work, and he never writes anything in CVS, letting me in nowhere of knowing why he did that and he 's too busy to ask.

If you have never heard of design patterns, then here are some references you may find useful:

Gamma E., Helm R., Johnson R., Vlissides J. (1995), Design Patterns – Elements of reusable components, Addison-Wesley.
Vlissides J. (1998), Pattern Hatching, Addison-Wesley.
Freeman, E. & Freeman, E. (2004), Head First Design Patterns, O’ Reilly.
Eckel, B. (2003), Thinking in Patterns with Java, http://mindview.net/Books/TIPatterns/
JavaCamp, http://javacamp.org/designPattern/index.html
Wikipedia, http://en.wikipedia.org/wiki/Design_Patterns

Write javadoc comments even to package or private methods explaining the algorithm that you use, any reference to a web site or book, and of course reference back to the use case or requirement that forced you to write this method. In eclipse it is also very easy to produce the html API by clicking on the project in package explorer and then to menu Project --> Generate Javadoc.

Creating junit test cases is also very easy with eclipse, just right click on the class you wish to test and choose New --> JUnit Test Case. Eclipse will ask you of the methods that you wish to test and will create the skeleton for you.

Next time you write a piece of code, think that you don't write it for yourself, but also for others who might review it or continue from where you left or need to modify it. Stop thinking selfishly; it doesn't help.

Heinz Kabutz also gave an interview on becoming a Better Programmer in SUN's website.

Secrets of Concurrency (Part 1) -- The Law of the Ritalin Child

2007-09-13T01:23:00.000-07:00

Do you read Heinz Kabutz's newsletter? I do, even though I don't always understand what a Java Champion such as Heinz means. :-) As I 'm not a Java champion and I don't think I 'll ever be, I sometimes spend quite a lot of time to follow Java champions' newsletters, speeches etc. :-)
This happened with his issue 146, "Secrets of Concurrency (Part 1) -- The Law of the Ritalin Child". To understand this newsletter, on a difficult topic such as threads, I had to create some drawings on a piece of paper. So, for all the rest of you who didn't understand exactly what that issue says, or who didn't bother to look more seriously into it, here I put a drawing and my understanding of it.

So, back to our subject. The first question Heinz poses in his newsletter is what does InterruptedException mean?
Let's first examine when an InterruptedException is thrown. A thread can be in any one of the states that are shown in the following state transition diagram, i.e. NEW, RUNNABLE, BLOCKED, WAITING, TIMED_WAITING and TERMINATED. See java.lang.Thread.State if you don't believe me.

Now, assume that our thread, lets call it thisThread, is in the RUNNABLE state. Heinz says that
"[i]f the thread is not in a waiting state, then only the interrupted status is set, nothing else."
I.e., if thisThread's state is RUNNABLE, and it calls its interrupt() method, the only thing that happens is that thisThread.interrupted=true. In other words:

// thisThread is in RUNNABLE state
// when
thisThread.interrupt();

then the following occurs:

thisThread.interrupted=true;

"If the thread is currently in either the WAITING or TIMED_WAITING states, it immediately causes an InterruptedException and returns from the method that caused the waiting state."
I.e., if thisThread's state is either WAITING or TIMED_WAITING, and its interrupt() method is called, it throws an InterruptedException and returns from the method that caused the waiting state. Its interrupted status should already be true. However, as we shall see later, when an InterruptedException is thrown, the interrupted status of the thread is flipped back to false. In other words:

// thisThread is in WAITING or TIMED_WAITING state

// when
thisThread.interrupt();

then an InterruptedException is thrown and
thisThread.interrupted=false;

"However, if later on the thread calls a method that would change the state into WAITING or TIMED_WAITING, the InterruptedException is immediately caused and the method returns."
I.e. if thisThread.interrupted=true, because its interrupt() method was called previously, and thisThread called a method that causes a state transition to one of either WAITING or TIMED_WAITING states, then, because thisThread.interrupted is already true, an InterruptedException is immediately thrown and its state remains to RUNNABLE. In other words:

// thisThread is in RUNNABLE state

thisThread.interrupted=true;
// when

thisThread.wait();

then

thisThread.State=RUNNABLE
an InterruptedException is thrown and
thisThread.interrupted=false;

But how can thisThread change its state to WAITING or TIMED_WAITING? By calling one of the following methods: wait(), Thread.sleep(), BlockingQueue.get(), Semaphore.acquire() and Thread.join().

E.g.

try {
Thread.sleep(1000); // 1 second
} catch(InterruptedException ex) {
  // ignore - won't happen
}

"Note that attempting to lock on a monitor with synchronized puts the thread in BLOCKED state, not in WAITING nor TIMED_WAITING. Interrupting a thread that is blocked will do nothing except set the interrupted status to true. You cannot stop a thread from being blocked by interrupting it. Calling the stop() method similarly has no effect when a thread is blocked. "
OK? Did you get that? If thisThread.State=BLOCKED, calling its interrupt() method, simply causes thisThread.interrupted=true while calling its stop() method has no effect.

The interrupted status is nowadays commonly used to indicate when a thread should be shut down because it is thrown at well defined places that wouldn't cause any problems, not like Thread.stop() method. The problem with the Thread.stop() method was that it would cause an asynchronous exception at any point of the thread's execution code.

"Note that the interrupted status is set to false when an InterruptedException is caused or when the Thread.interrupted() method is explicitly called. Thus, when we catch an InterruptedException, we need to remember that the thread is now not interrupted anymore! In order to have orderly shutdown of the thread, we should keep the thread set to "interrupted"."

So, what should we do when we call code that may cause an InterruptedException? Heinz has two answers on this:

Rethrow the InterruptedException from your method.
Catch it, set interrupted status, return

E.g.

while (!Thread.currentThread().isInterrupted()) {
   // do something
   try {
TimeUnit.SECONDS.sleep(1000);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
      break;
}
}

Remember! Don't just ignore interruptions, deal with the cause!

So, to recap:

if a thread is in RUNNABLE state and its interrupt() method is called, its interrupted status changes to true;
if a thread is in WAITING or TIMED_WAITING state and its interrupt() method is called, it throws an InterruptedException and its interrupted status changes back to false;
if a thread is in RUNNABLE state and one of its methods that changes its state to WAITING or TIMED_WAITING is called, and, previously its interrupted status has been set to true by a call to its interrupt() method, then an InterruptedException is thrown, its state changes to RUNNABLE and its interrupted status changes back to false;
finally, if a thread is in BLOCKED state and its interrupt() method is called, its interrupted status changes to true; while nothing seems to happen when its stop() method is called. (It seems that if there is a lot of contention for locks, the stop signals get lost).

Actually, for the last case, this can be checked by the following piece of code (contributed by Heinz):


public class CheckBlocking {

   public static void main(String[] args) throws InterruptedException {
 Thread t1 = new Thread() {
 public void run() {
   while (true) {
     System.out.println("t1");
     synchronized (CheckBlocking.class) {
      try {
        CheckBlocking.class.wait(10000);
      } catch (InterruptedException e) {
        interrupt();
        return;
      }
   }
  }
}
};
Thread t2 = new Thread() {
public void run() {
 while (true) {
  System.out.println("t2 blocked");
    synchronized (CheckBlocking.class) {
      System.out.println("t2");
      try {
        CheckBlocking.class.wait(950);
      } catch (InterruptedException e) {
        interrupt();
        return;
      }
    }
  }
}
};

t1.start();
Thread.sleep(2000);
t2.start();
Thread.sleep(2000);
t2.stop();
}
}

If you run this code, you will notice that no exception is thrown. It gets lost somewhere.

Thanks Heinz.

For those of you who want to learn about Java threads, I would recommend "Java concurrency in practice" by Brian Goetz, Tim Peierls, Joshua Bloch, Joseph Bowbeer, David Holmes, Doug Lea, the only book in my opinion that explains in plain english and allows you to understand what is going on in multithreading java and the strange behaviour of your multithreading programs, if you have encountered such.

java.util.Formatter

2007-09-12T02:32:00.000-07:00

Since JDK 1.5, java has java.util.Formatter class, an interpreter for printf-style format strings. However, the API for java.util.Formatter is rather obscure to understand. This blog is to help you see each format command and its result and be able to use the most appropriate format string for your case right away, without the need to go through the long Java API for this class.

The following info applies to:

Formatter.format()
String.format()
java.io.PrintStream.format()
java.io.PrintWriter.format()
printf()

but String.format() is only shown here for convenience. The same arguments can be used for the other 2 methods.

Here is a test case to display the use of format strings for date/time. I use this date as an example: 07-01-2007 22:05:01 (7th of January 2007, my name day!)

import java.text.SimpleDateFormat;
import java.util.Calendar;

import junit.framework.TestCase;


/**
* Class to test java.util.Formatter
* @author jkost
* @see java.util.Formatter
* @since JDK 1.5
*/
public class FormatterTester extends TestCase {
    private final SimpleDateFormat sf = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
    private Calendar cal = Calendar.getInstance();

    protected void setUp() throws Exception {
 super.setUp();
cal.setTime(sf.parse("07-01-2007 22:05:01"));
}
/**
* Conversion characters for formatting dates.
*
*/
    public void testDateFormatter() {
// full day of week
assertEquals("Sunday", String.format("%tA", cal));
// abbreviated day of week
assertEquals("Sun", String.format("%ta", cal));
// full month name
assertEquals("January", String.format("%tB", cal));
// abbreviated month name
assertEquals("Jan", String.format("%tb", cal));
assertEquals("Jan", String.format("%th", cal));
// the century, 00 to 99, i.e. year divided by 100
assertEquals("20", String.format("%tC", cal));
// day of month, 2-digit format
assertEquals("07", String.format("%td", cal));
// day of month, 1-digit format, i.e. without leading zeros
assertEquals("7", String.format("%te", cal));
// Date formatted as "m/d/y" (short numeric form)
assertEquals("01/07/07", String.format("%tD", cal));
// ISO 8601  complete date formatted as "Y-m-d".
assertEquals("2007-01-07", String.format("%tF", cal));
// 3-digit day of year
assertEquals("007", String.format("%tj", cal));
// 2-digit, month of year
assertEquals("01", String.format("%tm", cal));
// no week of year; SUN needs to implement this
// assertEquals("01", String.format("%tw", cal));
// 4-digit year
assertEquals("2007", String.format("%tY", cal));
// last 2 digits of year
assertEquals("07", String.format("%ty", cal));
}

/**
* Conversion characters for formatting times.
*
*/
    public void testTimeFormatter() {
// 24-hour of day, 2-digit format, 00-23
assertEquals("22", String.format("%tH", cal));
// 12-hour of day, 2-digit format, 00-12
assertEquals("10", String.format("%tI", cal));
// 24-hour of day, 1-digit format, 0-23
assertEquals("22", String.format("%tk", cal));
// 12-hour of day, 1-digit format, 0-12
assertEquals("10", String.format("%tl", cal));
// minutes, 2-digit format, 00-59
assertEquals("05", String.format("%tM", cal));
// seconds, 2-digit format, 00-59
assertEquals("01", String.format("%tS", cal));
// milliseconds, 3-digit format, 000-999
assertEquals("000", String.format("%tL", cal));
// nanoseconds, 9-digit format, 000000000 - 999999999
assertEquals("000000000", String.format("%tN", cal));
// am or pm
assertEquals("pm", String.format("%tp", cal));
// AM or PM
assertEquals("PM", String.format("%Tp", cal));
// RFC 822  style numeric time zone offset from GMT, e.g. -0800.
assertEquals("+0100", String.format("%tz", cal));
// the abbreviation for the time zone
assertEquals("CET", String.format("%tZ", cal));
// Seconds since the beginning of the epoch starting at 1 January 1970 00:00:00 UTC,
// i.e. Long.MIN_VALUE/1000 to Long.MAX_VALUE/1000.
assertEquals("1168203901", String.format("%ts", cal));
// Milliseconds since the beginning of the epoch starting at 1 January 1970 00:00:00 UTC,
// i.e. Long.MIN_VALUE to Long.MAX_VALUE.
assertEquals("1168203901000", String.format("%tQ", cal));
// Time formatted for the 24-hour clock as "%tH:%tM"
assertEquals("22:05", String.format("%tR", cal));
// Time formatted for the 24-hour clock as "HH:MM:SS".
assertEquals("22:05:01", String.format("%tT", cal));
// Time formatted for the 12-hour clock as "hh:mm:ss AM/PM"
assertEquals("10:05:01 PM", String.format("%tr", cal));
}

/**
* Conversion characters for formatting date/time compositions.
*
*/
    public void testDateTimeFormatter() {
// Date and time formatted as e.g. "Sun Jul 20 16:17:00 EDT 1969".
assertEquals("Sun Jan 07 22:05:01 CET 2007", String.format("%tc", cal));
}

/**
* Formats the value as either "true" or "false" (or "TRUE" or "FALSE", for %B).
* For boolean values, this works as expected.
* For all other values, any non-null value is "true", while null values are "false".
* %type
* type = b | B | s | S
*
*/
public void testBooleanFormatter() {
final boolean flag = true;
// boolean
assertEquals("true", String.format("%b", flag));
// boolean
assertEquals("TRUE", String.format("%B", flag));

// as string
assertEquals("true", String.format("%s", flag));
assertEquals("TRUE", String.format("%S", flag));

assertEquals("false", String.format("%b", null));
assertEquals("true", String.format("%b", 1));
assertEquals("true", String.format("%b", 'a'));
}

/**
* Formats the value supplied as a single character.
* Supplied value must be a Byte, Short, Character, or Integer.
* %[argument][width]type
* argument = <
* width = any positive integer value
* type = c | C | s | S
*
*/
public void testCharacterFormatter() {
final char c = 'a';
// character
assertEquals("a", String.format("%c", c));
// character
assertEquals("A", String.format("%C", c));
// as string
assertEquals("a", String.format("%s", c));
assertEquals("A", String.format("%S", c));
}

/**
* %[argument][flags][width]type
* argument = < 
* flags = - | + | # |  | ( | 0 
* width = any positive integer value
* type = d | o | x | X | H | s
* Arguments must be Byte, Short, Integer, Long, or BigInteger.
*/
public void testIntegerFormatter() {
final int intNumber = 7;

// base-10 integer
assertEquals("7", String.format("%d", intNumber));

// base-8 (octal) integer
assertEquals("16", String.format("%o", 2*intNumber)); // 2*7 = 14

// flag '#' indicates that formatted output should appear in alternate form.
// For %o, this means a leading 0.
assertEquals("07", String.format("%#o", intNumber));

// base-16 (hexadecimal) integer
assertEquals("e", String.format("%x", 2*intNumber)); // 2*7 = 14
assertEquals("E", String.format("%X", 2*intNumber)); // 2*7 = 14

// flag '#' indicates that formatted output should appear in alternate form.
// For %x and %X, output will include a leading 0x (0X).
assertEquals("0x7", String.format("%#x", intNumber));
assertEquals("0X7", String.format("%#X", intNumber));

// hexadecimal representation of the value's hashcode
assertEquals("e", String.format("%h", 2*intNumber));  // 2*7 = 14
assertEquals("E", String.format("%H", 2*intNumber));  // 2*7 = 14

// as string
assertEquals("7", String.format("%s", intNumber));

// width 3
assertEquals("  7", String.format("%3d", intNumber));

// flag '-' means left justification
assertEquals("7  ", String.format("%-3d", intNumber));

// flag '+' indicates that numeric output should always include a sign (+ or -).
assertEquals("+7", String.format("%+d", intNumber));

// flag '(' indicates that negative numbers should appear in parentheses.
assertEquals("(7)", String.format("%(d", -intNumber));

// flag '0' indicates that numeric values should be padded on the left.
assertEquals("007", String.format("%03d", intNumber));

// flag ' ' (space) indicates that non-negative values should be prefixed with a space
// (for alignment with negative numbers).
assertEquals(" 7", String.format("% d", intNumber));

// flag '#' indicates that formatted output should appear in alternate form.
// For %s and %S, the flag is passed on to the object's formatTo( ) method.
// The # flag only works in conjunction with %s and %S if the argument
// implements java.util.Formattable.
assertEquals("7", String.format("%#s", intNumber));

// argument < indicates that the previous argument should be used (again),
// rather than continuing on
assertEquals("+7   7", String.format("%+d %<3d", , intNumber));
}

/**
* %[argument][flags][width][.precision]type
* argument = <
  * flags = - | + | # |  | ( | 0 | ,
  * width = any positive integer value
  * precision = any positive integer value
  * type = f | a | g | G | e | E | h | H | s
  * Arguments must be Float, Double, or BigDecimal.
  */
public void testDoubleFormatter() {
final double doubleNumber = 7.0d;

// double/float number, 6 decimal digits by default
assertEquals("7.000000", String.format("%f", doubleNumber));

// double/float number, 5 max decimal digits
// precision is the total number of significant digits to be displayed
assertEquals("7.00000", String.format("%g", doubleNumber));
assertEquals("7.00000", String.format("%G", doubleNumber));

// exponential notation, default number of decimal digits 6
assertEquals("7.000000e+00", String.format("%e", doubleNumber));
assertEquals("7.000000E+00", String.format("%E", doubleNumber));

// exponential notation, using base-16 for the decimal part,
// and base-10 for the exponent part
assertEquals("0x1.cp2", String.format("%a", doubleNumber));

// hexadecimal representation of the value's hashcode
// precision determines the maximum characters output
assertEquals("401c0000", String.format("%h", doubleNumber));
assertEquals("401C0000", String.format("%H", doubleNumber));

// as string
// precision determines the maximum characters output
assertEquals("7.0", String.format("%s", doubleNumber));

// 2 decimal digits (precision = 2)
assertEquals("7.00", String.format("%.2f", doubleNumber));

// width 6, precision = 2 (2 decimal digits)
assertEquals("  7.00", String.format("%6.2f", doubleNumber));

// flag '-' means left justification
assertEquals("7.00  ", String.format("%-6.2f", doubleNumber));

// flag '+' indicates that numeric output should always include a sign (+ or -).
assertEquals(" +7.00", String.format("%+6.2f", doubleNumber));

// flag '(' indicates that negative numbers should appear in parentheses.
assertEquals("(7.00)", String.format("%(.2f", -doubleNumber));

// flag '0' indicates that numeric values should be padded on the left.
assertEquals("007.00", String.format("%06.2f", doubleNumber));

// flag ',' indicates that the locale-specific grouping character
// should be used for numeric values.
assertEquals("7,00", String.format(new Locale("el"), "%,.2f", doubleNumber));

// flag ' ' (space) indicates that non-negative values should be prefixed with a space
// (for alignment with negative numbers).
assertEquals(" 7.00", String.format("% .2f", doubleNumber));


// argument < indicates that the previous argument should be used (again),
// rather than continuing on
assertEquals("7.00 7.0", String.format("%.2f %<3.1f", doubleNumber));
}    

public void testIntegerNumberFormatter() { 
final double intNumber = 7;

// another way to format integers
NumberFormat nf = NumberFormat.getInstance();
nf.setMinimumIntegerDigits(3);
nf.setParseIntegerOnly(true);
assertEquals("007", nf.format(intNumber));
}
}