JHUG meetup February 28th 2018

The first JHUG meetup for 2018 was held at the premises of Advantage FSE. Ms Peggy Theodorou-Zoumi on behalf of Advantage FSE, welcomed the members of JHUG at their premises for yet another more time as they are fond supporters of our group and they too believe that people are the most important value in our industry.

After this warm welcome the organizers Thomas and Spyros took the word to motivate members to give talks for the forthcoming events. Since both of them are experienced engineers there was a clear separation of concerns in their calls and one asked for subjects while the other for speakers.


I want you to speak about subjects you don’t know anything about but you find interesting and you are curious. Do some research, experiment a bit and come to give a talk. I am sure it will be very good.


Our community is growing and there are many new faces in each meetup. The best way to get to know each other is a lightning talk. Come up and tell us who you are, what you are working on, what you have to tell and what you want to hear. A lightning talk for 10 minutes on any topic is very easy to do and will help to evolve and grow the community even more.

There is a form to declare your interest in giving a talk and we urge you to submit a proposal. Remember that the most important thing for a talk in communities like ours it to create traction and empathy. The value of the talk is important but secondary.

And now the major part, the talks.

The first speaker was Antonis Lilis of Advantage FSE. He is a regular member of JHUG and has given us very interesting talks on mobile computing. For this meetup he chose to talk about

A short introduction to the Kotlin language for Java Developers

Kotlin is a language for the JVM developed by JetBrains. It was released as open source in 2012 and there was a major interest in it when Google announced it as a language for Android development in 2017.

The talk was targeted to programmers familiar with Java. Antonis presented in a concise, sweet and up to the point way the features of Kotlin that make it both attractive and productive. It is not an academic language or an experiment, it is designed for modern applications.

It runs on the JVM but it is not an extension or an upgrade to Java. Familiarity with Java helps a lot to reduce the learning curve but it is not a prerequisite.

Kotlin is a statically typed language that supports both object-oriented and functional paradigms. It has first class functions, type inference, some nice syntactic shortcuts like null check operators, safe casting, companion objects and many more structures that look natural in Kotlin but compared with Java they greatly reduce boilerplate code. Kotlin also supports composition instead of inheritance as the primary mechanism for extending classes and has data classes which in essence are value classes generated by the compiler. It has also a proposal for structure concurrency in coroutines which you can think of as very lightweight threads. The slides are very descriptive and you can start programming in Kotlin just be reading them.

It is supported by all major IDEs. The toolchain for it is quite stable and keeps improving as the language gains interest.

At the end Antonis answered questions about the stability and the future of the language.

In my opinion Kotlin is another language for the JVM like scala, groovy, clojure and it has to answer the same question: It certainly makes programs easier to write but are there any safeguards to preserve the readability? We have seen examples of scala and groovy where programs become completely unreadable because of feature abuse and not forget that one of the advantages of Java is that it has the same readability/writeability ratio. The advantage for Kotlin is that is has a very suitable environment for it as it is a first citizen language for Android and the characteristics of mobile apps favor such high level languages.

Kotlin is definitely a project to track and this talk by Antonis did a great job to promote it.

Pizza, Beers and Networking

This is one of the best parts of every meetup. A break during the two talks for pizza and beers kindly offered by our host Advantage FSE. There was a full round of networking to meet other JHUG members and talk about interesting debugging stories, production failures, upcoming technologies, vim vs emacs etc For this meetup the topic was Kotlin and how Java/Scala/Ruby/Awk does a better job 🙂

Istio – Service mesh

The second talk was delivered by Georgios Andrianakis of RedHat. He chose to present Istio a new and trending technology which most attendees were not acquainted with. The talk was intended for newcomers and it was also a tutorial for service meshes in general.

Georgios started describing microservices architectures and how their essence, that no matter how you design them they are a distributed system and underneath them there is an unreliable network, is the cause of most problems. He then presented and analyzed the major architectural challenges regarding distributed systems like resilience, fault tolerance, load balancing, canary deployments and discussed potential solutions. It seems there are two approaches:

The old one was to use state of the art code libraries like hystrix, zuul, zipkin and embed reliability in the application. That proved inadequate for medium to large installations as code maintenance costs became intolerable even for large organizations.

The modern approach is to develop a _platform_ in which you deploy your microservices and the platform takes care of all the architectural challenges and production issues. An important step towards that direction was Kubernetes which to oversimplify manages your cluster and provides a platform that handles discovery, invocation, elasticity and monitoring. Thaw was important but not enough. The next step is the *service mesh* which in Georgios words is

a decentralized, application networking infrastructure between your services that provides resilience, security, observability and routing control

Then he proceeded to present Istio, its architecture and a typical setup. To demonstrate the benefits he presented a setup with 2 services talking to each other and analyzed the whole request/response cycle between them and how Kubernetes and Istio combined _tame_ the network.

The slides are excellent and repay study. You can find them here.

That was an excellent talk and this what JHUG is about. A good talk on a promising technology that inspires you to explore it and who knows maybe prepare a new talk for it for a next meetup (suggestion: do it!).


After the talks there was a draw for one copy of Kotlin in Action and we updated our meetup for the beginning of April. Stay tuned for the details at meetup, twitter and slack.

JHUG event – February 2018

Το meetup του Φεβρουαρίου θα φιλοξενήσει η Advantage FSE.

Οι ομιλίες:

A short introduction to the Kotlin language for Java Developers – Antonis Lilis [1]

Do you like Java but wish you didn’t have to write so much boilerplate code? Kotlin aims to address many of the pitfalls that are common with Java development, while making your code more concise, safe, and expressive. It is also 100% interoperable with Java and can be mixed in the same project.

Introduction to Istio Service Mesh – Georgios Andrianakis [2]

The purpose of the presentation is an introduction to the Istio project. We will explore what it can offer to those who want to develop Microservices.

Ενδεικτικό πρόγραμμα

• 18.30 – Προσέλευση/ έλεγχος εισόδου

• 19.00 – 19.15 Παρουσίαση χορηγου

• 19.15 – 20.15 – Ομιλία για Kotlin

• 20.15 – 20.30 Πίτσα/μπυρα/πηγαδάκια/networking

• 20.30 – 21.30 Ομιλία για Istio

Κρατάτε μαζί σας την ταυτότητα σας για λόγους ασφαλείας στην εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)

[1] http://www.linkedin.com/in/alilis
[2] https://www.linkedin.com/in/georgios-andrianakis-71305815

JHUG event – November 2017

Το επόμενο meetup θα φιλοξενήσει η Eurobank στις 28 Νοεμβρίου. RSVP εδώ.

Για τη γενική τοποθεσία μπορείτε να δείτε το χάρτη. Το meetup θα γίνει στο Κτίριο Η / συνεδριακό κέντρο. Μόλις έχουμε αναλυτικές οδηγίες για το πώς μπορείτε να έρθετε, θα τις αναρτήσουμε.

Οι ομιλίες:

Using JCache to speed up your apps – Vassilis Bekiaris (Linkedin)

JCache (JSR-107) is the standardized way to temporarily cache data in your Java apps. In this talk, we will explore basic caching concepts, introduce the JCache API and go through sample caching use cases covering basic usage and integration scenarios.

Going to production with Docker, Kubernetes and Java microservices – Anestis Georgiadis (Linkedin)

An overview of the journey to production for a system being built from the bottom up as cloud-native. We will be presenting architectural choices for the Java stack, development tooling based on Docker, the value of Kubernetes and things to consider overall before embarking on a similar journey.

Ενδεικτικό πρόγραμμα

• 18.30 – Προσέλευση/ έλεγχος εισόδου

• 19.00 – 19.15 Παρουσίαση χορηγου

• 19.15 – 20.15 – Ομιλία για JCache

• 20.15 – 20.30 Πίτσα/μπυρα/πηγαδάκια/networking

• 20.30 – 21.30 Ομιλία για Docker, Kubernetes και Java Microservices

Κρατάτε μαζί σας την ταυτότητα σας για λόγους ασφαλείας στην εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)

JHUG event – May 2017

Η εταιρία Agile Actors θα μας φιλοξενήσει στις 12 Μαΐου για το επόμενο meetup (RSVP εδώ)

Οι ομιλίες:

• A Gentle Introduction to Cassandra Database – part 2 (Πέτρος Κακλαμάνης)

Μία απο τις πιο γνωστές NoSQL Βάσεις Δεδομένων είναι η Cassandra DB, δημοφιλής για τα εξής χαρακτηριστικά της: availabilty, scalability, και predictable performance. Σε αυτήν τη δεύτερη παρουσίαση θα εστιάσουμε στους μηχανισμούς της για Lightweight Transactions, καθώς και σε τεχνικές μοντελοποιήσης δεδομένων για αυτήν (Data Modeling, and Schema Design) με παραδείγματα σε CQL και Java. Μπορείτε να παρακολουθήσετε το πρώτο μέρος της παρουσίασης εδώ.

• Reactive Extensions for Java (Σπύρος Αναστασόπουλος)

Οι reactive επεκτάσεις για java είναι ένα ακόμα ένα σύγχρονο topic/buzzword. Σύμφωνα με το site, είναι ένα “API for asynchronous programming with observable streams”, ένας ορισμός πολύ γενικός και διφορούμενος καθώς ισχύει για όλα τα frameworks που περιέχουν έστω και εν μέρη την έννοια του data pipeline. Σε αυτή την εισαγωγή θα παρουσιαστεί η υλοποίηση του παραπάνω spec σε java (βλέπε εδώ) μαζί με τυπικές αρχιτεκτονικές και παραδείγματα χρήσης. Η ομιλία είναι εισαγωγική και δεν προυποθέτει εξοικείωση με το domain.

Συμβουλευτείτε το χάρτη.


• 18.30 – Προσέλευση/ έλεγχος εισόδου

• 18.45 – 19.45 Ομιλία για Apache Cassandra

• 19.45 – 20.00 – Ομιλία χορηγού

• 20:00 – 20:30 Πίτσα/πηγαδάκια/networking

• 20:30 – 21.30 Ομιλία για Reactive Extensions

Για λόγους ασφαλείας, παρακαλούμε κρατάτε μία ταυτότητα για την εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)

Βίντεο: Ομιλίες για Refactoring και Microbenchmarks – Μαρτιος 2017

Java Hellenic User Group | Η ελληνική κοινότητα προγραμματιστών Java

Παρουσιαση 1 – Refactoring in Practice

Παρουσιαση 2 – Microbenchmarking with JMH

Περιμένουμε τις δικές σας ιδέες για παρουσιάσεις. Οποιοδήποτε θεμα
εχει σχεση με Java και σας ενδιαφέρει μπορεί να γίνει παρουσίαση. Δεν
είναι ανάγκη να ειναι κατι προχωρημένο, αρκεί να σας αρέσει.

Κάντε την προταση σας ειτε στο https://www.meetup.com/Java-Hellenic-User-Group/ είτε στην λίστα https://groups.google.com/forum/?fromgroups#!forum/jhug

Ραντεβου στην επόμενη συνάντηση!

JHUG event – March 2017 #jhug #java

Η εταιρία Trasys Greece (πλέον μέρος του NRB Group) θα μας φιλοξενήσει για το meetup του Μαρτίου.

Παρακαλούμε RVSP εδώ.

Οι ομιλίες:

• Refactoring in Practice (Panagiotis Kapralos)

This presentation is an overview of the Refactoring practice. Starting with an example, it demonstrates how you can improve existing code by applying a series of small behavior preserving transformations.

Following a brief discussion on the motivation and economic justification of Refactoring, it will provide some real world advice: how to improve your code with confidence, how to keep your work focused, how to incorporate refactoring in your development workflow, how to avoid common pitfalls, and more.

The level of this presentation is introductory, so anyone with basic understanding of software engineering should be able to follow.

• Microbenchmarks, Introducing JMH (Giorgos Kalfopoulos)

Microbenchmarks, what are they? Why are they hard? An explanation of the difficulties caused by JVM Hotspot optimizations and how to overcome them using JMH, a toolkit created by the same people that create the JVM. Wrapping up with a real-life example implemented with JMH, explaining some of JMH key concepts along the way.

The level of this presentation is introductory, but the topic is not. Most people will be able to follow but if they have not bothered with benchmarks/performance testing they have some difficulty grasping everything.

Συμβουλευτείτε το χάρτη.


• 18.00 – Προσέλευση/ έλεγχος εισόδου

• 18.15 – 19.15 Ομιλία για refactoring

• 19.15 – 19.30 – Ομιλία χορηγού

• 19:30 – 19:45 Πίτσα/πηγαδάκια/networking

• 20.00 – 21.00 Ομιλία για Microbenchmarks

Για λόγους ασφαλείας, παρακαλούμε κρατάτε μία ταυτότητα για την εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)

Netbeans day 21 Απριλίου 2017 (είσοδος ελευθερη)

Tο NetBeans περνάει μια μεταβατική περίοδο της ζωής του καθώς περνάει στο Ίδρυμα Apache. Για να μάθετε περισσότερα γι’ αυτή την κίνηση καθώς και τα τελευταία νέα που αφορούν το NetBeans IDE και την πλατφόρμα NetBeans Rich Client, η Κοινότητα του NetBeans σε συνεργασία με τη UniSystems, σας προσκαλούν στις  21 Απριλίου σε μια ελεύθερη εκδήλωση.

Οι ημερίδες NetBeans λαμβάνουν χώρα σε διάφορες χώρες ανά τον κόσμο, από το JavaOne 2014, όπου συνελήφθη η ιδέα. Αδράξτε την ευκαιρία να ενημερωθείτε για τις τελευταίες εξελίξεις σχετικά με το NetBeans IDE και την πλατφόρμα NetBeans από ειδικούς του χώρου.

Πρόχειρη Ημερήσια διάταξη:

9:30-10:00: Εγγραφές, καφές

10:00-10:30: Welcome and NetBeans roadmap (Geertjan Wielenga: NetBeans Product Manager, Oracle)

10:30-10:45: Διάλειμμα

10:45-12:00: Oracle JET – workshop (Geertjan Wielenga: NetBeans Product Manager, Oracle)

12:00-13:00: Μεσημεριανό διάλειμμα

13:00-14:00: NetBeans support for EcmaScript 6 (ΚώσταςΣαϊδής: Niovity)

14:00-15:00: Writing better code with NetBeans (Sophia Matarazzo & Bethan Palmer: IDR Solutions, UK)

15:00-15:15: Διάλειμμα

15:15-16:15: Spring Boot made easy with NetBeans; real world examples (Αλέξης Διακογιάννης, UniSystems)

16:15-17:00: Developing Scala applications using NetBeans (Πάτροκλος Παπαπέτρου: Chief Software Architect @ Crossover)

17:00-17:30: Converting a Swing application to Dukescript (Γιάννης Κωστάρας)

Περισσότερες λεπτομέρειες εδω


JHUG December 2016 – Meetup- Links and Vids

Java Hellenic User Group | Η ελληνική κοινότητα προγραμματιστών Java

Παρουσιαση 1 – Building Maintainable Software part 2

Παρουσιαση 2 – Apache Cassandra

Μην ξεχασετε οτι μπορειτε και εσεις να κάνετε μια παρουσιαση.Οτι θεμα σας ενδιαφέρει και ειναι σχετικο με προγραμματισμό Java είναι ευπρόσδεκτο

Κάντε την προταση σας ειτε στο https://www.meetup.com/Java-Hellenic-User-Group/ είτε στην λίστα https://groups.google.com/forum/?fromgroups#!forum/jhug

JHUG December Meetup – Maintainability / Apache Cassandra – 2 Dec

Λιγο πριν τελειωσει το έτος, κανονίσαμε άλλη μια συνάντηση του συλλόγου JHUG

Αυτην την φορά θα μας φιλοξενήσει η εταιρία Advantage στα νότια της Αθήνας

Οι ομιλητές:

Μάριος Κόγιας (Linkedin): “Maintainability: The starting guidelines for easily readable Java Source Code”. Θα γίνει το δευτερο μέρος της παρουσίασης. Δείτε το πρώτο μερος στο βιντεο.

Πέτρος Κακλαμάνης : “Introduction to Apache Cassandra NoSql”

Δείτε τον χάρτη.

Αυτην την φορά η Advantage είχε την ευγενική πρωτοβουλια να λειτουργήσει ως διπλός χορηγός προσφέροντας και τον χώρo αλλα και το κέρασμα.


• 18.30 – Προσέλευση/ έλεγχος εισόδου

• 19.00 – 19.15 Παρουσίαση χορηγου

• 19.15 – 20.15 – Ομιλία για readable Java

• 20.15 – 20.30 Πίτσα/μπυρα/πηγαδάκια/networking

• 20.30 – 21.30 Ομιλία για Apache Cassandra

Κρατάτε μαζί σας την ταυτότητα σας για λόγους ασφαλείας στην εισοδο.

Σας περιμένουμε!

(Είσοδος ελευθερη)

Για έγγραφές μπείτε στο meetup