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London Java Community

The home for those who work with Java and the JVM

What is LJC about?

The LJC is a broad community of technologists and other associates with Java and JVM-related technologies. Although it is based in London, UK – it has some international membership due to its global programmes (such as Adopt a JSR and Adopt OpenJDK). The LJC hosts regular events including casual catch-ups in a cafe, hack days, evening talks, unconferences, workshops, mentoring, demos, a career mentoring by London’s
Java specialists and much more.

The LJC acts as a voice for Java engineers in London UK as well as globally. This includes but is not limited to creating Adoptium, the world’s leading OpenJDK distribution, representing Java developers worldwide on the Java standards body, and contributing towards charitable works.

Upcoming Event

LJC Meet-up

The LJC is delighted to continue our new series of events, aimed at giving all Community members an opportunity to present at an LJC meet-up. If you have an interesting topic to share, these events are for you. You don’t have to be an experienced speaker - we want to hear your story and offer you a friendly, informal platform to practise and improve your presentations. For attendees we want this to be a meeting place, where you can talk and network with other technologists in London. If you’d like to speak at a future event, please submit your talk and bio details here: https://sessionize.com/ljc/ Huge thanks to our friends at Couchbase for hosting this event and supporting our Community. Agenda: 6pm Arrivals 6.20 Welcome from Couchbase 6.30 Presentation 1 7.15 Break for refreshments, kindly provided by Couchbase 7.45 Presentation 2 8.30 Networking 9pm Event closes Speaker: Salman Shah, Senior Software Engineer, Smartsheet Talk: Unlocking Java's Multiprocessing Potential: A Journey from Basics to Virtual Threads Join us on a journey as we explore the evolution of multiprocessing in Java, from its humble beginnings to the recent introduction of virtual threads in JDK 21. We'll delve into the basics of multiprocessing, discussing various techniques and frameworks available, and examine the significance of virtual threads in improving Java's multiprocessing capabilities. This talk will provide a comprehensive overview of the topic, highlighting the benefits and takeaways for attendees. Speaker: Liliia Rafikova, Software Developer, Amazon Web Services Talk: Part 2 of the Deep Dive: Advanced Java Concurrency Advanced Locking Mechanisms Explore beyond basic synchronized blocks: understand ReentrantReadWriteLock and StampedLock for fine-grained concurrency. Learn how to optimize read/write operations, reduce contention, and achieve more predictable performance under heavy load. CompletableFuture and Asynchronous Programming Move from basic futures to CompletableFuture and unlock powerful patterns like chaining, combining, and composing tasks. Discover best practices for error handling, debugging asynchronous flows, and integrating with modern reactive streams (Flow API). Performance Considerations and Tuning Identify bottlenecks such as lock contention and thread starvation. Use tools like Java Flight Recorder, Mission Control, and enhanced garbage collectors (G1, ZGC) to profile, monitor, and fine-tune your applications for maximum throughput and minimal latency. Advanced Topics (Optional) Memory Model & Happens-Before Relationship: Understand the Java Memory Model’s guarantees and how they ensure thread-safe operations. Custom Synchronizers: Learn how to build specialized concurrency constructs using AbstractQueuedSynchronizer. Java Concurrency Enhancements in Recent Versions: Stay current with new features like VarHandle, enhancements to CompletableFuture, and upcoming trends (e.g., Project Loom’s virtual threads). Speaker biogs: Liliia Rafikova, Software Developer, Amazon Web Services I'm an experienced backend software engineer. Having over 10+ years of industry experience with the last 5 years I work on building scalable, highly-available and low latency distributed systems. Main stack: Kafka, Java 17, Rust, AWS Services, SQL/NoSQL databases, Docker Salman Shah, Senior Software Engineer, Smartsheet Traveller, Speaker, Engineer simplifying technology. Build, Value, Repeat. This event is organised by RecWorks on behalf of the London Java Community. The London Java Community is sponsored by Hazelcast, Vonage, Neo4j, and Discover

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Our Initiatives

The LJC has many initiatives, all volunteer lead and founded by our organisers and members. Read about our initiatives below.

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Eclipse Foundation

The Eclipse Foundation is a non-profit organisation that supports open source software development. It provides a place for developers to collaborate on and innovate open source projects. The Eclipse Foundation also provides services to the Eclipse community, such as IP management, ecosystem development, and marketing.

Adopt a JSR

The LJC has a seat on the JCP and runs the Adopt a JSR programme for Java SE (at OpenJDK), Java ME and Java EE (now Jakarta EE).

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Adoptium

The LJC works on OpenJDK, and co-founded Eclipse Adoptium (the successor to AdoptOpenJDK), the world’s leading FREE OpenJDK distribution!

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Microprofile

The LJC is a founding member of microprofile.io –
a new community around building a defacto set of API’s and implementations for Microservices in Java.

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Jakarta EE / EE4J

The LJC is a founding member of Jakarta EE / EE4J – the new home for Java EE at the Eclipse Foundation.

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Sponsor the LJC

The LJC has a multitude of events and global initiatives impacting hundreds of thousands of developers due to the generosity of Recworks, volunteers and key sponsors. You can donate directly or talk to us about a sponsorship package.

Talk to us on Slack

Our LJC Slack group is a vibrant real time community where you can speak with your fellow technologists and world leading experts about topics that matter to you!

Since it’s inception, RecWorks have always invested in and sponsored the London Java Community both in terms of time and money to power the events. Over the years that relationship has now become more official in that for any placement which came through an LJC event, RecWorks now gives a % of all the placements back to the community. 

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