Essential Knowledge Roadmap for Java Developers After Five Years

JDK Source Code

Understanding JDK source is fundamental; it is divided into collections, concurrent collections, concurrent package, blocking queues, and thread pools.

Collections

Discuss List (ArrayList, Vector, LinkedList, Stack), Set (HashSet, LinkedHashSet, TreeSet), Queue (PriorityQueue, LinkedList, ArrayDeque), Map (HashMap, LinkedHashMap, WeakHashMap, TreeMap) – about 14 commonly used APIs.

Concurrent Collections

Seven main concurrent collections: ConcurrentHashMap, ConcurrentSkipListMap, ConcurrentSkipListSet, CopyOnWriteArrayList, CopyOnWriteArraySet, ConcurrentLinkedQueue, ConcurrentLinkedDeque.

Concurrent Package

Provides core synchronization mechanisms such as AbstractQueuedSynchronizer, Lock, ReentrantLock, ReentrantReadWriteLock, Condition, and utilities like CountDownLatch and CyclicBarrier.

Blocking Queues

Eight common blocking queues are categorized into basic implementations (ArrayBlockingQueue, LinkedBlockingQueue, LinkedBlockingDeque), ordered/delayed implementations (PriorityBlockingQueue, DelayQueue, DelayedWorkQueue), and data‑exchange implementations (SynchronousQueue, LinkedTransferQueue).

Thread Pools

Thread pools rely on the blocking‑queue implementations; understanding their class structure simplifies their use.

JVM Fundamentals

Studying JVM internals helps grasp Java language features (e.g., how boolean is represented) and diagnose runtime problems such as OutOfMemoryError: Java heap space .

Framework Source Code

After mastering JDK and JVM, developers should explore common frameworks in a progressive order: web frameworks (Spring, MyBatis), RPC framework (Dubbo), consistency services (Zookeeper, Eureka), messaging systems (Kafka, RocketMQ), caching, networking (Netty), search (ElasticSearch), and change‑data‑capture tools (Canal, Otter).

Following this roadmap—JDK → JVM → frameworks—allows a five‑year Java developer to build a solid, systematic knowledge base.