Java Concurrency Explained: Key Concepts from Threads to CAS and JMM

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A technical guide published on DEV Community covers 40 Java concurrency and multithreading interview topics in depth. It explains the difference between processes and threads, highlighting how Java 21's virtual threads via Project Loom allow millions of lightweight threads without the overhead of platform threads. The guide details the Java Memory Model, clarifying how happens-before relationships, volatile fields, and synchronized blocks ensure visibility and ordering across threads. It also contrasts synchronized with ReentrantLock, and explains why volatile alone is insufficient for compound operations like increment, making AtomicInteger a safer choice. Additionally, it covers how modern ConcurrentHashMap achieves high concurrency through per-bin locking and lock-free reads, unlike the fully synchronized Hashtable.

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