Java Thread Dump: Capture with jcmd, jstack and Analyze It
Capture a Java thread dump with jcmd, jstack, kill -3 or JSON for virtual threads, read every line and find deadlocks, CPU hogs and stuck pools.
Java Concurrency Interview Questions
Java concurrency interview guide lists frequently asked questions for beginners and experienced programmers to help refresh multi-threading concepts.
Java volatile Keyword: Thread Safety, Visibility and Atomicity
The Java volatile keyword makes writes visible to other threads but does not make count++ atomic. See happens-before, stop flags and lazy singletons.
Are Local Variables Thread Safe in Java? Stack vs Heap
Are local variables thread safe in Java? Yes, each thread keeps its own stack copy. See when shared objects, lambdas and escaping references break it.
Runnable vs Callable in Java: Differences With Examples
Runnable vs Callable in Java explained with examples of return values, checked exceptions, Future, FutureTask, invokeAll and the Java 19 Future methods.
Daemon Thread in Java: JVM Exit Rules and Examples
Learn what a daemon thread in Java is, how setDaemon() works, why the JVM does not wait for it, virtual threads, executors and when to use one.
Semaphore vs ReentrantLock in Java: Key Differences
Semaphore vs ReentrantLock in Java compared with a table and code for ownership, reentrancy, IllegalMonitorStateException, conditions and when to use each.
IllegalMonitorStateException in Java: Causes and Fixes
IllegalMonitorStateException in Java explained, with every cause from wait() and notify() outside synchronized to ReentrantLock unlock() and the fixes.
Java Thread join(): Timeouts, Interrupts and join vs yield
Java thread join() waits for another thread to finish. Learn join(long), join(Duration), interrupts, deadlocks, visibility and yield() vs join().
Java Concurrency Guide: Threads, Executors and Virtual Threads
Java concurrency explained for Java 25 with thread safety, a race condition fix, a timeline from Java 1.0 to 25 and all our tutorials grouped by task.
How to Kill a Thread in Java: interrupt(), Flags, Thread.stop
How to kill a thread in Java safely with interrupt() or a volatile flag, why Thread.stop() throws UnsupportedOperationException and how to stop tasks.
Thread Name in Java: Set and Get the Name of a Thread
Set and get the thread name in Java with getName(), setName(), constructors and Thread builders, default names, executor thread names and threadId().
Java Structured Concurrency with StructuredTaskScope (Java 25)
Java structured concurrency with the Java 25 preview API. Learn StructuredTaskScope.open(), fork, join, Joiners, timeouts, custom joiners and the flags.
Java Virtual Threads Guide with Examples (Java 25)
Java virtual threads explained for Java 25 with examples, carrier threads, the Java 24 pinning fix, when not to use them, pooling and ThreadLocal pitfalls.
Java DelayQueue Tutorial with Delayed Element Examples
Java DelayQueue explained with a Delayed record, take(), poll() and peek() rules, a producer-consumer order timeout example and the alternatives.
Java ExecutorService Shutdown: shutdown() vs shutdownNow()
Shut down a Java ExecutorService with shutdown(), awaitTermination() and shutdownNow(), or with try-with-resources and close() on Java 19+. Covers queued tasks, RejectedExecutionException, virtual threads, JVM exit and shutdown hooks.
Cancel a Task in ExecutorService With Future.cancel()
Learn to cancel a task in ExecutorService with Future.cancel(), stop running tasks with interrupts, cancel after a timeout and clean up with purge().
Java ScheduledExecutorService: Fixed Rate vs Fixed Delay
Java ScheduledExecutorService examples for delayed and periodic tasks, scheduleAtFixedRate vs scheduleWithFixedDelay, exceptions, cancel and daily jobs.
Java ExecutorService invokeAll() and invokeAny() with Examples
Learn how ExecutorService invokeAll() runs a batch of Callable tasks, with timeouts, failed tasks, Future.state() and invokeAny() for the first result.
RejectedExecutionHandler in Java: Policies and Examples
A RejectedExecutionHandler decides what happens to a task that a ThreadPoolExecutor cannot accept. Compare the four built-in policies with real output and write custom handlers.
ExecutorService in Java: Guide With Java 25 Examples
Learn ExecutorService in Java with Java 25 examples for submit(), invokeAll(), Future results, close() with try-with-resources and virtual threads.
Java AtomicInteger Tutorial: Methods, CAS and LongAdder
AtomicInteger lets many threads update one int without a lock. Covers every method with results, compare-and-swap, AtomicInteger vs synchronized vs volatile, and LongAdder for high contention.
Java Hashtable: Why It Is Legacy and What to Use Instead
Java Hashtable is a synchronized legacy map. See how it works, why compound updates still race, HashMap vs Hashtable, and when to use ConcurrentHashMap.
Producer Consumer Problem in Java Using BlockingQueue
Solve the producer consumer problem in Java with BlockingQueue, put() and take(), a poison pill per consumer, timeouts and virtual threads.
Thread Life Cycle in Java: 6 Thread States With Examples
Learn the thread life cycle in Java with all six Thread.State values, a state diagram, runnable demos, transitions, virtual threads and thread dumps.
Concurrency vs Parallelism in Java with Examples
Concurrency vs parallelism explained with Java 25 examples, a timeline diagram, the four combinations and which Java API fits waiting or CPU-bound tasks.
Java Callable and Future Tutorial with Examples (Java 25)
Callable and Future in Java with runnable examples of get() with timeout, exceptions, cancel(), Java 19 state() and resultNow(), and FutureTask.
Java Thread Pool: ThreadPoolExecutor and Fixed Pools
Java thread pool guide with Executors factory pools, a fixed size pool example, ThreadPoolExecutor settings, pool sizing, monitoring and virtual threads.
Java ConcurrentLinkedDeque: Non-blocking Thread-safe Deque
Learn how Java ConcurrentLinkedDeque works, with lock-free methods for both ends, a 100-thread example, size() limits, work stealing and deque comparison.
Java Semaphore: acquire(), release(), tryAcquire() Examples
Java Semaphore explained with examples for acquire(), release(), tryAcquire() timeouts, fairness, throttling an executor and limiting virtual threads.
Java wait(), notify() and notifyAll(): Producer Consumer Guide
Java wait notify explained with wait(), notify() and notifyAll(), a bounded producer consumer queue, spurious wakeups and BlockingQueue.
Java Binary Semaphore vs Mutex (with Examples)
A Java binary semaphore is a Semaphore(1). Learn how it works, when to use it, how it differs from a mutex, signaling and the over-release bug.
Java Lock and ReentrantLock Tutorial with Examples
Use a Java Lock to let one thread at a time change shared data. Covers ReentrantLock with try-finally, tryLock() with a timeout, fair locks, ReadWriteLock, StampedLock, Condition and virtual threads.
Java ThreadLocal: When and How to Use It (With Examples)
Learn when to use Java ThreadLocal, why it leaks in thread pools, how remove() in finally fixes it, and when Java 25 ScopedValue is the better choice.
Java UncaughtExceptionHandler: Log and Restart Failed Threads
Use Java UncaughtExceptionHandler to log thread failures, restart threads with a limit, and see why ExecutorService submit() never reaches the handler.
Java Compare and Swap (CAS): How It Works With Examples
Compare and swap (CAS) writes a new value only if a variable still holds the value we read. Learn compareAndSet(), CAS loops, VarHandle and the ABA problem in Java 25.
Java CountDownLatch Example: await(), countDown() and Timeout
Java CountDownLatch example with await(), countDown() in finally, timeouts, a starting gate for tests and a comparison with CyclicBarrier and invokeAll.
Runnable vs Thread in Java: Differences and When to Use Each
Runnable vs Thread in Java compared with examples, a difference table, shared tasks, executors and virtual threads, and when extending Thread still fits.
Sleep vs Wait in Java: Lock, State and Wake-Up Differences
Sleep vs wait in Java compared with Java 25 examples, covering which method keeps the lock, the thread states, wake-up rules and modern alternatives.
Object Level Lock vs Class Level Lock in Java
Object level lock vs class level lock in Java with runnable proof that the two locks are independent, syntax variants, pitfalls and virtual thread notes.
ThreadPoolExecutor BlockingQueue: Queue Choice and Sizing
See how the ThreadPoolExecutor BlockingQueue decides when the pool grows, with SynchronousQueue, bounded and priority queues, sizing and rejected tasks.
Deadlock in Java: Create, Detect and Resolve It
Deadlock in Java explained with a deterministic example, jstack and ThreadMXBean detection, lock ordering, tryLock timeouts and interruptible recovery.