Learn how to use Java's synchronized keyword correctly — with real payment and banking examples covering race conditions, synchronized methods, blocks, deadlock-free transfers, double-checked locking, and virtual thread pitfalls. Covers Java 8 through 21
Learn how to use Java's CompletableFuture for async programming — with real payment pipeline examples covering supplyAsync, thenCompose, thenCombine, error handling, and custom thread pools. Covers Java 8, 9, and 21.
A switch on a null String, enum, Integer or sealed type throws NullPointerException, and default won't catch it. Why, how 8 to 25 differ, and the fix.
Learn how to use Java's ScheduledExecutorService for periodic tasks — with real Kafka and payment pipeline examples covering scheduleAtFixedRate, scheduleWithFixedDelay, exception handling, graceful shutdown, and virtual threads. Covers Java 8 through 21.
Method.invoke wraps everything its target throws in an InvocationTargetException with no message. Here's how to see the real cause, on JDK 8 through 25.
A ThreadLocal that worked fine in a thread pool returns null the moment a virtual thread forks a subtask. Here's the mechanism, and what actually fixes it.
Virtual threads pinned by synchronized collapse throughput to your CPU count and can hang outright. Diagnose pinning on JDK 21 and fix it on 24+.
InvalidClassException: local class incompatible means the stream's serialVersionUID no longer matches your class. Here is why it drifted, and how to fix it without losing data.
Flink throws ValidationException: Could not find any factory for identifier 'kafka' in the classpath. Here is why SPI discovery fails and how to fix it.
NoClassDefFoundError and ClassNotFoundException look interchangeable and are not. Read the frames, find the real cause, and stop the repeat throws.