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JavaIntermediate#concurrency
JavaAdvanced#concurrency
What is a ThreadLocal and when would you use it?
ThreadLocal provides a variable with a separate copy for each thread accessing it, useful for per-thread context like database connections, user sessions, or date formatters without synchronization overhead.
Example
ThreadLocal<SimpleDateFormat> formatter = ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyy-MM-dd"));
formatter.get().format(new Date());