Have you had to use classes from java.util.concurrent?

Yes, in my practice I often used classes from the java.util.concurrent package to solve problems related to multithreading and synchronization.

For example:

• ExecutorService for managing thread pools and asynchronous task execution.
• ConcurrentHashMap for thread-safe access to collections without locks.
• CountDownLatch and CyclicBarrier for thread coordination.
• Semaphore for limiting the number of operations performed simultaneously.

Example of using ExecutorService:

ExecutorService executor = Executors.newFixedThreadPool(5);
for (int i = 0; i < 10; i++) {
    int taskId = i;
    executor.submit(() -> {
        System.out.println("Task " + taskId + " is running");
    });
}
executor.shutdown();

Using these classes allows writing efficient, scalable, and safe code in a multithreaded environment.