How can access control be implemented among multiple threads for shared resources?

To manage access to shared resources among multiple threads in Java, synchronization mechanisms are used to prevent race conditions and ensure data correctness.

Main methods:

• synchronized keyword — blocks access to a method or code block, allowing only one thread to execute it at a time.

public synchronized void increment() {
    counter++;
}

• Classes from the java.util.concurrent.locks package, such as ReentrantLock, which provide more flexible control over locks.

ReentrantLock lock = new ReentrantLock();

lock.lock();
try {
    // critical section
} finally {
    lock.unlock();
}

• Use of atomic classes (AtomicInteger, AtomicReference), which provide atomic operations without explicit locks.

• Semaphores, barriers, and other synchronization primitives for more complex scenarios.

The choice of a specific mechanism depends on the task, performance requirements, and synchronization complexity.