What is the purpose of the ReentrantLock class in Java and how does it compare to synchronized?

The ReentrantLock class in Java is used to control access to shared resources in a multithreaded environment, providing a lock mechanism with reentrant capability. This means that a thread that already holds the lock can acquire it again without deadlocking.

Advantages of ReentrantLock compared to the synchronized keyword:

• Flexibility in lock management: you can explicitly acquire and release the lock, allowing for more complex synchronization scenarios.
• Ability to interrupt waiting for the lock: the lockInterruptibly() method allows a thread to be interrupted while waiting for the lock.
• Attempt to acquire the lock without waiting: the tryLock() method attempts to acquire the lock and immediately returns a result, without blocking the thread.
• Support for conditions (Condition): ReentrantLock provides Condition objects for more fine-grained waiting and notification, unlike wait()/notify() in synchronized.

Example of using ReentrantLock:

import java.util.concurrent.locks.ReentrantLock;

public class Counter {
    private final ReentrantLock lock = new ReentrantLock();
    private int count = 0;

    public void increment() {
        lock.lock();
        try {
            count++;
        } finally {
            lock.unlock();
        }
    }

    public int getCount() {
        lock.lock();
        try {
            return count;
        } finally {
            lock.unlock();
        }
    }
}