java Reentrant Lock

//Listing 7-1. Achieving Synchronization in Terms of Reentrant Locks
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

public class A {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(2);
        final ReentrantLock lock = new ReentrantLock();
        class Worker implements Runnable {
            private final String name;

            Worker(String name) {
                this.name = name;
            }

            @Override
            public void run() {
                lock.lock();
                try {
                    if (lock.isHeldByCurrentThread())
                        System.out.printf(
                                "Thread %s entered critical section.%n", name);
                    System.out.printf("Thread %s performing work.%n", name);
                    try {
                        Thread.sleep(2000);
                    } catch (InterruptedException ie) {
                        ie.printStackTrace();
                    }
                    System.out.printf("Thread %s finished working.%n", name);
                } finally {
                    lock.unlock();
                }
            }
        }
        executor.execute(new Worker("ThdA"));
        executor.execute(new Worker("ThdB"));
        try {
            executor.awaitTermination(5, TimeUnit.SECONDS);
        } catch (InterruptedException ie) {
            ie.printStackTrace();
        }
        executor.shutdownNow();
    }
}