在 Java 中，Lock 接口和 ReentrantLock 类提供了比使用 synchronized 方法和代码块更广泛的锁定机制。


简单示例：

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockExample {
    private final Lock lock = new ReentrantLock();
    private int counter = 0;

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

    public int getCounter() {
        lock.lock();
        try {
            return counter;
        } finally {
            lock.unlock();
        }
    }

    public static void main(String[] args) {
        ReentrantLockExample example = new ReentrantLockExample();
        example.increment();
        System.out.println("Counter: " + example.getCounter());
    }
}

生产者-消费者示例：

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.LinkedList;
import java.util.Queue;

public class ProducerConsumer {

    private final Queue<Integer> queue = new LinkedList<>();
    private final int CAPACITY = 5;
    private final Lock lock = new ReentrantLock();
    private final Condition notFull = lock.newCondition();
    private final Condition notEmpty = lock.newCondition();

    public void produce() throws InterruptedException {
        int value = 0;
        while (true) {
            lock.lock();
            try {
                while (queue.size() == CAPACITY) {
                    notFull.await();
                }
                queue.add(value);
                System.out.println("Produced " + value);
                value++;
                notEmpty.signal();
            } finally {
                lock.unlock();
            }
            Thread.sleep(1000); // Simulate time taken to produce an item
        }
    }

    public void consume() throws InterruptedException {
        while (true) {
            lock.lock();
            try {
                while (queue.isEmpty()) {
                    notEmpty.await();
                }
                int value = queue.poll();
                System.out.println("Consumed " + value);
                notFull.signal();
            } finally {
                lock.unlock();
            }
            Thread.sleep(1500); // Simulate time taken to consume an item
        }
    }

    public static void main(String[] args) {
        ProducerConsumer pc = new ProducerConsumer();

        Thread producerThread = new Thread(() -> {
            try {
                pc.produce();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        });

        Thread consumerThread = new Thread(() -> {
            try {
                pc.consume();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        });

        producerThread.start();
        consumerThread.start();
    }
}