Synchronized和ReentrantLock的区别

• synchronize是关键字，属于JVM层面；ReentrantLock是具体的类，是API层面的锁
• synchronize不需要用户手动释放；ReentrantLock需要手动释放
• synchronize不可以被中断；ReentrantLock可以被中断
• synchronize是非公平锁；ReentrantLock 默认非公平锁，构建函数传入boolean值，true为公平锁，false为非公平锁。
• synchronize要么随机唤醒一个要么全部唤醒；ReentrantLock 用来实现需要分组唤醒需要唤醒的线程们，可以精确唤醒。

condition实现精确唤醒：

public class SynAndReetrantLockDemo {

    static class ShareResource{
        private int number = 1; //A=1;B=2;C=3
        private Lock lock = new ReentrantLock();
        private Condition condition1 = lock.newCondition();
        private Condition condition2 = lock.newCondition();
        private Condition condition3 = lock.newCondition();

        public void print5() {
            try {
                lock.lock();
                //1.判断
                while (number != 1) {
                    condition1.await();
                }
                //2.干活
                for (int i = 1; i <= 5; i++) {
                    System.out.println(Thread.currentThread().getName() + "\t" + i);
                    Thread.sleep(200);
                }
                //3.通知
                number = 2;
                condition2.signal();
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        }


    public void print10() {
        try {
            lock.lock();
            //1.判断
            while (number != 2) {
                condition2.await();
            }
            //2.干活
            for (int i = 1; i <= 10; i++) {
                System.out.println(Thread.currentThread().getName() + "\t" + i);
                Thread.sleep(200);
            }
            //3.通知
            number = 3;
            condition3.signal();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }


    public void print15() {
        try {
            lock.lock();
            //1.判断
            while (number != 3) {
                condition3.await();
            }
            //2.干活
            for (int i = 1; i <= 15; i++) {
                System.out.println(Thread.currentThread().getName() + "\t" + i);
                Thread.sleep(200);
            }
            //3.通知
            number = 1;
            condition1.signal();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}
    public static void main(String[] args) {
        ShareResource shareResource = new ShareResource();

        new Thread(()->{
            for (int i = 1; i <= 10; i++) {
                shareResource.print5();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 1; i <= 10; i++) {
                shareResource.print10();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 1; i <= 10; i++) {
                shareResource.print15();
            }
        },"C").start();
        }
    }