8 sychronized和Lock有什么区别

原始构成

sychronized是关键字属于JVM层面

Monitorenter（底层是通过monitor对象来完成，其实wait/notify等方法也依赖于monitor对象只有在同步块或者方法中才能调用wait/notify等方法）

Monitorexit

Lock是具体的类（java.util.concurrent.locks.Lock）是API层面的锁

使用的方法

Synchronized 不需要用户去手动释放锁，当sychronized代码执行完后系统会自动让线程释放对锁的占用

ReentrantLock则需要用户去手动释放锁若没有主动释放锁，就有可能出现死锁现象。

需要lock() 和unclock() 方法配合try/finally语句来完成

等待是否可中断

sychronized不可中断，除非抛出异常或者正常运行完成

ReentrantLock可中断， 1.设置超时方法 tryLock(long timeout,TimeUnit unit)

​ 2. lockInterruptibly()放代码块中，调用interrupt（）方法可中断

加锁是否公平

Sychronized 非公平锁

ReentrantLock两者都可以，默认非公平锁，构造方法可以传入blooean值，true为公平锁，false为非公平锁

锁绑定多个条件condition

sychronized没有

ReentrantLock用来实现分组唤醒需要唤醒的线程们，可以精确唤醒，而不是像synchronized要么随机唤醒一个线程要么唤醒全部线程。

class ShareResource{

    public volatile int number=1;
    private final Lock lock = new ReentrantLock();
    private final Condition c1 = lock.newCondition();
    private final Condition c2 = lock.newCondition();
    private final Condition c3 = lock.newCondition();


    public void print(int number, int printNumber){
        Condition condition;
        lock.lock();
        try{
            if (number == 1){
                condition = c1;
            }else if (number == 2){
                condition = c2;
            }else{
                condition = c3;
            }
            
            while (number != this.number) {
                condition.await();
            }

            for (int i = 0; i < printNumber; i++) {
                System.out.println(Thread.currentThread().getName()+" "+(i+1));
            }
            condition.signal();
        }catch (Exception ignored){
        }finally {
            lock.unlock();
        }
    }
}

public class ConditionDemo {

    public static void main(String[] args) {
        ShareResource shareResource = new ShareResource();
        new Thread(()->{
            shareResource.number = 1;
            shareResource.print(1,5);
        },"AA").start();
        new Thread(()->{
            shareResource.number = 2;
            shareResource.print(2,10);
        },"BB").start();
        new Thread(()->{
            shareResource.number = 3;
            shareResource.print(3,15);
        },"CC").start();
    }

}