线程锁synchronized锁定的细节

/**
 * Created by suomali on 2019/6/18.
 *
 * syn的锁定  方法锁  和块锁this差不多
 * syn锁定范围   太大容易拖慢效率  小了容易锁定失败
 */
public class TrainBF2 {
    public static void main(String[] args) {
        SynTrain12306 synTrain = new SynTrain12306();
        new Thread(synTrain,"小胡").start();
        new Thread(synTrain,"小高").start();
    }
}

class SynTrain12306 implements Runnable{

    private Integer Tickets = 4;
    private boolean flag = true;

    @Override
    public void run() {
        while(flag){
            test3();
        }
    }

    public void test3(){ //双重check
        if (Tickets <= 0) { //处理没票时的情况 如果没票了就都不用等了
            flag = false;
            return;
        }
        synchronized (this) {
            if (Tickets <= 0) { //处理只剩下一张票的情况 都等在外边 但是当最后一张票被购买时就都不等了
                flag = false;
                return;
            }
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "买到了票,还有" + --Tickets + "张票");
        }
    }


    public void test2(){
        synchronized (this) { //锁定面积大的块
            if (Tickets <= 0) {
                flag = false;
                return;
            }
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"买到了票,还有"+ --Tickets +"张票");
        }

    }
    //直接锁定方法   使用这个方法的线程都需要等待
    public synchronized void test(){
        if(Tickets == 0){
            flag = false;
            return;
        }
        try {
            Thread.sleep(200);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()+"买到了票,还有"+ --Tickets +"张票");
    }
}