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

class Demo {
    private int i = 100;

    int setI(int y) {
        System.out.println("减去" + y);
        return i = i - y;
    }

    int getI() {
        return i;
    }

}

public class SynchronrizedTest implements Runnable {
    Lock lock = new ReentrantLock();
    private Demo demo = new Demo();

    public static void main(String[] args) {

        SynchronrizedTest test1 = new SynchronrizedTest();

        Thread thread1 = new Thread(test1, "线程1");
        Thread thread2 = new Thread(test1, "线程2");
        thread1.start();
        thread2.start();

    }

    public void run() {
        for (int i = 0; i < 5; i++) {
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.lock();
            System.out.println(Thread.currentThread().getName() + "操作之前: " + demo.getI());
            this.setI(10);
            System.out.println(Thread.currentThread().getName() + "操作之后: " + demo.getI());
            System.out.println();
            lock.unlock();
        }
    }

    int setI(int y) {
        return demo.setI(y);
    }

}

------解决方案--------------------

探讨

有木有这种情况，a执行完A后，已经释放了A的锁，还未获得B的锁，但是b线程获得了A的锁，当b释放A的锁时，a获得了B的锁，此时数据依然被a修改过了，这种问题怎么解决呢？