想要一个代码来实现synchronized和asynchronized方法之间的区别

Question

我试图设置同步和非同步方法之间的区别..我试过以下代码

 class Counter {
    private int counter = 10;
    public int getCounter() {
        return counter;
    }

    public synchronized void doIncrementAndDecrement() {
        counter++;
        keepBusy(500);
        counter--;
    }

    public void keepBusy(int howLong) { // (D)
        long curr = System.currentTimeMillis();
        while (System.currentTimeMillis() < curr + howLong)
            ;
    }
}

class MyCounterThread extends Thread {

    Counter c;

    public MyCounterThread(Counter c, String name) {
        // TODO Auto-generated constructor stub
        super(name);
        this.c = c;
        start();
    }

    @Override
    public void run() {
        for (;;) {
            c.doIncrementAndDecrement();
            sleepForSometime();
            System.out.println(c.getCounter());
        }
    }

    public void sleepForSometime() { // (D)
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class UnSynchronizedExapmle {

    public static void main(String[] args) throws InterruptedException {
        Counter c = new Counter();
        MyCounterThread t1 = new MyCounterThread(c, "A");
        MyCounterThread t2 = new MyCounterThread(c, "B");
        MyCounterThread t3 = new MyCounterThread(c, "C");
    }
}

所以上面我有doIncrementAndDecrement()同步方法..

所以我期望计数器的价值每次都应该是10.但这不会发生我有输出就好

10
10
11
10
10
10
10
11
10
10
11
10
11
11
10
10
11
10
11
10
10
10
11
10
10
11
10

所以,请帮助我为什么会发生这种情况..或者任何博客/文章,用于解释同步和异步方法之间的区别

Answer 1

您的getCounter()方法未同步.因此,即使一个线程可能正在锁定该方法,另一个线程仍然可以访问并打印您的计数器变量