在程序Multi -Threading java中获得不一致/错误的输出

Question

/*
This should always produce 0 as output since all three methods increment(), decrement(), value()  are thread safe(synchronized).  but it is returning 1
*/

class Counter implements Runnable {
    private int c = 0;

    public  synchronized void increment() {
        c++;
    }
    public synchronized void decrement() {
        c--;
    }
    public synchronized int value() {
        return c;
    }
    public void run() {
        try {
            this.increment();
            Thread.sleep(1000);
            this.decrement();
            Thread.sleep(1000);
            this.increment();
            Thread.sleep(1000);
            this.decrement();
            Thread.sleep(1000);
        }
        catch (InterruptedException e){
            return;
        }
    }
    public static void main(String args[]) throws InterruptedException {
       Counter c =  new Counter();
       new Thread(c).start();
       new Thread(c).start();
       System.out.println(c.value());
    }

}

Answer 1

像其他人一样,你需要确保踏板已经完成执行,为此你需要调用join.例如

public static void main(String args[]) throws InterruptedException {
   Counter c =  new Counter();
   Thread t1 = new Thread(c).start();
   Thread t2 = new Thread(c).start();
   t1.join();
   t2.join();
   System.out.println(c.value());
}

应该正确运行