多线程bug修复

public class ThreadDemo {
    public static void main(String[] args) {
        ThreadTest test = new ThreadTest();
        new Thread(test).start();
        new Thread(test).start();
        new Thread(test).start();
        new Thread(test).start();
    }
}

class ThreadTest implements Runnable {
    private volatile int count = 10;

    public void run() {

        while (count > 0) {
            synchronized (this) {
                System.out.println(Thread.currentThread().getName() + "   "
                        + count--);
            }
        }

    }
}

Thread-0 10
Thread-3 9
Thread-3 8
Thread-3 7
Thread-3 6
Thread-3 5
Thread-3 4
Thread-3 3
Thread-3 2
Thread-3 1
Thread-2 0
Thread-1 -1
Thread-0 -2

修正案：

public class ThreadDemo {
    public static void main(String[] args) {
        ThreadTest test = new ThreadTest();
        new Thread(test).start();
        new Thread(test).start();
        new Thread(test).start();
        new Thread(test).start();
    }
}

class ThreadTest implements Runnable {
    private volatile int count = 10;

    public void run() {

        while (count > 0) {
            synchronized (this) {
                if (count > 0) {
                    System.out.println(Thread.currentThread().getName() + "   "
                            + count--);
                }
            }
        }

    }
}

Thread-0 10
Thread-1 9
Thread-1 8
Thread-1 7
Thread-1 6
Thread-0 5
Thread-0 4
Thread-0 3
Thread-0 2
Thread-0 1