多线程同步实现X加减1

多线程同步实现对x加减一的方法

public class SynThreadTest {
    private int x;
    // 设计两个线程，一个对x加1，一个对x减1

    public static void main(String[] args) {
        SynThreadTest stt = new SynThreadTest();
        inc inc =stt.new inc();
        Thread threadA = new Thread(inc);
        threadA.start();

        dec dec = stt.new dec();
        Thread threadB = new Thread(dec);
        threadB.start();
    }

    class inc implements Runnable {
        public void run() {
            for (int i = 0; i < 20; i++) {
                inc();
            }
        }
        private synchronized void inc() {
            x++;
            System.out.println(Thread.currentThread().getName() + "----" + x);
        }
    }

    class dec implements Runnable {
        public void run() {
            for (int i = 0; i < 20; i++) {
                dec();
            }
        }
        private synchronized void dec() {
            x--;
            System.out.println(Thread.currentThread().getName() + "-----"+ x);
        }
    }
}