java锁Integer等对象失败

public class TestJoin {
    static A testA = new A();
    public volatile static Integer t = 0;

    public static void main(String[] args) throws InterruptedException {
        Thread[] threads = new Thread[10];
        for (int j = 0; j <10; j++) {
            threads[j] = new Thread(testA);
            threads[j].start();
        }
        for (int j = 0; j <10; j++) {
            threads[j].join();
        }
        System.out.println(t);
    }

    static class A implements Runnable {
        @Override
        public void run() {
            for (int f = 0; f <2000; f++) {
                synchronized (t) {
                    t++;
                }
            }
        }
    }

}