最简单的死锁

package thread;
public class TestThread13 {
    public static void main(String[] args) throws InterruptedException {
        synchronized (TestThread13.class) {
            Thread th = new Thread(new A());
            th.start();
            th.join(100);
            System.out.println("主线程企图进入");
            synchronized(A.class){
                System.out.println("主线程进入了A.class锁");
            }
        }
    }
}
class A implements Runnable{
    @Override
    public void run() {
        synchronized (A.class) {
            System.out.println("副线程企图进入");
            synchronized (TestThread13.class) {
                System.out.println("副线程进入了TestThread13.class锁");
            }
        }
    }
}