最简单的使用信号量吧，Semephore 就可以了，wait, notify 也可以的，你可能不理解这两个方法。notify 调用后并不会释放锁，需要等到 wait 或者 sychronized 结束。下面这段代码就能实现互相等待，输出结果是“1 one 2 two 3 three”
```java
import lombok.extern.slf4j.Slf4j;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@Slf4j
public class DemoApplication implements CommandLineRunner {

Object lock = new Object();

public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}

@Override
public void run(String... args) throws Exception {
System.out.println("1");
new Thread(() -> stop()).start();
pause();
System.out.println("2");
pause();
System.out.println("3");
pause();
}

public void stop() {
System.out.println("one");
pause();
System.out.println("two");
pause();
System.out.println("three");
}

public void pause() {
try {
synchronized (lock) {
lock.notifyAll();
lock.wait();
}
}catch (Exception e) {

}
}
}
```