目前我正在学习死锁，我发现了一个死锁的例子，但我不知道死锁是如何在这个例子中发生的。

public class Main {

    public static void main(String[] args) {
        final PolitePerson jane = new PolitePerson("Jane");
        final PolitePerson john = new PolitePerson("John");

        new Thread(new Runnable() {
            @Override
            public void run() {
                 jane.sayHello(john);
            }
        }).start();

       new Thread(new Runnable() {
            @Override
            public void run() {
                john.sayHello(jane);
            }
        }).start();
    }

    static class PolitePerson {
        private final String name;

        public PolitePerson(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }

        public synchronized void sayHello(PolitePerson person){
            System.out.format("%s: %s" + " has said hello to me!%n", this.name, person.getName());

            person.sayHelloBack(this);
        }

        public synchronized void sayHelloBack(PolitePerson person) {
            System.out.format("%s: %s" + " has said hello back to me!%n", this.name, person.getName());
        }
    }
}

我花了一个多小时来了解这里的情况，但没有明白。这是我得到的输出

Jane: John has said hello to me!
John: Jane has said hello to me!

或者我误解了同步。