Java多线程问题。生产者（P）生产一个产品，消费者（C）获取一个产品；P没有生产产品之前，C不能够获取；P只能够在C获取产品之后，才能生产下一个。-Java multi-threading issues. Producer (P) production of a product, consumers (C) to obtain a product　P does not produce products before, C can not access　P can only obtain the product in C, to produce the next.