This method will return null if the focus owner is not in the same context as the calling thread.

如果该焦点所有者未和调用线程处于同一个上下文中，那么该方法会返回空。

youdao

Or, in the case of a non-applicable method, it becomes a null operation.

或者，在不适用的方法的情况下，成为空操作。

youdao

If the method returns null, it means this is the first time through, so the servlet needs to retrieve the list from the database.

如果方法返回空，意味着这是第一次访问，所以servlet需要从数据库检索列表。

youdao