我想了解一下最佳实践在这里。它是很好的做法的工厂方法返回null，如果它不能创造什么？这里有一个例子：

I'm wondering about best practice here. Is it good practice for a factory method to return null if it can't create anything? Here's an example:

ICommand command = CommandFactory.CreateCommand(args);
if (command != null)
    command.Execute();
else
    // do something else if there is no command

另一种方法是返回一个 NullCommand 什么的，我猜，但什么是最好的做法？

An alternative would be to return a NullCommand or something, I guess, but what is best practice?

推荐答案

我认为这是可能合理的工厂方法在某些情况下返回null，但是的没有的，如果它是一个名为方法 CreateCommand 。如果是 GetCommand 或 FETCHCOMMAND ，这可能是正确的......但创建方法应该抛出故障异常，我会建议。

I think it's potentially reasonable for a factory method to return null in some situations, but not if it's a method called CreateCommand. If it were GetCommand or FetchCommand, that might be okay... but a Create method should throw an exception on failure, I would suggest.

无论你的真正的希望它返回空在这种情况下当然取决于大局观。 （是否有一个合理的空对象实现，你可以返回来代替，比如？）

Whether you really want it to return null in this situation depends on the bigger picture, of course. (Is there a reasonable null object implementation you could return instead, for example?)