检查“get"链要求为空

问题描述

假设我想执行以下命令:

Let's say I'd like to perform the following command:

house.getFloor(0).getWall(WEST).getDoor().getDoorknob();

为了避免 NullPointerException，如果出现以下情况，我必须执行以下操作:

To avoid a NullPointerException, I'd have to do the following if:

if (house != null && house.getFloor(0) && house.getFloor(0).getWall(WEST) != null
  && house.getFloor(0).getWall(WEST).getDoor() != null) ...

有没有一种方法或者一个已经存在的 Utils 类可以更优雅地做到这一点，让我们说一下类似下面的内容?

Is there a way or an already existing Utils class that does this more elegantly, let's say something like the following?

checkForNull(house.getFloor(0).getWall(WEST).getDoor().getDoorknob());

推荐答案

最好的方法是避免链条.如果您不熟悉迪米特法则 (LoD)，我认为您应该这样做.您已经给出了一个完美的消息链示例，该消息链与它不了解的类过于密切.

The best way would be to avoid the chain. If you aren't familiar with the Law of Demeter (LoD), in my opinion you should. You've given a perfect example of a message chain that is overly intimate with classes that it has no business knowing anything about.

德米特法则:http://en.wikipedia.org/wiki/Law_of_Demeter

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