检查“获取”链调用null [英] Check chains of "get" calls for null

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) ...

有没有一种方法或已经存在的Utils类更优雅地做到这一点，让我们说下面的内容？

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

最好的办法是避免链条。如果您不熟悉得墨忒耳法（LoD），我认为您应该这样做。你已经给出了一个完美的消息链示例，它与那些没有业务知识的类过于亲密。

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.

得墨忒耳定律： http://en.wikipedia.org/wiki/Law_of_Demeter

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