什么时候使用instanceof的正确决策？ [英] When is using instanceof the right decision?

问题描述

正如我一直都明白的那样， instanceof 适用的主要情况是：

As I've always understood it, the main cases where an instanceof is appropriate are:

1. 实现 Object.equals（Object）。所以如果我正在编写一个列表类，并且由于任何原因而不扩展 AbstractList ，我将实现 equals（o）首先测试 o instanceof List ，然后比较元素。


2. A对于不 的特殊情况，重要（算法？）优化可以改变语义，而只改变性能。例如， Collections.binarySearch 对RandomAccess 测试执行实例，并使用稍微不同的二进制搜索 RandomAccess 和非 RandomAccess 列表。



1. Implementing Object.equals(Object). So if I were writing a List class, and not extending AbstractList for whatever reason, I would implement equals(o) by first testing o instanceof List, and then comparing elements.
2. A significant (algorithmic?) optimization for a special case that does not change semantics, but only performance. For example, Collections.binarySearch does an instanceof RandomAccess test, and uses a slightly different binary search for RandomAccess and non-RandomAccess lists.

我不认为 instanceof 表示这两种情况下的代码气味。但是有什么其他情况下使用 instanceof 是明智的吗？

I don't think instanceof represents a code smell in these two cases. But are there any other cases where it is sensible to use instanceof?

推荐答案

p>旧版代码或控件之外的API是 instanceof 的合法用例。 （即使这样，我宁愿在其上写一个OO层，但时间有时排除了这样的重新设计。）

Legacy code or APIs outside of your control are a legitimate use-case for instanceof. (Even then I'd rather write an OO layer over it, but timing sometimes precludes a redesign like that.)

特别是，基于外部类层次结构的工厂似乎是常见用法。

In particular, factories based on external class hierarchies seem a common usage.

这篇关于什么时候使用instanceof的正确决策？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！