番石榴：为什么没有Lists.filter（）函数？ [英] Guava: Why is there no Lists.filter() function?

问题描述

是否有一个原因是
$ b $ pre $ Lists.transform（）


但是没有

$ p $ Lists.filter（）


？

如何正确过滤列表？我可以使用

  new ArrayList（Collection2.filter（））
  

当然，但是这样做并不能保证我的排序保持不变，如果我理解正确的话。

解决方案

它没有实现，因为它会在返回的列表视图（邀请性能错误）上暴露大量的慢方法，例如#get（index）。而ListIterator也会很难实现（尽管我提交了一个补丁

由于索引方法在过滤的List视图中效率不高，最好使用过滤后的Iterable，而不是Iterable有他们。

Is there a reason there's

Lists.transform()

but no

Lists.filter()

?

How do I filter a list correctly? I could use

new ArrayList(Collection2.filter())

of course, but this way it's not guaranteed that my ordering stays the same, if I understand correctly.

解决方案

It wasn't implemented because it would expose a perilous large number of slow methods, such as #get(index) on the returned List view (inviting performance bugs). And ListIterator would be a pain to implement as well (though I submitted a patch years ago to cover that).

Since indexed methods can't be efficient in the filtered List view, it's better to just go with a filtered Iterable, which doesn't have them.

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