Google馆藏(番石榴库):ImmutableSet/List/Map和Filtering [英] Google Collections (Guava Libraries): ImmutableSet/List/Map and Filtering

问题描述

假定您要构建ImmutableSet/List/Map对象的副本，但要过滤掉一些原始条目.一种实现方法如下:

Assume that you want to build a copy of an ImmutableSet/List/Map object but filter out some of the original entries. One way to implement that is the following:

ImmutableList.copyOf(Iterables.filter(myObject, myObject.EQUALS));

其中，myObject.EQUALS是Iterables.filter()操作的谓词.我认为这是一个非常优雅且易于阅读的实现.但是，一个人构建两个列表对象(第一个通过Iterables.filter(...)调用，第二个通过ImmutableList.copyOf(...)调用)，效率很低.

where myObject.EQUALS is a predicate for the Iterables.filter() operation. I think this is a pretty elegant and easy-to-read implementation. However, one builds two list objects (first through the Iterables.filter(...) call, second through ImmutableList.copyOf(...)) which is very inefficient.

有人知道一种更有效的方法吗?

Does anybody know of a more efficient way to do it?

我猜最好的办法是将过滤谓词添加到ImmutableSet/List/Map生成器，以便对象只能构造一次.但不幸的是，没有这样的参数.

I guess the best thing would be to add filter predicates to the ImmutableSet/List/Map builders so that the object must be constructed only once. But unfortunately there is no such parameter.

推荐答案

Iterables.filter()的结果只是对myObject中数据的查看:新列表仅由ImmutableList.copyOf()使用提供的过滤迭代器构建由Iterable

The result of Iterables.filter() is just a view over the data in myObject: the new list is only built by ImmutableList.copyOf() using the filtering iterator provided by the Iterable

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