HashMap< String，boolean>将所有键复制到HashMap< String，Integer>并将值初始化为零

问题描述

什么是最好的方法?

仅循环遍历并放置密钥和零，或者是否存在另一个更优雅的或现有的库方法.我是否还在使用Google的番石榴Java库，如果它具有任何有用的功能?

Just looping through and putting the key and zero, or is there another more elegant or existing library method. I am also using Google's guava java library if that has any useful functionality ?

想检查是否有类似于列表的复制方法的内容，或Map的 putAll 方法，但仅用于键.

Wanted to check if there was anything similar to the copy method for lists, or Map's putAll method, but just for keys.

推荐答案

不要以为这里有什么花哨的东西:

Don't think there's much need for anything fancy here:

Map<String, Boolean> map = ...;
Map<String, Integer> newMap = Maps.newHashMapWithExpectedSize(map.size());
for (String key : map.keySet()) {
  newMap.put(key, 0);
}

如果您确实想对番石榴感兴趣，可以使用以下选项:

If you do want something fancy with Guava, there is this option:

Map<String, Integer> newMap = Maps.newHashMap(
    Maps.transformValues(map, Functions.constant(0)));

// 1-liner with static imports!
Map<String, Integer> newMap = newHashMap(transformValues(map, constant(0)));

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