如何在 Java 8 中映射映射中的值？
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How to map values in a map in Java 8?
提问by siledh
Say I have a Map<String, Integer>. Is there an easy way to get a Map<String, String>from it?
说我有一个Map<String, Integer>. 有没有一种简单的方法可以从中获取Map<String, String>？
By easy, I mean not like this:
简单，我的意思不是这样：
Map<String, String> mapped = new HashMap<>();
for(String key : originalMap.keySet()) {
mapped.put(key, originalMap.get(key).toString());
}
But rather some one liner like:
而是一些像这样的班轮：
Map<String, String> mapped = originalMap.mapValues(v -> v.toString());
But obviously there is no method mapValues.
但显然没有办法mapValues。
采纳答案by assylias
You need to stream the entries and collect them in a new map:
您需要流式传输条目并将它们收集在新地图中：
Map<String, String> result = map.entrySet().stream()
.collect(Collectors.toMap(Entry::getKey, e -> String.valueOf(e.getValue()));
回答by skiwi
The easiest way to do so is:
最简单的方法是：
Map<String, Integer> map = new HashMap<>();
Map<String, String> mapped = map.entrySet().stream()
.collect(Collectors.toMap(Map.Entry::getKey, entry -> String.valueOf(entry.getValue())));
What you do here, is:
你在这里做的是：
- Obtain a
Stream<Map.Entry<String, Integer>> - Collect the results in the resulting map:
- Map the entries to their key.
- Map the entries to the new values, incorporating
String.valueOf.
- 获得一个
Stream<Map.Entry<String, Integer>> - 在生成的地图中收集结果：
- 将条目映射到它们的键。
- 将条目映射到新值，将
String.valueOf.
The reason you cannot do it in a one-liner, is because the Mapinterface does not offer such, the closest you can get to that is map.replaceAll, but that method dictates that the type should remain the same.
您不能在单行中执行此操作的原因是因为该Map接口不提供此类，您可以获得的最接近的是map.replaceAll，但该方法规定类型应保持不变。
