Java8:哈希映射<X，Y>到HashMap<X，Z>使用 Stream/Map-Reduce/Collector [英] Java8: HashMap<X, Y> to HashMap<X, Z> using Stream / Map-Reduce / Collector

问题描述

我知道如何转变"；Y 的简单 Java List ->Z，即:

I know how to "transform" a simple Java List from Y -> Z, i.e.:

List<String> x;
List<Integer> y = x.stream()
        .map(s -> Integer.parseInt(s))
        .collect(Collectors.toList());

现在我想对地图做基本相同的事情，即:

Now I'd like to do basically the same with a Map, i.e.:

INPUT:
{
  "key1" -> "41",    // "41" and "42"
  "key2" -> "42"      // are Strings
}

OUTPUT:
{
  "key1" -> 41,      // 41 and 42
  "key2" -> 42       // are Integers
}

解决方案不应仅限于String ->整数.就像上面的 List 示例一样，我想调用任何方法(或构造函数).

The solution should not be limited to String -> Integer. Just like in the List example above, I'd like to call any method (or constructor).

推荐答案

Map<String, String> x;
Map<String, Integer> y =
    x.entrySet().stream()
        .collect(Collectors.toMap(
            e -> e.getKey(),
            e -> Integer.parseInt(e.getValue())
        ));

它不如列表代码那么好.您不能在 map() 调用中构造新的 Map.Entry，因此工作会混入 collect() 调用中.

It's not quite as nice as the list code. You can't construct new Map.Entrys in a map() call so the work is mixed into the collect() call.

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