如何在Java 8 stream forEach中使用if-else逻辑 [英] How to use if-else logic in Java 8 stream forEach

问题描述

我想要做的是在下面的2个流调用中显示。我想根据某些条件将一个集合拆分为两个新集合。理想情况下我想在1中进行。我已经看到了用于.map函数的条件，但找不到forEach的任何内容。实现我想要的最好方法是什么？

What I want to do is shown below in 2 stream calls. I want to split a collection into 2 new collections based on some condition. Ideally I want to do it in 1. I've seen conditions used for the .map function of streams, but couldn't find anything for the forEach. What is the best way to achieve what I want?

    animalMap.entrySet().stream()
            .filter(pair-> pair.getValue() != null)
            .forEach(pair-> myMap.put(pair.getKey(), pair.getValue()));

    animalMap.entrySet().stream()
            .filter(pair-> pair.getValue() == null)
            .forEach(pair-> myList.add(pair.getKey()));

推荐答案

只需将条件放入lambda本身，例如

Just put the condition into the lambda itself, e.g.

animalMap.entrySet().stream()
        .forEach(
                pair -> {
                    if (pair.getValue() != null) {
                        myMap.put(pair.getKey(), pair.getValue());
                    } else {
                        myList.add(pair.getKey());
                    }
                }
        );

当然，这假设两个集合（ myMap 和 myList ）在上面的代码之前声明并初始化。

Of course, this assumes that both collections (myMap and myList) are declared and initialized prior to the above piece of code.

更新：使用 Map.forEach 使代码更短，更有效率和可读性，因为 Jorn Vernee 建议：

Update: using Map.forEach makes the code shorter, plus more efficient and readable, as Jorn Vernee kindly suggested:

    animalMap.forEach(
            (key, value) -> {
                if (value != null) {
                    myMap.put(key, value);
                } else {
                    myList.add(key);
                }
            }
    );

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