user3768533 user3768533 - 5 months ago 53
Java Question

How to use if-else logic in Java 8 stream forEach

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()));

Answer

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());
                    }
                }
        );

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


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);
                }
            }
    );
Comments