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Gunnar Gissel
Gunnar Gissel

Posted on • Updated on • Originally published at gunnargissel.com

Filter Null Values from a List with Java8 Lambda

A common task with Java streams is to clean up the input data so later steps can work without thinking too hard. Likely the #1 most common cleanup step is to remove nulls from a Collection.

Streams make it easy:

myCollection.stream()
  .filter(Objects::nonNull)
  .do.what.you.need
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Compare with the classic approaches:

while(myCollection.remove(null));
// do what you need, but you better not need that original list, because it's gone...
myCollection.removeAll(Collections.singleton(null));
// do what you need, but you better not need that original list, because it's gone...
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Like the stream approach, these are short and sweet, but unlike the stream approach they modify the original list. The first example is also pretty slow.

I like the stream approach because I can chain additional tasks after the filter task, including map. sorted, reduce and more!. I find the traditional imperative iterative approach to be not only wordier, but conceptually harder to follow.

Latest comments (4)

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pnaranja profile image
Paul

I use streams all the time to filter out results from my collections as well!

I know your title says "Java8", but note that Java 9 has Optional::stream

So now:
.map(this::lookupSettingByName)
.filter(Optional::isPresent)
.map(Optional::get)

Can be transformed to:
.map(this::lookupSettingByName)
.flatMap(Optional::stream)

Here's a reference link - iteratrlearning.com/java9/2016/09/...

Though I understand the filter -> map approach can be more readable

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monknomo profile image
Gunnar Gissel Author

That's a cool thing, for sure!

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roccoprobe profile image
rocco probe

Yup, .filter(Objects::nonNull) is definitely sweet, but one must ask... Why store nulls in a collection in the first place? :)

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monknomo profile image
Gunnar Gissel Author

You have to go to war with the collection you have; or at least, the collections you are given.

Besides, in some contexts, a null at some collection position has a meaning that it lacks in other contexts.

Let's see if I can come up with a concrete example...

In the context of a revolver, I can imagine a collection where nulls are important - you want to know chamber 5 is empty. But in the context of knowing something about the collection bullets in the revolver, we can ignore the nulls.

There are also Swing UI things - JList, JComboBox, etc. where nulls in collections are useful, but I expect the Swing developer is a marginal case these days.

Take a look at this:

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