ArrayList null

This quick tutorial is going to show how to remove all null elements from a List, using plain Java, Guava, the Apache Commons Collections and the newer Java 8 lambda support.

This article is part of the Java Back to Basic series here on Baeldung.

1. Remove Nulls From a List Using Plain Java

The Java Collections Framework offers a simple solution for removing all null elements in the List a basic while loop:

@Test public void givenListContainsNulls_whenRemovingNullsWithPlainJava_thenCorrect[] { List list = Lists.newArrayList[null, 1, null]; while [list.remove[null]]; assertThat[list, hasSize[1]]; }

Alternatively, we can also use the following simple approach:

@Test public void givenListContainsNulls_whenRemovingNullsWithPlainJavaAlternative_thenCorrect[] { List list = Lists.newArrayList[null, 1, null]; list.removeAll[Collections.singleton[null]]; assertThat[list, hasSize[1]]; }

Note that both these solutions will modify the source list.

2. Remove Nulls From a List Using Google Guava

We can also remove nulls using Guava and a more functional approach, via predicates:

@Test public void givenListContainsNulls_whenRemovingNullsWithGuavaV1_thenCorrect[] { List list = Lists.newArrayList[null, 1, null]; Iterables.removeIf[list, Predicates.isNull[]]; assertThat[list, hasSize[1]]; }

Alternatively, if we don't want to modify the source list, Guava will allow us to create a new, filter list:

@Test public void givenListContainsNulls_whenRemovingNullsWithGuavaV2_thenCorrect[] { List list = Lists.newArrayList[null, 1, null, 2, 3]; List listWithoutNulls = Lists.newArrayList[ Iterables.filter[list, Predicates.notNull[]]]; assertThat[listWithoutNulls, hasSize[3]]; }

3. Remove Nulls From a List Using Apache Commons Collections

Let's now look at a simple solution using the Apache Commons Collections library using a similar functional style:

@Test public void givenListContainsNulls_whenRemovingNullsWithCommonsCollections_thenCorrect[] { List list = Lists.newArrayList[null, 1, 2, null, 3, null]; CollectionUtils.filter[list, PredicateUtils.notNullPredicate[]]; assertThat[list, hasSize[3]]; }

Note that this solution will also modify the original list.

4. Remove Nulls From a List Using Lambdas [Java 8]

Finally let's look at a Java 8 solution using Lambdas to filter the List; the filtering process can be done in parallel or serial:

@Test public void givenListContainsNulls_whenFilteringParallel_thenCorrect[] { List list = Lists.newArrayList[null, 1, 2, null, 3, null]; List listWithoutNulls = list.parallelStream[] .filter[Objects::nonNull] .collect[Collectors.toList[]]; } @Test public void givenListContainsNulls_whenFilteringSerial_thenCorrect[] { List list = Lists.newArrayList[null, 1, 2, null, 3, null]; List listWithoutNulls = list.stream[] .filter[Objects::nonNull] .collect[Collectors.toList[]]; } public void givenListContainsNulls_whenRemovingNullsWithRemoveIf_thenCorrect[] { List listWithoutNulls = Lists.newArrayList[null, 1, 2, null, 3, null]; listWithoutNulls.removeIf[Objects::isNull]; assertThat[listWithoutNulls, hasSize[3]]; }

And that's it some quick and very useful solutions for getting rid of all null elements from a List.

5. Conclusion

In this article, we were able to explore the different approaches we can have to remove nulls from a List using Java, Guava or Lambdas.

The implementation of all of these examples and snippets can be found in the GitHub project. This is a Maven-based project so it should be easy to import and run.

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