Table of Contents
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<Integer> 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<Integer> 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<Integer> 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<Integer> list = Lists.newArrayList(null, 1, null, 2, 3);
List<Integer> 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<Integer> 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<Integer> list = Lists.newArrayList(null, 1, 2, null, 3, null);
List<Integer> listWithoutNulls = list.parallelStream()
.filter(Objects::nonNull)
.collect(Collectors.toList());
}
@Test
public void givenListContainsNulls_whenFilteringSerial_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, 2, null, 3, null);
List<Integer> listWithoutNulls = list.stream()
.filter(Objects::nonNull)
.collect(Collectors.toList());
}
public void givenListContainsNulls_whenRemovingNullsWithRemoveIf_thenCorrect() {
List<Integer> 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.
