Introduction:
In this article, we’ll learn how to remove nulls from a Java List using plain-old Java, Java 8 lambda expression, and some third-party libraries.
So, let’s get started!
Removing nulls from a List In Java:
Let’s explore different ways in which we can remove nulls from a Java List:
1. Java 7 or lower versions:
When working with Java 7 or lower versions, we can use the below construct to remove all nulls from a List:
Java
@Test
public removeAllNullsFromListWithJava7OrLower() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
list.removeAll(Collections.singleton(null));
assertThat(list, hasSize(2));
}
Note that we have created a mutable list here. Attempting to remove nulls from an immutable list will throw java.lang.UnsupportedOperationException.
2. Java 8 or higher versions:
The approach for removing nulls from a Java List for Java 8 or higher versions is pretty intuitive and elegant:
@Test
public removeAllNullsFromListWithJava8() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
list.removeIf(Objects::isNull);
assertThat(list, hasSize(2));
}
We can simply use the removeIf() construct to remove all null values.
If we don’t want to alter the existing list and rather return a new list with all non-null values, we can have:
Java
@Test
public removeAllNullsFromListWithJava8() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
List<String> newList = list.stream().filter(Objects::nonNull)
.collect(Collectors.toList());
assertThat(list, hasSize(4));
assertThat(newList, hasSize(2));
}
We can learn more about Java 8 Stream Collectors here.
3. Apache Commons:
Apache Commons CollectionUtils class provides a filter(Iterable, Predicate) method that can also solve our purpose. The passed-in predicate is applied to all the elements in the list:
Java
@Test
public removeAllNullsFromListWithApacheCommons() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
CollectionUtils.filter(list, PredicateUtils.notNullPredicate());
assertThat(list, hasSize(2));
}
Thereby, filtering out all nulls from the existing list.
4. Google Guava:
The Iterables class in Guava provides removeIf(Iterable, Predicate) method to help us filter our values based on the given predicate. Let’s see how can we use it to our advantage:
Java
@Test
public removeAllNullsFromListUsingGuava() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
Iterables.removeIf(list, Predicates.isNull());
assertThat(list, hasSize(2));
}
Alternatively, if we don’t want to modify the existing list, Guava allows us to create a new filtered list:
Java
@Test
public removeAllNullsFromListUsingGuava() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
List<String> newList = new ArrayList<>(
Iterables.filter(list, Predicates.notNull()));
assertThat(list, hasSize(4));
assertThat(newList, hasSize(2));
}
Java
@Test
public removeAllNullsFromList() {
List<String> list =
new ArrayList<>(Arrays.asList("A", null, "B", null));
List<String> newList = new ArrayList<>(
Iterables.filter(list, Predicates.notNull()));
assertThat(list, hasSize(4));
assertThat(newList, hasSize(2));
}
Conclusion:
In this quick tutorial, we explored multiple ways in which we can remove all nulls from a List in Java.
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Published on Java Code Geeks with permission by Shubhra Srivastava, partner at our JCG program. See the original article here: Java – Remove all nulls from a List Opinions expressed by Java Code Geeks contributors are their own. |
Maybe a better way is to prevent nulls to enter the collection in the first place. As an example of a list disallowing adding nulls as elements you can use PredicatedList from the Apache commons-collection4:
PredicatedList listWithoutNullElements = PredicatedList.predicatedList(new ArrayList(), NotNullPredicate.notNullPredicate());