1. Introduction
In this short tutorial, we’ll illustrate the difference between Collections.emptyList() and a new list instance.
2. Immutability
The core difference between java.util.Collections.emptyList() and a new list e.g. new ArrayList<>() is immutability.
Collections.emptyList() returns a list (java.util.Collections.EmptyList) that can’t be modified.
When creating a new list instance you can modify it depending on the implementation:
@Test
public void givenArrayList_whenAddingElement_addsNewElement() {
List<String> mutableList = new ArrayList<>();
mutableList.add("test");
assertEquals(mutableList.size(), 1);
assertEquals(mutableList.get(0), "test");
}
@Test(expected = UnsupportedOperationException.class)
public void givenCollectionsEmptyList_whenAdding_throwsException() {
List<String> immutableList = Collections.emptyList();
immutableList.add("test");
}
3. Object Creation
Collection.emptyList() creates a new empty list instance only once, as shown in source code:
public static final List EMPTY_LIST = new EmptyList<>();
public static final <T> List<T> emptyList() {
return (List<T>) EMPTY_LIST;
}
4. Readability
When you want to explicitly create an empty list, then Collections.emptyList() expressed the original intention better e.g. new ArrayList<>().
5. Conclusion
In this to the point article, we’ve focused on the differences between the Collections.emptyList() and a new list instance.
As always full source code is available over on GitHub.
