Lists.newArrayList vs new ArrayList

What is the best construction for creating a List of Strings? Is it Lists.newArrayList() (from guava) or new ArrayList()?

is it just a personal preference?
or is it just Type generic type inference?
or is there any theoretical or practical value in using Lists.newArrayList()?

8 Answers

The guava builder saves typing the type arguments multiple times. Compare:

List<Foo<Bar, Baz>> list = Lists.newArrayList(); List<Foo<Bar, Baz>> list = new ArrayList<Foo<Bar, Baz>>(); 

In Java 7 it's a bit obsolete though, because you have the diamond operator:

List<Foo<Bar, Baz>> list = new ArrayList<>(); 

From Guava's source:

public static <E> ArrayList<E> newArrayList() { return new ArrayList<E>(); } 

All that's doing is allowing for type inference - no difference at runtime.

Add one point, overloading version of Lists.newArrayList() is more useful:

• Lists.newArrayList(E... elements)
• Lists.newArrayList(Iterable<? extends E> elements)
• Lists.newArrayList(Iterator<? extends E> elements)

provide more useful functions than new ArrayList().

For example: new ArrayList() cannot do:

Lists.newArrayList("a","b"); Lists.newArrayList(anIterable); 

This is what Lists.newArrayList does:

@GwtCompatible(serializable = true) public static <E> ArrayList<E> newArrayList() { return new ArrayList<E>(); } 

So these two are basically the same, with using newArrayList having the advantage on not having to duplicate the generic type. This is very helpful on complex generics:

List<Map<X,List<Y>> list = new ArrayList<Map<X,List<Y>>(); List<Map<X,List<Y>> list = Lists.newArrayList(); 

As explained here, the main motivations for using Lists, Sets etc are to improve the readability/duplication in your code, and for the type inference.

Java 8 approach for overloaded constructors.

If you would like to use the overloaded constructors from Guava, I would recommend another way using Java 8 Stream Builder.

List<String> listTest = Stream.<String>builder .add("Hello").add("My Name").add("Blah") .build().collect(Collectors.toList()); 

If you are on a Java version 9+, you can use below. But this method returns an ImmutableList so you can't add more elements to it.

List.of("My","Name", "IS", "this"); 

As noted, Java 7 makes this obsolete, but I use the factory method because it makes changing the type of a list, set, map or whatever easier later.

You can use Arrays.asList() from java.util so you don't have to use Guava:

List<String> list = Arrays.asList("one","another", null, "one_more") 

(btw, Stream Builder from Java 8, is also an option, but it's too verbose and overkill for most common use cases)