Passing an immutable list to ImmutableList.copyOf()?

Question

I have the following code:

private static final ImmutableMultimap<String, String> namesToAddress;

public static List<String> getAddresses(String name){
  return ImmutableList.copyOf(namesToAddress.get(name));
}

My question is wheter the defensive copyOf() here is necessary, as the get() returns an immutable list anyway?

Note I am using ImmutableMultiimap from Google Guava.

Thanks.

`ImmutableMultimap#get` returns an `ImmutableCollection`. There's no need to copy it. If you need a `List` however... — Savior, Apr 14 '16 at 17:21
In the Google Guava docs( http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/ImmutableListMultimap.html) it states mmutableMultimap#get returns an ImmutableList... — user1974753, Apr 14 '16 at 17:23
Also, `ImmutableList.copyOf` will not actually copy an `ImmutableList` anyway. — Paul Boddington, Apr 14 '16 at 17:24
@user1974753 You're looking at `ImmutableListMultimap`, but your code has `ImmutableMultimap`. In any case, they're both immutable. — Savior, Apr 14 '16 at 17:29

score 5 · Accepted Answer · answered Apr 14 '16 at 18:15

Couple things (mostly covered in the comments, but as an answer):

If you use ImmutableListMultimap as the type for namesToAddresses, get() will return an ImmutableList; no need to call copyOf or cast or anything
Even if you don't do that, ImmutableMultimap.get() will return an ImmutableCollection; ImmutableCollections have an asList() method to view (or copy if necessary) the collection as an ImmutableList
Calling ImmutableList.copyOf(ImmutableCollection) will end up calling asList() on the collection anyway

Passing an immutable list to ImmutableList.copyOf()?

1 Answers1