gistfile1.java

Multimap<String, String> multimap = Multimaps.newMultimap(
    new TreeMap<String, Collection<String>>(),
    new Supplier<List<String>>() {
      @Override public List<String> get() {
        return new ArrayList<String>(); // could use Lists.newArrayList()
      }
    });

gistfile2.txt

Multimap<String, String> multimap = Multimaps.newMultimap(
    new TreeMap<String, Collection<String>>(), ArrayList<String>#new);