Hiding a constructor behind a static creator method?

Question

I\'ve recently discovered an interesting way to create a new instance of an object in Google Guava and Project Lombok: Hide a constructor behind a static creator method. Thi

Answer 1

There are many reasons to use this factory method pattern, but one major reason Guava uses it is that it lets you avoid using type parameters twice when creating a new instance. Compare:

HashBiMap bimap = new HashBiMap();

HashBiMap bimap = HashBiMap.create();

Guava also makes good use of the fact that factory methods can have useful names, unlike constructors. Consider ImmutableList.of, ImmutableList.copyOf, Lists.newArrayListWithExpectedSize, etc.

It also takes advantage of the fact that factory methods don't necessarily have to create a new object. For instance, ImmutableList.copyOf, when given an argument that is itself an ImmutableList, will just return that argument rather than doing any actual copying.

Finally, ImmutableList's factory methods return (non-public) subclasses of ImmutableList such as EmptyImmutableList, SingletonImmutableList and RegularImmutableList depending on the arguments.

None of these things are possible with constructors.