Question

I’m wondering why class Collections was created. Theoritically methods from this class could be put in class AbstractCollection. So what was the reason seperate utils class was created?

Answer 1

1. Not every collection extends AbstractCollection, and those methods are still applicable there.
2. Having too many methods in the same class makes it harder to understand that class when you’re working your way through the Javadoc.
3. If you’re receiving an Collection from an untrusted caller, being sure that you’re always using the same implementation of e.g. unmodifiableCollection can be helpful.
4. Most of the time, you don’t keep track of the exact implementation type of collections: for example, you write Set<E> set = new HashSet<>(); In this case, you won’t be able to use any methods defined in AbstractCollection that aren’t in Collection.