synchronized,immutable,empty collection

Question

Using Collections class we can make any collection synchronized,immutable or empty

what are there respective uses, when we need to implement these type of collections

Answer 1

After incanting the magick word "google" 3 times, I got this obscure tome which contains the great secrets you are asking for ;-)

http://java.sun.com/docs/books/tutorial/collections/implementations/wrapper.html