Question

In Java 5, If i have a Set, and i add two objects to the Set. When I retrieve the objects, will it give me back in the same order as I added?
I am not able to find the answer to this. Does it depend on which Set implementation I use?

Answer 1

Yes, it depends on which implementation you use. For example, LinkedHashSet will preserve insertion order:

Hash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order). Note that insertion order is not affected if an element is re-inserted into the set. (An element e is reinserted into a set s if s.add(e) is invoked when s.contains(e) would return true immediately prior to the invocation.)

… but HashSet won’t:

It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.