Why doesn't java.util.Set have get(int index)?

Question

I\'m sure there\'s a good reason, but could someone please explain why the java.util.Set interface lacks get(int Index), or any similar get()

Answer 1

The reason why the Set interface doesn't have a get index-type call or even something even more basic, such as first() or last(), is because it is an ambiguous operation, and therefore a potentially dangerous operation. If a method returns a Set, and you call, say first() method on it, what is the expected result, given that the a generic Set makes no guarantees on the ordering? The resultant object could very well vary between each call of the method, or it might not and lull you into a false sense of security, until the library you're using changes changes the implementation underneath and now you find that all your code breaks for no particular reason.

The suggestions about workarounds listed here are good. If you need indexed access, use a list. Be careful with using iterators or toArray with a generic Set, because a) there is no guarantee on the ordering and b) there is no guarantee that the ordering will not change with subsequent invocations or with different underlying implementations. If you need something in between, a SortedSet or a LinkedHashSet is what you want.

// I do wish the Set interface had a get-random-element though.