List E .add always returns true (or throws)?

Question

http://download.java.net/jdk6/docs/api/java/util/List.html#add(E)
"Returns:
true (as specified by Collection.add(E))"
but http://download.java.net/jdk6/docs/api/java/util/Collection.html#add(E)
"Returns:
true if this collection changed as a result of the call"
and also says, "(Returns false if this collection does not permit duplicates and already contains the specified element.)"
I am implementing a list that doesn't allow duplicate elements -- which the List<E> doc says "is not inconceivable ... but we expect this usage to be rare." My rarity notwithstanding, I don't understand the parenthetical remark in the Returns doc for List, and I don't know whether to return false or throw if an attempt is made to add a duplicate to my list.

Answer 1

Err... stupid me! I totally forgot about LinkedHashSet which looks like it will solve your problem directly, with no code!
Meanwhile, a question arose on my reading of the
javadoc on LinkedHashMap. It says, "It can be used
to produce a copy of a set that has the same order as
the original, regardless of the original set's
implementation:void foo(Set m) {
Set copy = new LinkedHashSet(m);
}I don't understand how the LinkedHashSet copy
constructor can produce a copy that "has the same
order" unless the implementation of the original set
-- in particular, I guess, its iterator -- guarantees
some ordering. But then that would contradict
"regardless of the original set's implementation."Looking at the implementation, I would suggest that the JavaDoc is poorly worded. What it means is that this copy constructor will copy everything out of the first set into the new set and the order of the new set will be consistent with the order of the elements returned by the first set's iterator. (Which, of course, is likely to be undefined for the majority of Set implementations.)