Re: Best way to check if all elements in a List are unique

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 1 Mar 2010 21:06:55 -0800

Message-ID:

<hmi6dh$cjm$1@news.eternal-september.org>

John B. Matthews wrote:

In article <hmhim4$n8d$1@news.eternal-september.org>,
"Mike Schilling" <mscottschilling@hotmail.com> wrote:

John B. Matthews wrote:

In article
<95bd0b1b-e372-4981-a6cf-eed5a58e4461@u19g2000prh.googlegroups.com>,
laredotornado <laredotornado@zipmail.com> wrote:

I'm using Java 1.5. Given a java.util.List that I know to have at
least one element, what is the best way to check that all elements
in the list are unique ?

You should be able to construct a Set, say TreeSet, of the List
elements and see if the sizes match.

TreeSet requires the elements be comparable. HashSet will work for
any element type.

Good points; but if the elements are Comparable (or admit a
Comparator), TreeMap won't require re-hashing.

But the HashSet shouldn't require expansion, since it knows the maximum
number of elements it will hold, while the TreeSet may require rebalancing.
And rehashing is more or less free if the objects precompute their hash
(like Strings) or use the default "identity" hash. I'd like to see numbers
before concluding that TreeMap is cheaper.