Re: Searching easiest way to convert/copy a (Hash)Set<--->List

Lew <>
Wed, 12 Jan 2011 09:27:30 -0800 (PST)
On Jan 12, 9:39 am, Eric Sosman <esos...@ieee-dot-org.invalid> wrote:

On 1/12/2011 9:34 AM, Eric Sosman wrote:

On 1/12/2011 9:19 AM, Gianni Galore wrote:

Assume I have two variables:

List mylist = new List();

This won't compile, but "we know what you meant."

Set myhashset = new HashSet();

Assume I got a filled List. How can I convert/copy most easily the
content into a HashSet resp. vice versa?

myhashset.addAll(mylist) seems easy enough.

     Missed the "vice versa:" mylist.addAll(myhashset). Note tha=


the original List's order will not necessarily be preserved: If you
start with a List of (A,B,C), put those into a Set {A,B,C}, and
extract to a List again you might get (C,A,B). That's because a
Set has no notion of "order," just of "membership."

     Also, if the original List is (A,B,C,A), the Set (and the fina=


List) will have only three elements.

There's a wonderful help called the API Javadocs:
the briefest perusal of which shows

the briefest perusal of which shows
(not surprising, given that the method is required by

There are also constructors in the implementing classes you might
to name two.

It's REALLY a good idea to study the collections types, and REALLY
even a better one to be in the habit of reading the Javadocs. You
won't be a good Java programmer until you do.

(Also, please stop cross-posting your questions.)


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