Re: Sort Map on Value

From:

Eric Sosman <Eric.Sosman@sun.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 25 Aug 2009 17:32:39 -0400

Message-ID:

<1251235959.950461@news1nwk>

Andreas Leitgeb wrote:

Wojtek wrote:

I have a Person object. It contains a pKey (unique) and a name (may
repeat, ie John Smith). The Person object will be held in a collection.
New (or old) people will be added in any order, however I want the
output to be sorted by name. Since the name can repeat I cannot use it
as a key, instead I want to use the pKey.

Normally (sorted on the key) I would use a TreeMap, but I want to use
the key to find a Person, yet sort on the Perons name:

I haven't tried it myself, but isn't the TreeMap designed to be
able to use a custom Ordering? Create a Comparator like Eric did
(for Arrays.sort), but pass it to the TreeMap constructor...

Map persons=new TreeMap<Person>(new Comparator<Person>() {
    public int compare(Person p1, Person p2) {
        return p1.getName().compareTo(p2.getName());
    }
});
persons.put( ... );

TreeMap (any SortedMap) orders on the keys; Wojtek wants an
ordering based on the values the keys map to.

--
Eric.Sosman@sun.com