Sort Map on Value

From:
Wojtek <nowhere@a.com>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 25 Aug 2009 13:12:01 -0700
Message-ID:
<mn.cb187d98776803be.70216@a.com>
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:

TreeMap<String,Person> people = new TreeMap<String,Person>();
....

Person addPerson(String pKey, String name)
{
  Person person = people.get(pKey);

  if ( person == null )
  {
     person = new Person(pKey,name);
     people.put(pKey,person);
  }

  return person;
}

I thought of creating my own Comparitor, however the TreeMap insists
that the comparitor needs to sort on the String (pKey) rather than the
value (Person).

I know I can:
- use two collections, one which is used for lookup the other for
sorting
- ignore the TreeMap and use a simple Map, then array sort the
values().toArray(). (Thanks Roedy)
- make a key which is the (name + pKey) but this would create large
keys.

I was hoping there was a more elegant way.

Yes, a Google search turned this up with solutions, however most of
those did not use Generics :-(

--
Wojtek :-)

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