Re: Encapsulating HashMap bulding

From:

Kevin McMurtrie <mcmurtrie@pixelmemory.us>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 10 May 2010 23:08:23 -0700

Message-ID:

<4be8f458$0$22106$742ec2ed@news.sonic.net>

In article <qf1hu5d02ptja2duic3saa60qgolal9llm@4ax.com>,
Roedy Green <see_website@mindprod.com.invalid> wrote:

Can anyone think of a way to write a method that takes an array of X,
and produces a HashMap<Key,X>

How would you specify the name of the key field/method?

Maybe you could do it by making X implement an interface that defines
the key.

Perhaps you could do it with reflection.

If the key is easily derived from the value, what you might have is a
set rather than a map. If that's not the case, Generics trickery will
make it a simple task.

interface Key
{
  boolean equals(Object other);
  int hashCode ();
  // Other stuff
}

interface Keyed
{
  Key getKey();
}

public <K extends Keyed> HashMap <Key, K> keyedMap (K[] in)
{
  HashMap<Key, K> map= new HashMap<Key, K>(in.length);
  for (K keyed : in)
    map.put(keyed.getKey(), keyed);
  return map;
}

You could even put generics on they Key to support different categories
of keys. It would be nearing the boundary of where Generics stops
making coding easier, though.
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