Re: [Switch()]From String to enum

Lew <>
Tue, 15 Jan 2008 19:39:42 -0500
Daniel Moyne wrote:

To extend this topic a little bit : in Java is there any simple built-in
method to get the whole collection of instances already created of a
class ; here the whole collection of instances can easily be accessed with
values() ; then iteration is made possible to search for a particular
instance fulfilling some conditions (here the unique member = a particular
value) ?

Only for enums.

You can, of course, create your own Collection (Set, List, Map) of instances
of any non-enum class. There is a more-or-less standard idiom for that,
called a "registry".

public class RegisteredInstance
  private static final Map <String, RegisteredInstance> registry =
    new ConcurrentHashMap <String, RegisteredInstance> ();

  private final String name;

  public RegisteredInstance( String n )
    if ( n == null )
      throw new IllegalArgumentException( new NullPointerException(
        "name is null" ));
    name = n;
    registry.put( name, this );

// add @Overrides for equals(), hashCode()
// add other logic, including registry access

If you don't need associative lookup of the instances, you could use a Set or
a List for the registry instead, and iterate at need.

That is not the right way to use a semicolon in English.

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