Re: Generics: struggling against type erasure...

z-man <nospam@nowhere.zz>
Fri, 06 Oct 2006 07:55:29 GMT
On 10/06/2006 12:27 AM, Stefan Ram wrote:

z-man <nospam@nowhere.zz> writes:

Let me say: generics type erasure is just a misfeature that's
embarrassingly hiped as a "feature".


sorry for my typo.

  Please be aware that some people in this newsgroup love Java,
  so when you use such wording you might hurt their feelings.

I sincerely didn't want to hurt anybody. Anyway, I think not to be the
only one to complain about such a crippling implementation choice.

  You could have just asked your question without the
  introducing rant.

That was due to my frustration :(

Is there any wizard that can solve this annoying problem (dynamic

  "wizard who can ..."

protected <T,TSuper extends MySuperType<T>> void setEntry(
String key,
T value
TSuper entry = myMap.get(key));
if(entry == null)
 // Owing to that crappy type erasure, neither this works...
 myMap.put(key,entry = new TSuper());
 // ...nor this one (no 'class' member available).
 myMap.put(key,entry = TSuper.class.newInstance());


  This sounds like an FAQ. My own, untested approach in this
  case would be:

public class EntrySetter <T, TSuper extends MySuperType< T >>
{ final Factory<TSuper> factory;

  public EntrySetter( final Factory<TSuper> factory )
  { this.factor = factory; }

  public void setEntry
  ( final java.lang.String key,
    final T value )
  { final TSuper old_entry = myMap.get( key );
    final TSuper entry;
    if( old_entry == null )
    { entry = factory.newInstance();
      myMap.put( key, entry ); }
    else entry = old_entry;
    entry.setValue( value ); }}

I thank you Stefan.
Don't you think, anyway, that being forced by the language to use the
awkward factory pattern is much more a workaround than an elegant solution?

Best Regards

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