Re: Generics: struggling against type erasure...

From:
ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups:
comp.lang.java.programmer
Date:
5 Oct 2006 22:27:10 GMT
Message-ID:
<factory-20061006002009@ram.dialup.fu-berlin.de>
z-man <nospam@nowhere.zz> writes:

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


  "hyped"

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

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

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());
}

entry.setValue(value);
}


  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 ); }}

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