Re: [Simple-support] Strange Nullpointer for ElementMap with generics?

[Niall G. <gal...@ya...>]

Hi,

Generics are not reified in Java, this means that the type is erased after compilation. So when you reflectively attempt to acquire the type there is a null pointer exception.

The is no workaround for this, its a limitation of the language unfortunately.

Niall

--- On Sun, 3/29/09, Fabian Kürten <fab...@we...> wrote:

> From: Fabian Kürten <fab...@we...>
> Subject: [Simple-support] Strange Nullpointer for ElementMap with generics?
> To: sim...@li...
> Date: Sunday, March 29, 2009, 5:28 AM
> Hi Group
> 
> I just tried this:
> 
> @Root
> public class MapTest<K, V> {
> 
>     @ElementMap
>     public HashMap<K, V> data;
> 
>     public MapTest() {
>         this.data = new
> HashMap<K, V>();
>     }
> 
>     public static void main(String[] args)
> throws Exception {
>         MapTest<String,
> Integer> mt = new MapTest<String, Integer>();
>         mt.data.put("Eins",
> 1);
>         mt.data.put("Vier",
> 4);
>         mt.data.put("Drei",
> 3);
>         Serializer serializer
> = new Persister();
>         serializer.write(mt,
> System.out);
>     }
> }
> 
> Which failed like:
> Exception in thread "main" java.lang.NullPointerException
>     at
> org.simpleframework.xml.core.Signature.getEntry(Signature.java:102)
>     at 
> org.simpleframework.xml.core.ElementMapLabel.getEntry(ElementMapLabel.java:196)
>     at
> org.simpleframework.xml.core.Signature.getName(Signature.java:196)
>     at 
> org.simpleframework.xml.core.ElementMapLabel.getName(ElementMapLabel.java:214)
>     at
> org.simpleframework.xml.core.CacheLabel.<init>(CacheLabel.java:119)
>     at 
> org.simpleframework.xml.core.LabelFactory.getInstance(LabelFactory.java:67)
>     at
> org.simpleframework.xml.core.Scanner.process(Scanner.java:606)
>     at
> org.simpleframework.xml.core.Scanner.scan(Scanner.java:539)
>     at
> org.simpleframework.xml.core.Scanner.field(Scanner.java:498)
>     at
> org.simpleframework.xml.core.Scanner.scan(Scanner.java:348)
>     at
> org.simpleframework.xml.core.Scanner.<init>(Scanner.java:98)
>     at 
> org.simpleframework.xml.core.ScannerFactory.getInstance(ScannerFactory.java:67)
>     at
> org.simpleframework.xml.core.Support.getScanner(Support.java:161)
>     at
> org.simpleframework.xml.core.Support.getName(Support.java:223)
>     at
> org.simpleframework.xml.core.Source.getName(Source.java:196)
>     at
> org.simpleframework.xml.core.Traverser.getName(Traverser.java:262)
>     at
> org.simpleframework.xml.core.Traverser.write(Traverser.java:185)
>     at
> org.simpleframework.xml.core.Traverser.write(Traverser.java:168)
>     at
> org.simpleframework.xml.core.Persister.write(Persister.java:921)
>     at
> org.simpleframework.xml.core.Persister.write(Persister.java:903)
>     at
> org.simpleframework.xml.core.Persister.write(Persister.java:884)
>     at
> org.simpleframework.xml.core.Persister.write(Persister.java:1000)
>     at
> org.simpleframework.xml.core.Persister.write(Persister.java:982)
>     at
> org.simpleframework.xml.core.Persister.write(Persister.java:963)
>     at MapTest.main(MapTest.java:25)
> 
> I am quite sure the reason are the generics... anyone knows
> more about this?
> 
> Fabian
> 
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