[jboss-dev] generic collection item type

[Alexey Loubyansky]

The required information seems to be there.
    // field
    private CollectionClass<Integer, Long, Double> cc;

    public void testMain() throws Exception
    {
       ClassInfo info = (ClassInfo) 
configuration.getTypeInfo(getClass().getDeclaredField("cc").getGenericType()); 


       while(info.isCollection())
       {
          printInfo(info);

          if(info.getGenericInterfaces() != null)
          {
             ClassInfo colInfo = info;
             while (!colInfo.getName().equals(Collection.class.getName()))
             {
                InterfaceInfo[] gi = colInfo.getGenericInterfaces();
                for (InterfaceInfo ii : gi)
                {
                   if (ii.isCollection())
                   {
                      printInfo(ii);
                      colInfo = ii;
                      break;
                   }
                }
             }
          }

          if (info.getGenericSuperclass().isCollection())
          {
             info = info.getGenericSuperclass();
          }
          else
          {
             break;
          }
       }
    }

    private void printInfo(ClassInfo info)
    {
       System.out.println((info.isInterface() ? "interface" : "class") + 
": " + info + ", isCol=" + info.isCollection());
       TypeInfo[] typeArgs = info.getActualTypeArguments();
       if(typeArgs == null)
       {
          System.out.println("no args");
       }
       else
       {
          System.out.println("type args:");
          TypeVariable[] typeVars = info.getType().getTypeParameters();
          for(int i = 0; i < typeArgs.length; ++i)
          {
             System.out.println(" " + typeVars[i].getName() + "=" + 
typeArgs[i].getName());
          }
       }
       System.out.println("---");
    }

    public abstract class CollectionClass<T1 extends Object, T2 extends 
Object, T3 extends Object>
       implements Comparable<T2>, Collection<T1>, java.util.Comparator<T3>
    {
    }

The output is

class: 
ParameterizedClassInfo at 7b7072{org.jboss.xml.binding.test.MainTestCase.org.jboss.xml.binding.test.MainTestCase$CollectionClass<java.lang.Integer, 
java.lang.Long, java.lang.Double>}, isCol=true
type args:
  T1=java.lang.Integer
  T2=java.lang.Long
  T3=java.lang.Double
---
interface: ParameterizedClassInfo at 913750{java.util.Collection<T1>}, 
isCol=true
type args:
  E=java.lang.Object
---

Note, that the interface is printed with the T1 variable. And I can get 
the value of T1 from the super class. But I can't find out using the API 
that T1 is passed to the Collection.

Alexey

Adrian wrote:
> On Mon, 2007-07-30 at 14:39 +0200, Alexey Loubyansky wrote:
>> That's my problem. How can I find out using the API which parameter is 
>> passed to the Collection
>>
>>     public abstract class CollectionClass<T1 extends Object, T2 extends 
>> Object, T3 extends Object>
>>        implements Comparable<T2>, Collection<T1>, java.util.Comparator<T3>
>>     {
>>     }
>>
>> Besides that I have to keep track of arguments from sub- to super 
>> classes. And Collection interface can be extended implemented on 
>> different levels with different type parameters (but those should belong 
>> to the same type hierarchy).
>> But the main problem I think is the first one above.
> 
> That's a very good question. If the class implements
> Collection<Whatever> directly, you can get at this
> information.
> 
> It's just:
> 
> for (ClassInfo intf : myClass.getInterfaces())
> {
>    if (intf.getName().equals(Collection.class.getName())
>      return intf.getActualTypeArguments()[0];
> }
> 
> But if it is on a superclass, there is no way to get
> at this information.
> 
> In the main java reflection api:
> 
> Class.getGenericSuperClass() returns a ParameterizedType
> 
> but from that ParameterizedType there is no route
> to get the generic interfaces.
> 
> e.g.
> public class MyClass extends AbstractCollection<Whatever>
> 
> then there's no way to get at the ParameterizedType
> Collection<Whatever> that AbstractCollection<Whataver> implements.
> 
> What would really be useful would be if there was a
> Class.getAllGenericInterfaces();
> but that doesn't exist.
> 
>