Generics collections and reflection

[Franc Crosses]

Hi to all,

I have a simple class, i.e

public class TestRun
{
  private Set<Integer> set;
  private String string;
  public List<String> collection;
  private HashSet<Boolean> hs;
  ...
}

I want to make a factory for this class, so that each collection will be instantiated to a subclass I will define:

public class BusinessObjectFactory
{
  public static Object create(Class<?> c) throws InstantiationException, IllegalAccessException, IllegalArgumentException, ClassNotFoundException
  {
    Object o = (Object) c.newInstance();

    for ( Field field : c.getDeclaredFields() )
    {
      Class<?> fieldClass = field.getType();
      
      Object fieldObject = null;
      
      if(fieldClass.getName().equals("java.util.Set"))
      {
        fieldObject = new HashSet();
      }
      else if(fieldClass.getName().equals("java.util.List"))
      {
        fieldObject = new ArrayList();
      }
      else if(fieldClass.getName().equals("java.util.Map"))
      {
        fieldObject = new HashMap();
      }
      else
      {
        fieldObject = fieldClass.newInstance();
      }
      
      field.setAccessible( true );
      field.set( o, fieldObject);
    }

    return o;
  }

Factory call:

TestRun tr = (TestRun) BusinessObjectFactory.create(TestRun.class);

My question is:

How Have I to instantiate the collection with the right parameter:
new HashSet<Integer>(), new ArrayList<String>(), ...

I tried with fieldObject = new HashSet<?>(); ecc
but it' not possible...

Can someone help me please?

Thanks in advance

Francesco

[David O'Meara]

sorry I haven't tried compiling it, but can you try

public static <T> T create(Class<T> c) //throws etc
  {
    T o =  c.newInstance();

//etc
  }

[David O'Meara]

and now I see I have answered the wrong question. One sec, digging deeper...

[David O'Meara]

I have asked this question before but have not received a answer yet.
If you have ClassA extends GenericClass<ClassB> you can sometimes get the type of ClassB from ClassA using:
((ParameterizedType) fieldClass.getGenericSuperclass()).getActualTypeArguments()[0]

But the same does not work with plain old class of type GenericClass<ClassB>

[Campbell Ritchie]

And welcome to the Ranch

[David O'Meara]

like this

public class TestRun
{
    private Set<Integer> set;
    private String string;
    public List<String> collection;
    private Set<Boolean> hs;
    private Map<Boolean, String> hm;

    public static void main(final String[] args)
    {
        final Class<TestRun> klass = TestRun.class;
        for (final Field field : klass.getDeclaredFields())
        {
            System.out.println(field.getName() + " " + field.getType());
            final Type t = field.getGenericType();
            if (t instanceof ParameterizedType)
            {
                for (final Type inner : ((ParameterizedType) field.getGenericType()).getActualTypeArguments())
                {
                    System.out.println("   " + inner);
                }
            }
        }
    }
}