Thread: Generics collections and reflection

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

Can you use public setters for each field? This might better and more easily enforce the generics...create a new instance of the Set/List/Map, then set the value via the setter method (iterate over the Methods rather than Fields). There is also a getGenericType method in the Field class but I haven't yet played with this enough to recommend anything.