Why does the compiler state no unique maximal instance exists?

Question

I have the following classes:

public class Obj<T> extends BaseModel {

    public static final String OBJECT = "object";

    public Obj(T object) {
        setObject(object);
    }

    public T getObject() {
        return get(OBJECT);
    }

    public void setObject(T object) {
        set(OBJECT, object);
    }
}

And...

/** This is a 3rd party library class **/
public class BaseModel implements ModelData, Serializable {
  //...members and stuff...

  @SuppressWarnings({"unchecked", "rawtypes"})
  public <X> X get(String property) {
    X obj = null;
    if (start > -1 && end > -1) {
      Object o = map.get(property.substring(0, start));
      String p = property.substring(start + 1, end);
      if (o instanceof Object[]) {
        obj = (X) ((Object[]) o)[Integer.valueOf(p)];
      } else if (o instanceof List) {
        obj = (X) ((List) o).get(Integer.valueOf(p));
      } else if (o instanceof Map) {
        obj = (X) ((Map) o).get(p);
      }
    } else {
      obj = (X) map.get(property);
    }
    return obj;
  }
}

When I compile, I get the following error.

type parameters of <X>X cannot be determined; no unique maximal instance exists for type variable X with upper bounds T,java.lang.Object -> getObject()

It doesn't happen in Eclipse, which, as far as I can tell, is using the same JDK as my Ant build. I've seen the SO thread about the Sun compiler issue, but that seemed to be for static methods declaring types on the fly.

Why am I getting this error, and more importantly, how do I get around it?

So far the only why I've found is to cast in my method like this:

@SuppressWarnings({"unchecked"})
public T getObject() {
    return (T) get(OBJECT); //yuck
}

Telling my I'm on crack and this is the proper way is acceptable.

Answer 1

This is dummy bug that has been fixed in Java SE 7.