Question

I have the following in my top class working like a charm:

public class TestA<E extends Test>
{
      List<Vector<E>> list;
      String name, location;

      TestA(String name, String location)
      {
            this.name = name;
            this.location = location;
            list = new ArrayList<Vector<E>>();
      }

      void populate(Test[] arr)
      {
            for(Vector<E> vk : list)
            {
                  // Code here...
            }
      }

}     

class OrderedTest<E extends Test> extends TestA {

      OrderedTest(String name, String location)
      {
            super(name, location);
      }

      void populate(Test[] arr)
      {
            for(Vector<E> vk : list) // ERROR: Cannot convert from element Object to Vector<E>
            {
                  // Code here... 
            }
      }

}

When i try to extend populate() in my subclass i basically want the same method only here i want things ordered so i will pull each Vector in a quicksort method but i dont get any other problems apart from: // ERROR: Cannot convert from element Object to

EDIT: Should i have to implement Iterator for TestA ?

Answer 1

As coded, the two uses of “E” as a generic parameter are independent and disconnected. Vector<E> in one class does not mean the same as Vector<E> in the other.

Change the subclass declaration to:

class OrderedTest<E extends Test> extends TestA<E>

and the E in the superclass declarations is the same E as in OrderedTest.