Trouble with generics

Help.

I'm new to generics and I don't know what did I do wrong in the simplified
example code below. Compiler gives a warning wich is in the comment above
the critical line.

Thanks for the help :-)

// Element.java
public interface Element<T extends Element> {
  public T someMethod(T element);
}

// Box.java
public interface Box<E extends Element> {
  public Box<E> operation(Box<E> box);
  
  public E get(int i, int j);
}

// BigBox.java
public class BigBox<E extends Element> implements Box<E> {
  private final Element[][] data;
  
  public Box<E> operation(Box<E> box){
    // .. some code
    Element[][] result = (Element[][])new Object[2][3];
    // .. some code
    
    // Critical line below!! Compiler warning:
    // Type safety: The method add(Element)
    // belongs to the raw type Element.
    // References to generic type Element<T>
    // should be parametrized
    //
    result[1][1] = data[1][1].someMethod(box.get(1,1));
    
    // .. some code
  }