Setting List<? extends Interface1>

Question

Trying to do something like:

public interface Order {      
    public List<? extends OrderItem> getItems();  
    public void setItems(List<? extends OrderItem> items);  
}  

public interface OrderItem {  
  // stuff
}  

public calss OrderItemImp implements OrderItem {  
  // stuff
}  

public class OrderImp implements Order {  
    public List<OrderItemImp> getItems() {  
        return items;  
    }  
    public void setItems(List<OrderItemImp> items) {  
        this.items = items;  

    }  
}

Compiler complaining about setItems method. How can I make this work? Thanks.

Answer 1

try replacing

public void setItems(List<? extends OrderItem> items);

with

public <T> void setItems(List<T extends OrderItem> items);

. This is now a generic method

Answer 2

In your Order interface definition, the methods look like a pair of get/set methods i.e. logically a property. In which case they need to have the same type. You need to tie them together via a named type parameter:

public interface Order<T extends OrderItem> {      
    public List<T> getItems();  
    public void setItems(List<T> items);  
}

Not entirely sure if this is the right syntax in Java, but basically both methods must end up referring to the exact same type.