Todd O'Bryan wrote:
>public interface TreeNode {
> TreeNode getParent();
> List getChildren();
> Object getValue();
>}
>public class TypeATreeNode implements TreeNode {
> public TypeATreeNode getParent() {
> // code
> }
Your implementation of getParent() is returning a narrower type than the
interface's getParent(). So either you're not implementing a required
method, or the return-types are incompatible. I.e. not every TreeNode is a
TypeATreeNode.
Declare the implementations to return TreeNode.
>If so, why not?
Because the return-types won't match.
Read the sections in the Java Language Specification about return-types,
and also see the sections on implicit widening and non-implicit narrowing.
-- GG
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