Question

I am working with tree’s in java and I have the following interface for a simple unordered tree with a self reference:

public interface Node<N extends Node> {

  public N getParent();
  public void setParent(N parent);

  public Collection<N> getChildren();

  public void addChild(N node);
  public void removeChild(N node);

  public N getRootNode();

  ... more ...
}

The idea of course is to create a typesafe Node

  public abstract class ParentChildNode<E extends Node> implements Node<E> {

problem that really annoys me is the warning i get:

ParentChild is a raw type. References to generic type Node<N> should be parameterized

warning on this line:

public interface Node<N extends Node> {

warning on this line:

    public abstract class ParentChildNode<E extends ParentChild> implements ParentChild<E>  

I can do:

public interface Node<N extends Node<?>> {

but i fear im treading into yuckness territory. i can suppress the warning but thats not allowed where i work.

any suggestions? I noticed java.util collections API does not have any warnings anywhere.

thanks in advance

Answer 1

how about something like this (paralleling the declaration of the Enum class):

public interface Node<N extends Node<N>> {

  public N getParent();
  public void setParent(N parent);

  public Collection<N> getChildren();

  public void addChild(N node);
  public void removeChild(N node);

  public N getRootNode();

  ... more ...
}

public abstract class ParentChildNode implements Node<ParentChildNode> {