Re: Separate interface and implemenation problem..

From:
Eric Sosman <Eric.Sosman@sun.com>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 04 Jun 2009 10:58:57 -0400
Message-ID:
<1244127523.589052@news1nwk>
MRe wrote:

Hi,

  I had posted this question already to comp.lang.java.help nested
deep in a thread titled "Decouple Javadoc from Java". I am re-posting
here to give it more visibility.

  I am separating interface from implementation (example below) and
have hit on a problem..

  The problem is that I need to access private members of the class
I'm in, but through a different object (and this object is of the
interface type (not the implementation) so it does not have access..
the example is probably better able to explain it.

  I know this is a bit of a hack (for the reason I'm using it, abusing
the type-system to get a feature Java doesn't provide) but I'm sure
someone must have encountered such a problem and found an eloquent
solution?

Thank you for any help,
Kind regards,
Eliott

~~~

////// TreeNode.java //////
public interface TreeNode
{
  public void setParent(TreeNode parentNode);
}

////// TreeNodeImpl.java //////
class TreeNodeImpl implements TreeNode
{
  public void setParent(TreeNode parentNode)
  {
    // problem here: cannot find symbol addChild(TreeNodeImpl)
    parentNode.addChild(this);


     Right. There is no reason to believe that a TreeNode
has an addChild() method; the only methods you can be sure
a TreeNode has are setParent() and the things inherited
from Object. Possible remedies:

     - Include an addChild() method in the TreeNode
       interface definition.

     - Use `((TreeNodeImpl)parentNode).addChild(this)', and
       pray that you're never called with some other kind
       of TreeNode.

  }
  private void addChild(TreeNode childNode) { ... }
}

////// Factory.java //////
public class Factory
{
  public static TreeNode createTreeNode()
  {
    return TreeNodeImpl();


     I guess you mean `new TreeNodeImpl()'.

  }
}


--
Eric.Sosman@sun.com

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