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From Alex Blewitt <>
Subject Re: [General] Container interface and AbstractContainer
Date Thu, 14 Aug 2003 12:27:34 GMT
> But then Adrian Jackson wrote:
>> From: Alex Blewitt 
>> []
>>> Can you use ListIterator to go from the end?
>> You can work from the end if you *start* at the end (by passing an
>> appropriate argument to the listIterator() method of your list) but 
>> once
>> you've got the iterator you're limited to working backwards and
>> forwards. If we want complete flexibility of how to navigate the
>> collection of components, then returning a List rather than a
>> ListIterator might be the only option.
> So how about this then:
>   public interface Container extends Component {
>     public List getComponents();
>     public void addComponent(Component component);
>     public void removeComponent(Component component);
>   }

I think it's a good idea to return a LIst; that way, you can go through 
it forwards or backwards.

One danger with returning a mutable list is that the Collections class 
has a method:
pubic class Collections {
public void reverse(List list);

What that does is it reverses the list itself, rather than returning a 
new copy that is reversed. So if someone did:


then they'd actually end up reversing the order of the container's 
components, which is Not A Good Thing

> But then we have the question - should the List be immutable or not?
> I think it should be a write through list, as this is a core class and
> should be as flexible as possibe.  So it is worth the effort to support
> the full Collection API.

Plus, if it's mutable, then you can do:

container.getComponents().add(new Applet())

which again isn't desirable.

What I propose is that you return a read-only wrapper of the class 
(which only needs instantiating once), and then if at a later stage we 
find we need write-through functionality we can look at (a) why, and 
(b) if there's a better way of doing it.

public interface Container extends Component {
private List mutable = new LinkedList();
private List immutable = Collections.unmodifiabeList(mutable);
public List getComponents {
   return immutable;
public void addComponent(Component c) {

> However, while this is working towards a good abstract Collection,
> I would still like to hear from Dain or Jeremy what they intended
> the plugin methods to be for and where they should go?

I'd also question; is 'addComponent(Component c)' more 
readable/descriptive than 'add(Component c)'? We know it's a container, 
which is designed to manage components, so hopefully it's obvious that 
it's components you're adding ...


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