Reversible Lists: 3/5/04

NOTE: If you try to run this against your own implementations of List, you'll need to be careful about anyplace where your RecursiveList implementation does a "new" on behalf of the code in Reversible. That is, ReversibleRecursiveList expects that each component List is also a ReversibleRecursiveList -- whereas your RecursiveList implementation most likely calls "new RecursiveList()" at some point -- probably in add. So, what this means is that you've got to worry about ensuring that you "new" an instance of the right kind of list (eg, a ReversibleRecursiveList).

There are two ways to handle this. The first is to define a protected method in RecursiveList that just does a "new RecursiveList()", and then override that method in the subtype. The second way is to define a method inside RecursiveList that creates a new instance of whatever List class it is invoked on. For example:

    protected List newList()
    {
        List l = null;
        try {
            l =  (List)(this.getClass().newInstance());
        } catch (Exception e) {
            System.out.println("I am not a class instance??");
        }
        return l;
    }