Iterator - Design Patterns Java - page 256

The next() method checks whether a peek value is loaded and then checks whether it has
reported the interior node of the composite that is being traversed. If not, the next() method
transfers control to next-Descendant() .

The nextDescendant() method exhausts the composite beneath the current child, moving
onto the next child, if necessary:

protected Object nextDescendant()
{
while (true)
{
if (subiterator != null)
{
if (subiterator.hasNext())
{
return subiterator.next();
}
}

if (!children.hasNext())
{
return null;
}
Iterable i = (Iterable) children.next();
if (!visited.contains(i))
{
subiterator = i.iterator(visited);
}
}
}

There is a fair amount of judgment in how you design a composite iterator. A critical decision
in the design just described is that we can expect to be able to add iterator() methods to
the domain classes. You will have to use a different approach if you can't touch the classes
over which you want to iterate. In addition, you may find that you want to introduce other
behaviors to your composite iterators.

Suppose that you decide to add a setShowInterior() method to

the ComponentIterator class. This lets you iterate over just the leaves of a composite:

package com.oozinoz.applications;
import com.oozinoz.util.*;
import com.oozinoz.process.*;
public class ShowLeavesOnly
{
public static void main(String[] args)
{
ProcessComponent pc = ShellProcess.make();
ComponentIterator i = pc.iterator();
i.setShowInterior(false);
while (i.hasNext())
{
System.out.println(i.next());
}
}
}