Here is an (untested) implementation of a ReverseIterable. When iterator() is called it creates and returns a private ReverseIterator implementation, which simply maps calls to hasNext() to hasPrevious() and calls to next() are mapped to previous(). It means you could iterate over an ArrayList in reverse as follows:
ArrayList<String> l = ...
for (String s : new ReverseIterable(l)) {
System.err.println(s);
}
Class Definition
public class ReverseIterable<T> implements Iterable<T> {
private static class ReverseIterator<T> implements Iterator {
private final ListIterator<T> it;
public boolean hasNext() {
return it.hasPrevious();
}
public T next() {
return it.previous();
}
public void remove() {
it.remove();
}
}
private final ArrayList<T> l;
public ReverseIterable(ArrayList<T> l) {
this.l = l;
}
public Iterator<T> iterator() {
return new ReverseIterator(l.listIterator(l.size()));
}
}