Ansatz:
public class TreeIterator<K> implements Iterator<K>{
// TODO:
public boolean hasNext() { .. }
public K next() { .. }
// ANSATZ: aktuelle Position (Pfad) in Keller
private final Stack<Tree<K>> path = new Stack<Tree<K>>();
public TreeIterator(Tree<K> base) {
this.path.push(base);
} }