// StringTreeIterateChild.java
// extends the Tree<String> class with an iterator over the children of the 
// owner.
// One would think this could be done generically, but that seems to get the
// compiler hopelessly confused

import java.util.Iterator;

class StringTreeIterateChild  extends Tree<String>
                              implements Iterable<Tree<String>> {

@Override
// Iterates through the children of this.
     public Iterator<Tree<String>> iterator() {
        Iterator<Tree<String>> ic = new Iterator<Tree<String>>() {
           
         private boolean noChildren = (getFirstChild() == null); 
         private Tree<String> c = getFirstChild();  
                            // Keeps track of your place on list
      
@Override
           public boolean hasNext() {
               if (noChildren) return false;
               else return (c != null);
             }

@Override
          public Tree<String> next() { 
              Tree<String> d = c;
              c = c.getNextSibling();
              return d;
             }

@Override
          public void remove() {  // stub
              }
    };
    return ic; 
  }

// Create a tree labelled by strings. Each interior node has 3 children
// level is the depth of the subtree being created.
// If the label on nodes n is w, then the label on the children of n is
// w + "a", w + "b", and w + "c"
//

public static StringTreeIterateChild 
                               ternaryTree(String key, int level) {
   if (level < 0) return null;
   StringTreeIterateChild n = new StringTreeIterateChild();
   n.setLabel(key);
   if (level > 0) {
     n.addChild(ternaryTree(key + "c", level-1));
     n.addChild(ternaryTree(key + "b", level-1));
     n.addChild(ternaryTree(key + "a", level-1));
   }
   return n;
}


public static void main(String[] args) {
  StringTreeIterateChild n = ternaryTree("",3);
  for (Tree<String> c : n) 
      System.out.print(c.getLabel() + " ");
  System.out.println();
  n = (StringTreeIterateChild) n.getFirstChild().getFirstChild();
  for (Tree<String> c : n) 
      System.out.print(c.getLabel() + " ");
  System.out.println();
    
 }
}