if ( levelIter.hasChildren() ) {
  levelIter=levelIter.nextLevel(); 
} 
Object nextElt=null;
// if there are more siblings at the current level
if ( levelIter.hasMoreElements() )
  nextElt=levelIter.nextElement();
// the entire level has been processed--go to the parent level
else if (levelIter.hasParent() ) {
  levelIter=levelIter.toParent();
  nextElt=levelIter.nextElement();
} 
return nextElt;

Example 1: Using LevelIterator to implement the tree iterator's next method.