TreeNode implements Iterable<TreeNode<T>>, Serializable, Cloneable { public void traversePostOrder(TraversalAction<TreeNode<T>> action) { if (!action.isCompleted()) { if (!isLeaf()) { for (TreeNode<T> subtree : subtrees()) { subtree.traversePostOrder(action); } } action.perform(this); } } TreeNode(T data);  TreeNode(); abstract Collection<? extends TreeNode<T>> subtrees(); abstract boolean add(TreeNode<T> subtree); abstract boolean dropSubtree(TreeNode<T> subtree); abstract void clear(); abstract TreeNodeIterator iterator(); T data(); void setData(T data); boolean isRoot(); TreeNode<T> root(); TreeNode<T> parent(); boolean isLeaf(); @SuppressWarnings("unchecked") TreeNode<T> find(final T data); Collection<? extends TreeNode<T>> findAll(final T data); boolean hasSubtree(TreeNode<T> subtree); boolean contains(TreeNode<T> node); boolean containsAll(Collection<TreeNode<T>> nodes); boolean remove(TreeNode<T> node); boolean removeAll(Collection<TreeNode<T>> nodes); void traversePreOrder(TraversalAction<TreeNode<T>> action); void traversePostOrder(TraversalAction<TreeNode<T>> action); Collection<TreeNode<T>> preOrdered(); Collection<TreeNode<T>> postOrdered(); Collection<? extends TreeNode<T>> path(TreeNode<T> descendant); TreeNode<T> commonAncestor(TreeNode<T> node); boolean isSiblingOf(TreeNode<T> node); boolean isAncestorOf(TreeNode<T> node); boolean isDescendantOf(TreeNode<T> node); long size(); int height(); int level(); @SuppressWarnings("unchecked") @Override TreeNode<T> clone(); @SuppressWarnings("unchecked") @Override boolean equals(Object obj); @Override int hashCode(); @Override String toString();  }
@Test public void testTraversePostOrder() { String message = "Tree was incorrectly traversed in a post ordered manner"; final Collection<TreeNode<String>> mPostOrderedActual = new ArrayList<>(10); TraversalAction<TreeNode<String>> action = populateCollectionAction(mPostOrderedActual); root.traversePostOrder(action); assertEquals(message, postOrderedExpected(), mPostOrderedActual); }