Java 二叉树广度优先遍历

private void levelOrderTraversalNoRecursive()
{
if (root==null) {
System.out.println("empty tree");
}
ArrayDeque<TreeNode> queue = new ArrayDeque<TreeNode>();
queue.add(root);

while(!queue.isEmpty())
{
TreeNode ctn = queue.remove();
System.out.print(ctn.value+"  ");

if (ctn.left!=null) {
queue.add(ctn.left);
}
if (ctn.right!=null) {
queue.add(ctn.right);
}
}
}