二叉树的层次遍历输出

从上到下层次遍历二叉树，并打印输出，使用的是队列，依次存储，输出的时候先把队首输出，同时去除队首元素。
上代码:

package binaryTree;

import java.util.LinkedList;
import java.util.Queue;

/**
 * 二叉树的层次遍历，使用队列
 * 
 * @author duola
 *
 */
public class cengcibianli {

    public static class treeNode {
        int val;
        treeNode leftNode;
        treeNode rightNode;
    }

    public static void cengci(treeNode root) {
        if (root == null)
            return;
        Queue<treeNode> list = new LinkedList<>();
        list.add(root);
        treeNode currNode;
        while (!list.isEmpty()) {
            currNode = list.remove();
            System.out.print(currNode.val + "\t");
            if (currNode.leftNode != null) {
                list.add(currNode.leftNode);
            }
            if (currNode.rightNode != null) {
                list.add(currNode.rightNode);
            }
        }
    }

    public static void main(String[] args) {
        treeNode rootNode = new treeNode();
        treeNode root = new treeNode();
        root.val = 1;
        root.leftNode = new treeNode();
        root.leftNode.val = 2;
        root.leftNode.leftNode = new treeNode();
        root.leftNode.leftNode.val = 3;
        root.leftNode.rightNode = new treeNode();
        root.leftNode.rightNode.val = 4;
        root.rightNode = new treeNode();
        root.rightNode.val = 5;
        root.rightNode.leftNode = new treeNode();
        root.rightNode.leftNode.val = 6;
        root.rightNode.rightNode = new treeNode();
        root.rightNode.rightNode.val = 7;
        cengci(root);
    }

}