前序遍历二叉树

class TreeNode {    int val;    TreeNode left;    TreeNode right;    TreeNode(int x) {        val = x;    }}public class traversal {    public static void main(String[] args) {        TreeNode t = CreateTree();        dfs(t);    }    //深度优先遍历    public static void dfs(TreeNode root) {        if (root == null) {            return;        }        System.out.println(root.val);        dfs(root.left);        dfs(root.right);    }    public static TreeNode CreateTree() {        TreeNode t1 = new TreeNode(1);        TreeNode t2 = new TreeNode(2);        TreeNode t3 = new TreeNode(3);        TreeNode t4 = new TreeNode(4);        TreeNode t5 = new TreeNode(5);        TreeNode t6 = new TreeNode(6);        TreeNode t7 = new TreeNode(7);        TreeNode t8 = new TreeNode(8);        TreeNode t9 = new TreeNode(9);        TreeNode t10 = new TreeNode(10);        t1.left = t2;        t1.right = t3;        t2.left = t4;        t2.right = t5;        t4.left = t7;        t4.right = t8;        t8.right = t10;        t3.left = t6;        t6.left = t9;        return t1;    }}