public void preOrder(BNode root){
        if(root == null) return;
        Stack<BNode> stack = new Stack<BNode>();
        for(BNode iter=root; !stack.empty() || iter!=null; ){
            if(iter == null){
                iter=stack.pop();
            }
            iter.visit();
            if(iter.getRight() != null){
                stack.push(iter.getRight());
            }
            iter=iter.getLeft();
        }
    }

------解决方案--------------------
Java code


package org.zwj.tree;

/**
 * 节点类
 */
class Node
{
    private int data;
    private Node leftChild;
    private Node rightChild;

    public int getData()
    {
        return data;
    }

    public void setData(int data)
    {
        this.data = data;
    }

    public Node getLeftChild()
    {
        return leftChild;
    }

    public void setLeftChild(Node leftChild)
    {
        this.leftChild = leftChild;
    }

    public Node getRightChild()
    {
        return rightChild;
    }

    public void setRightChild(Node rightChild)
    {
        this.rightChild = rightChild;
    }

    public void addNode(Node node)
    {
        if (this.leftChild == null)
        {
            this.leftChild = node;
        } else
        {
            if (this.rightChild == null)
            {
                if (this.leftChild.getData() < node.getData())
                {
                    this.rightChild = node;
                }
            } else
            {
                this.leftChild.addNode(node);
            }
        }
    }

    public void printNode()
    {
        if (this.leftChild != null)
        {
            System.out.print(this.leftChild.getData() + "\t");
            if (this.rightChild != null)
            {
                System.out.print(this.rightChild.getData() + "\t");
            }
            this.leftChild.printNode();
        }
    }
}

/**
 * 一棵树，形状：(节点data<左孩子data<右孩子data)
 * 
 * @author zKF44321
 * 
 */
class Tree
{
    private Node root;

    public Node getRoot()
    {
        return root;
    }

    public void setRoot(Node root)
    {
        this.root = root;
    }

    /**
     * 添加节点
     * 
     * @param data
     */
    public void add(int data)
    {
        Node newNode = new Node();
        newNode.setData(data);

        if (this.root == null)
        {
            this.root = newNode;
        } else
        {
            if (this.root.getData() < newNode.getData())
            {
                this.root.addNode(newNode);
            }
        }
    }

    /**
     * 打印树，从小到大
     */
    public void print()
    {
        if (this.root != null)
        {
            System.out.print(this.root.getData() + "\t");
            this.root.printNode();
        }
    }
}

public class TestTree
{
    public static void main(String args[])
    {
        Tree tree = new Tree();

        tree.add(1);
        tree.add(2);
        tree.add(3);
        tree.add(4);
        tree.add(5);
        tree.add(6);
        tree.add(7);

        tree.print();
    }
}