public class BinaryTree {
 
    private Node root;
     
    /**
     *
     * 内部节点类
     * @author yhh
     */
    private class Node{
        private Node left;
        private Node right;
        private int data;
        public Node(int data){
            this.left = null;
            this.right = null;
            this.data = data;
        }
    }
     
    public BinaryTree(){
        root = null;
    }
     
    /**
     * 递归创建二叉树
     * @param node
     * @param data
     */
    public void buildTree(Node node,int data){
        if(root == null){
            root = new Node(data);
        }else{
            if(data < node.data){
                if(node.left == null){
                    node.left = new Node(data);
                }else{
                    buildTree(node.left,data);
                }
            }else{
                if(node.right == null){
                    node.right = new Node(data);
                }else{
                    buildTree(node.right,data);
                }
            }
        }
    }
     
    /**
     * 前序遍历
     * @param node
     */
    public void preOrder(Node node){
        if(node != null){
            System.out.println(node.data);
            preOrder(node.left);
            preOrder(node.right);
        }
    }
     
    /**
     * 中序遍历
     * @param node
     */
    public void inOrder(Node node){
        if(node != null){
            inOrder(node.left);
            System.out.println(node.data);
            inOrder(node.right);
        }
    }
     
    /**
     * 后序遍历
     * @param node
     */
    public void postOrder(Node node){
        if(node != null){
            postOrder(node.left);
            postOrder(node.right);
            System.out.println(node.data);
        }
    }
     
    public static void main(String[] args) {
        int[] a = {2,4,12,45,21,6,111};
        BinaryTree bTree = new BinaryTree();
        for (int i = 0; i < a.length; i++) {
            bTree.buildTree(bTree.root, a[i]);
        }
        bTree.preOrder(bTree.root);
        bTree.inOrder(bTree.root);
        bTree.postOrder(bTree.root);
    }
 
}