实现二叉排序树， 并分别用先序、中序、后序输出

public class TreeTest {class TreeNode {int val;TreeNode leftNode;TreeNode rightNode;public TreeNode(int val) {this.val = val;leftNode = null;rightNode = null;} }private TreeNode root = null;/*构建一棵二叉排序树*/public void buildTree(int[] array) {for(int i=0; i<array.length; i++) {insertNode(array[i]);}}public void insertNode(int data) {TreeNode newNode = new TreeNode(data);if(root == null) {root = newNode;} else {TreeNode current =  root;TreeNode parent;while(true) {parent = current;if(data < current.val) {current = current.leftNode;if(current == null) {parent.leftNode = newNode;return;}} else {current = current.rightNode;if(current == null) {parent.rightNode = newNode;return;}}}}}/** * 先序遍历 * */public void firstTrace(TreeNode root) {if(root != null) {System.out.print(root.val+" ");firstTrace(root.leftNode);firstTrace(root.rightNode);}}public void firstTrace() {this.firstTrace(this.root);}/** * 中序遍历 * */public void midTrace(TreeNode root) {if(root != null) {midTrace(root.leftNode);System.out.print(root.val+" ");midTrace(root.rightNode);} }public void midTrace() {this.midTrace(root);}/** * 后序遍历 * */public void postTrace(TreeNode root) {if(root != null) {postTrace(root.leftNode);postTrace(root.rightNode);System.out.print(root.val+" ");}}public void postTrace() {this.postTrace(root);}/** * 测试 * */public static void main(String[] args) {TreeTest tt = new TreeTest();int[] array = {2, 8, 7, 4, 9, 3, 1, 6, 7, 5};tt.buildTree(array);tt.firstTrace();System.out.println();tt.midTrace();System.out.println();tt.postTrace();}}