代码实现

package com.atguigu.tree;
/**
 * 二叉树
 * @author Dxkstart
 * @create 2021-10-17-14:32
 */
public class BinaryTreeDemo {
    public static void main(String[] args) {
        //先需要创建一棵二叉树
        BinaryTree binaryTree = new BinaryTree();
        //创建需要的节点
        HeroNode root = new HeroNode(1, "宋江");
        HeroNode node2 = new HeroNode(2, "吴用");
        HeroNode node3 = new HeroNode(3, "卢俊义");
        HeroNode node4 = new HeroNode(4, "林冲");
        HeroNode node5 = new HeroNode(5, "关胜");
        //说明：
        //我们先手动创建二叉树，后面我们学习递归的方式创建二叉树
        root.setLeft(node2);
        root.setRight(node3);
        node3.setRight(node4);
        node3.setLeft(node5);
        binaryTree.setRoot(root);
        //测试
        System.out.println("前序遍历");//12354
        binaryTree.preOrder1();
        System.out.println("中序遍历");//21534
        binaryTree.infixOrder1();
        System.out.println("后序遍历");//25431
        binaryTree.postOrder1();
    }
}
//定义BinaryTree 二叉树
class BinaryTree{
    private HeroNode root;
    public void setRoot(HeroNode root) {
        this.root = root;
    }
    //前序遍历
    public void preOrder1(){
        if (this.root != null){
            this.root.preOrder();
        }else {
            System.out.println("二叉树为空，无法遍历");
        }
    }
    //中序遍历
    public void infixOrder1(){
        if (this.root != null){
            this.root.infixOrder();
        }else {
            System.out.println("二叉树为空，无法遍历");
        }
    }
    //后序遍历
    public void postOrder1(){
        if (this.root != null){
            this.root.postOrder();
        }else {
            System.out.println("二叉树为空，无法遍历");
        }
    }
}
//先创建HeroNode节点
class HeroNode{
    private int no;
    private String name;
    private HeroNode left;//默认null
    private HeroNode right;//默认null
    public HeroNode(int no, String name) {
        this.no = no;
        this.name = name;
    }
    public int getNo() {
        return no;
    }
    public void setNo(int no) {
        this.no = no;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public HeroNode getLeft() {
        return left;
    }
    public void setLeft(HeroNode left) {
        this.left = left;
    }
    public HeroNode getRight() {
        return right;
    }
    public void setRight(HeroNode right) {
        this.right = right;
    }
    @Override
    public String toString() {
        return "HeroNode{" +
                "no=" + no +
                ", name='" + name + '\'' +
                '}';
    }
    //前序遍历方法
    public void preOrder(){
        System.out.println(this);//先输出父节点
        //递归向左子树遍历
        if (this.left != null){
            this.left.preOrder();
        }
        //递归向右子树遍历
        if (this.right != null){
            this.right.preOrder();
        }
    }
    //中序遍历方法
    public void infixOrder(){
        //递归向左子树中序遍历
        if (this.left != null){
            this.left.infixOrder();
        }
        //输出父节点
        System.out.println(this);
        //递归向右子树中序遍历
        if (this.right != null){
            this.right.infixOrder();
        }
    }
    //后序遍历方法
    public void postOrder(){
        if (this.left != null){
            this.left.postOrder();
        }
        if (this.right != null){
            this.right.postOrder();
        }
        System.out.println(this);
    }
}