二叉树遍历（前序中序后序，主要是看父节点的输出顺序）

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package tree;public class BinaryTreeDemo {public static void main(String[] args) {//先需要创建一颗二叉树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");//说明，先手动创建该二叉树，后面学习递归方式创建二叉树binaryTree.setRoot(root);root.setLeft(node2);root.setRight(node3);node3.setRight(node4);//测试System.out.println("前序遍历");binaryTree.preOrder();System.out.println("中序遍历");binaryTree.infixOrder();System.out.println("后序遍历");binaryTree.postOrder();}
}class BinaryTree{private HeroNode root;public void setRoot(HeroNode root){this.root = root;}//前序遍历public void preOrder(){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 infixOrder(){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 postOrder(){if (this.root != null){this.root.postOrder();}else {System.out.println("二叉树为空无法遍历");}}
}
class HeroNode{private int no;private String name;private HeroNode left;//默认nullprivate 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;}@Overridepublic String toString() {return "HeroNode{" +"no=" + no +", name='" + name + '\'' +'}';}//编写前序遍历方法public void preOrder(){System.out.println(this);//先输出父节点//递归向左子树前序遍历if (this.left != null){this.left.preOrder();}//递归向右子树前序遍历if (this.right != null){this.right.preOrder();}}//编写中序遍历方法public void infixOrder(){//递归向左子树前序遍历if (this.left != null){this.left.infixOrder();}System.out.println(this);//输出父节点//递归向右子树前序遍历if (this.right != null){this.right.infixOrder();}}//编写后序遍历方法public void postOrder(){if (this.left != null){this.left.postOrder();}if (this.right != null){this.right.postOrder();}System.out.println(this);}
}