因为二叉树是单向的，所以要判断当前节点的子节点(左或右)是否是被删除的节点

    //递归删除节点//规定：如果是叶子节点就删除节点，如果非叶子节点就删除子树public void delNode(int no){if (this.left !=null && this.left.no == no){this.left = null;return;}if (this.right != null && this.right.no == no){this.right = null;return;}if (this.left != null){this.left.delNode(no);}if (this.right != null){this.right.delNode(no);}}

    //删除节点public void delNode(int no){if (root != null){//判断root是不是要删除的节点if (root.getNo() == no){root = null;}else {root.delNode(no);}}}

完整代码

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");HeroNode node5 = new HeroNode(5, "关胜");//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);node3.setLeft(node5);//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();//测试查找//前序遍历查找
//        System.out.println("前序遍历查找：~~~~");
//        HeroNode heroNode1 = binaryTree.preOrederSearch(5);
//        if (heroNode1 != null){
//            System.out.println("找到节点：" + heroNode1.toString());
//        }else {
//            System.out.println("没有找到");
//        }
//
        //中序遍历查找
//        System.out.println("中序遍历查找：~~~~");
//        HeroNode heroNode2 = binaryTree.infixOrderSeach(5);
//        if (heroNode2 != null){
//            System.out.println("找到节点：" + heroNode2.toString());
//        }else {
//            System.out.println("没有找到");
//        }
//
//        //后序遍历查找
//        System.out.println("后序遍历查找：~~~~");
//        HeroNode heroNode3 = binaryTree.postOrderSeach(5);
//        if (heroNode3 != null){
//            System.out.println("找到节点：" + heroNode3.toString());
//        }else {
//            System.out.println("没有找到");
//        }//删除前System.out.println("删除前，前序遍历");binaryTree.preOrder();binaryTree.delNode(3);System.out.println("删除后，前序遍历");binaryTree.preOrder();}
}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");}}//前序查找public HeroNode preOrederSearch(int no){if (root != null){return root.preOrderSearch(no);}else {return null;}}//中序查找public HeroNode infixOrderSeach(int no){if (root != null){return root.infixOrderSearch(no);}else {return null;}}//后序查找public HeroNode postOrderSeach(int no){if (root != null){return root.postOrderSearch(no);}else {return null;}}//删除节点public void delNode(int no){if (root != null){//判断root是不是要删除的节点if (root.getNo() == no){root = null;}else {root.delNode(no);}}}}
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);}public static int i = 1, j = 1, k =1;//编写前序查找方法public HeroNode preOrderSearch(int no){System.out.println("前序遍历"+(i++)+"次");if (this.no == no){return this;}HeroNode heroNode = null;if (this.left != null){heroNode = this.left.preOrderSearch(no);}//不等于空说明在左边找到了if (heroNode != null){return heroNode;}if (this.right != null){heroNode = this.right.preOrderSearch(no);}return heroNode;}//中序遍历查找public HeroNode infixOrderSearch(int no){HeroNode heroNode = null;//先判断当前节点的左子节点是否为空，不为空继续进行中序查找if (this.left != null){heroNode = this.left.infixOrderSearch(no);}if (heroNode != null){return heroNode;}System.out.println("中序遍历"+(j++)+"次");if (this.no == no){return this;}if (this.right != null){heroNode = this.right.infixOrderSearch(no);}return heroNode;}//后序遍历查找public HeroNode postOrderSearch(int no){HeroNode heroNode = null;//判断当前节点的左子节点是否为空，不为空，则递归后序遍历查找if (this.left != null){heroNode = this.left.postOrderSearch(no);}if (heroNode != null){return heroNode;}//判断当前节点的右子节点是否为空，不为空，则递归后序遍历查找if (this.right != null){heroNode = this.right.postOrderSearch(no);}if (heroNode != null){return heroNode;}System.out.println("后序遍历"+(k++)+"次");//左右子树都没有找到，比较当前节点是不是if (this.no == no){return this;}return heroNode;}//递归删除节点//规定：如果是叶子节点就删除节点，如果非叶子节点就删除子树public void delNode(int no){if (this.left !=null && this.left.no == no){this.left = null;return;}if (this.right != null && this.right.no == no){this.right = null;return;}if (this.left != null){this.left.delNode(no);}if (this.right != null){this.right.delNode(no);}}
}