java二叉树怎么建立和遍历

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在 Java 中实现二叉树的建立和遍历可以通过定义一个节点类来表示二叉树的节点，然后通过递归的方式来构建二叉树和进行遍历操作。下面是一个示例代码：

// 定义二叉树节点类
class TreeNode {int val;
    TreeNode left;
    TreeNode right;

    public TreeNode(int val) {this.val = val;
        this.left = null;
        this.right = null;
    }
}

// 二叉树类
class BinaryTree {private TreeNode root;

    public BinaryTree() {root = null;
    }

    // 递归插入节点
    private TreeNode insertRecursive(TreeNode current, int val) {if (current == null) {return new TreeNode(val);
        }

        if (val < current.val) {current.left = insertRecursive(current.left, val);
        } else if (val > current.val) {current.right = insertRecursive(current.right, val);
        }

        return current;
    }

    // 插入节点
    public void insert(int val) {root = insertRecursive(root, val);
    }

    // 中序遍历
    private void inorderTraversal(TreeNode node) {if (node != null) {inorderTraversal(node.left);
            System.out.print(node.val + " ");
            inorderTraversal(node.right);
        }
    }

    public void inorder() {inorderTraversal(root);
    }

    // 前序遍历
    private void preorderTraversal(TreeNode node) {if (node != null) {System.out.print(node.val + " ");
            preorderTraversal(node.left);
            preorderTraversal(node.right);
        }
    }

    public void preorder() {preorderTraversal(root);
    }

    // 后序遍历
    private void postorderTraversal(TreeNode node) {if (node != null) {postorderTraversal(node.left);
            postorderTraversal(node.right);
            System.out.print(node.val + " ");
        }
    }

    public void postorder() {postorderTraversal(root);
    }
}

public class Main {public static void main(String[] args) {BinaryTree tree = new BinaryTree();

        tree.insert(5);
        tree.insert(3);
        tree.insert(7);
        tree.insert(2);
        tree.insert(4);
        tree.insert(6);
        tree.insert(8);

        System.out.print("Inorder traversal: ");
        tree.inorder();
        System.out.println();

        System.out.print("Preorder traversal: ");
        tree.preorder();
        System.out.println();

        System.out.print("Postorder traversal: ");
        tree.postorder();
        System.out.println();}
}