用 Java 实现二叉树并且遍历

树是一种在计算机科学中十分重要的数据结构，二叉树作为一种特殊的树，其性质相较于普通的树而言又有很多的不同。

本文提供了一种由 Java 语言实现二叉树并且遍历的方法：

public class BinaryTree {

    private class Node {

        private Node left;
        private Node right;
        private Object value;

        public Node(Object value) {
            this.value = value;
        }

    }

    public Node root = null;

    /*
    *            A
    *       B           C
    *   D      E    F       G
    */

    public void createBinaryTree() {
        root = new Node("A");
        Node B = new Node("B");
        Node C = new Node("C");
        Node D = new Node("D");
        Node E = new Node("E");
        Node F = new Node("F");
        Node G = new Node("G");
        root.left = B;
        root.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        C.right = G;
    }

    public boolean isEmpty() {
        return root == null;
    }

    // 先序遍历
    public void preTraverse(Node node) {
        if (null != node) {
            System.out.println(node.value);
            preTraverse(node.left);
            preTraverse(node.right);
        }
    }

    // 中序遍历
    public void midTraverse(Node node) {
        if (null != node) {
            midTraverse(node.left);
            System.out.println(node.value);
            midTraverse(node.right);
        }
    }

    // 后序遍历
    public void afterTraverse(Node node) {
        if (null != node) {
            afterTraverse(node.left);
            afterTraverse(node.right);
            System.out.println(node.value);
        }
    }

    public static void main(String[] args) {
        BinaryTree b = new BinaryTree();
        b.createBinaryTree();
        b.preTraverse(b.root);
        System.out.println("===========先序遍历=============");
        b.midTraverse(b.root);
        System.out.println("===========中序遍历=============");
        b.afterTraverse(b.root);
        System.out.println("===========后序遍历=============");
    }

}