结点类:

package DataStrcture.avltreedemo;

public class AVLTreeNode {
    public AVLTreeNode leftNode;
    public AVLTreeNode rightNode;
    public int value;

    //左旋转和右旋转
    public void leftRotation() {
        AVLTreeNode newNode = new AVLTreeNode(this.value);
        newNode.leftNode = this.leftNode;
        newNode.rightNode = this.rightNode.leftNode;
        this.value = this.rightNode.value;
        this.rightNode = this.rightNode.rightNode;
        this.leftNode = newNode;
    }

    public void rightRotation() {
        AVLTreeNode newNode = new AVLTreeNode(this.value);
        newNode.leftNode = this.leftNode.rightNode;
        newNode.rightNode = this.rightNode;
        this.value = this.leftNode.value;
        this.leftNode = this.leftNode.leftNode;
        this.rightNode = newNode;
    }

    //得到二叉树的高度, 左子树的高度, 右子树的高度
    public int height() {
        return Math.max(leftNode == null ? 0 : leftNode.height(),
                rightNode == null ? 0 : rightNode.height()) + 1;
    }

    public int leftHeight() {
        if (this.leftNode != null)
            return this.leftNode.height();
        return 0;
    }

    public int rightHeight() {
        if (this.rightNode != null)
            return this.rightNode.height();
        return 0;
    }

    //二叉树的创建(添加结点, 构建关系)
    public void addNode(AVLTreeNode node) {
        //左子树
        if (node.value <= this.value) {
            if (this.leftNode == null) {
                this.leftNode = node;
            } else {
                this.leftNode.addNode(node);
            }
            //右子树
        } else {
            if (this.rightNode == null) {
                this.rightNode = node;
            } else {
                this.rightNode.addNode(node);
            }
        }
    }

    //中序遍历
    public void midOrder() {
        if (this.leftNode != null) this.leftNode.midOrder();

        System.out.println(this);

        if (this.rightNode != null) this.rightNode.midOrder();
    }

    //构造器, toString
    public AVLTreeNode(int val) {
        this.value = val;
    }

    public String toString() {
        return "Node{ value=" + value + "}";
    }
}

平衡二叉树类:

package DataStrcture.avltreedemo;

public class AVLTreeDemo {
    //初始化根节点
    private AVLTreeNode root;

    public AVLTreeDemo(AVLTreeNode node) {
        this.root = node;
    }

    //测试方法
    public static void main(String[] args) {
        int arr[] = {10,9,11,6,5,7,8};
        AVLTreeDemo tree = new AVLTreeDemo(null);
        for (int x : arr) {
            tree.add(new AVLTreeNode(x));
        }
        tree.midOrder();
        System.out.println("平衡二叉树左子树的高度为: "+tree.root.leftHeight());
        System.out.println("平衡二叉树右子树的高度为: "+tree.root.rightHeight());

    }

    //遍历二叉树
    public void midOrder() {
        if (root == null) {
            System.out.println("二叉树为空, 遍历失败");
        } else {
            root.midOrder();
        }
    }

    //添加结点到二叉树
    public void add(AVLTreeNode node) {
        if (root == null) {
            root = node;
        } else {
            root.addNode(node);
            //左旋转
            if (root.leftHeight() - root.rightHeight() > 1) {
                if (root.leftNode.rightHeight() - root.leftNode.leftHeight() > 0) {
                    root.leftNode.leftRotation();
                }
                //右旋转
                root.rightRotation();
                return;
            }
            if (root.rightHeight() - root.leftHeight() > 1) {
                    if (root.rightNode.leftHeight() - root.rightNode.rightHeight() > 0) {
                        root.rightNode.rightRotation();
                    }
                    root.leftRotation();

                return;
            }
        }
    }
}