import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
class Book {
   int ISBN;

   public Book(int iSBN2) {
       ISBN = iSBN2;
   }

}

class AVLNode

{

   AVLNode left, right;

   Book book;

   int height;

   public AVLNode(Book book)

   {

       left = null;

       right = null;

       this.book = book;

       height = 0;

   }

}

class AVLTree

{

   private AVLNode root;

   public AVLTree()

   {

       root = null;

   }

   public void insert(Book book)

   {

       root = insert(book, root);

   }

   private int height(AVLNode t)

   {

       return t == null ? -1 : t.height;

   }

   private int max(int lhs, int rhs)

   {

       return lhs > rhs ? lhs : rhs;

   }

   private AVLNode insert(Book book, AVLNode top)

   {

       if (top == null)

           top = new AVLNode(book);

       else if (book.ISBN < top.book.ISBN)

       {
           top.left = insert(book, top .left);

           if (height(top .left) - height(top .right) == 2) {

               System.out.print("Imbalance occurred at inserting ISBN " + book.ISBN);

               if (book.ISBN < top.left.book.ISBN) {
                   System.out.println("; fixed in Left Rotation");
                   top = rotateWithLeftChild(top );
               }

               else {
                   System.out.println("; fixed in RightLeft Rotation");
                   top = doubleWithLeftChild(top);
               }

           }

       }

       else if (book.ISBN > top.book.ISBN)

       {

           top.right = insert(book, top.right);

           if (height(top.right) - height(top.left) == 2) {

               System.out.print("Imbalance occurred at inserting ISBN " + book.ISBN);

               if (book.ISBN > top.right.book.ISBN) {
                   System.out.println("; fixed in Right Rotation");
                   top = rotateWithRightChild(top);

               } else {
                   System.out.println("; fixed in LeftRight Rotation");
                   top = doubleWithRightChild(top);
               }

           }

       }


       top.height = max(height(top.left), height(top.right)) + 1;

       return top;

   }

   private AVLNode rotateWithLeftChild(AVLNode k2)

   {

       AVLNode k1 = k2.left;

       k2.left = k1.right;

       k1.right = k2;

       k2.height = max(height(k2.left), height(k2.right)) + 1;

       k1.height = max(height(k1.left), k2.height) + 1;

       return k1;

   }

   private AVLNode rotateWithRightChild(AVLNode k1)

   {

       AVLNode k2 = k1.right;

       k1.right = k2.left;

       k2.left = k1;

       k1.height = max(height(k1.left), height(k1.right)) + 1;

       k2.height = max(height(k2.right), k1.height) + 1;

       return k2;

   }

   private AVLNode doubleWithLeftChild(AVLNode k3)

   {

       k3.left = rotateWithRightChild(k3.left);

       return rotateWithLeftChild(k3);

   }

   private AVLNode doubleWithRightChild(AVLNode k1)

   {

       k1.right = rotateWithLeftChild(k1.right);

       return rotateWithRightChild(k1);

   }

   public void inorder()

   {

       inorder(root);

   }

   private void inorder(AVLNode r)

   {

       if (r != null)

       {

           inorder(r.left);

           System.out.print(r.book.ISBN + " ");

           inorder(r.right);

       }

   }
}

public class AVLTreeTest

{

   public static void main(String[] args) throws FileNotFoundException

   {

       Scanner in = new Scanner(new File("books.txt"));
       AVLTree avlt = new AVLTree();

       while (in.hasNextLine()) {
           Book book = new Book(in.nextInt());
           avlt.insert(book);
       }

       System.out.print("\nIn order : ");
       avlt.inorder();

       in.close();

   }

}

Output

Imbalance occurred at inserting ISBN 564789; fixed in LeftRight Rotation Imbalance occurred at inserting ISBN 321590; fixed i

Books.txt data:

123456
789456
564789
536479
321590
260640
035478
594430
979094
799830
031236
014589
239803
123659