Error Message: Exception in thread "main" java.lang.NullPointerException at Book.addRating(Book.java:25) at Assignment4.main(Assignment4.java:56)

My Code:

DRIVER PROGRAM:

import java.io.; import java.util.; public class Assignment4 { public static void main (String[] args) { // local variables, can be accessed anywhere from the main method char input1 = 'Z'; String inputInfo; String bookTitle; String bookPublisher; double rating; String line = new String(); // instantiate a Book object Book book1 = new Book(); printMenu(); //Create a Scanner object to read user input Scanner scan = new Scanner(System.in); do // will ask for user input { System.out.println("What action would you like to perform?"); line = scan.nextLine(); if (line.length() == 1) { input1 = line.charAt(0); input1 = Character.toUpperCase(input1); // matches one of the case statement switch (input1) { case 'A': //Add Book book1 = new Book(); System.out.print("Please enter the book information:\n"); System.out.print("Enter a book title:\n"); bookTitle = scan.nextLine(); book1.setTitle(bookTitle); System.out.print("Enter its publisher:\n"); bookPublisher = scan.nextLine(); book1.setPublisher(bookPublisher); break; case 'D': //Display Book System.out.print(book1); break; case 'Q': //Quit break; case 'R': //Add Rating System.out.print("Please give a rating of the book:\n"); rating = Double.parseDouble(scan.nextLine()); book1.addRating(rating); break; case '?': //Display Menu printMenu(); break; default: System.out.print("Unknown action\n"); break; } } else { System.out.print("Unknown action\n"); } } while (input1 != 'Q' || line.length() != 1); } /** The method printMenu displays the menu to a user**/ public static void printMenu() { System.out.print("Choice\t\tAction\n" + "------\t\t------\n" + "A\t\tAdd Book\n" + "D\t\tDisplay Book\n" + "Q\t\tQuit\n" + "R\t\tGive Rating\n" + "?\t\tDisplay Help\n\n"); } }

CLASS 1: public class Book { private String title; private String publisher; private Review bookReview; public void book(){ title= "?"; publisher= "?"; } public String getTitle(){ return title; } public String getPublisher(){ return publisher; } public Review getReview(){ return bookReview; } public void setTitle(String aTitle){ title= aTitle; } public void setPublisher(String aPublisher){ publisher= aPublisher; } public void addRating(double rate){ bookReview.updateRating(rate); } public String toString(){ return "\nTitle:\t" + title + ",\n" + "Publisher:\t" + publisher + ",\n" + getReview(); } }

CLASS 2: public class Review { private int numberOfReviews; private double sumOfRatings; private double average; public Review(){ numberOfReviews= 0; sumOfRatings= 0.0; }
public void updateRating(double rating){ numberOfReviews++; sumOfRatings += rating; if(numberOfReviews > 0){ average= sumOfRatings / numberOfReviews; } else{ average= 0.0; } } public String toString(){ if(numberOfReviews > 0) return "Reviews:\t\t" + average + "(" + numberOfReviews + ")"; else return "Reviews:\t0.00(0)"; } }