如何使用用户输入生成对象？

Question

下面列出的代码不允许创建新书对象，即使有构造函数也不行。我得到了一个NullPointerException，我想这是因为我在初始化对象时出错了。最终目标是创建一个程序，询问用户是否要创建新的图书对象，当用户说“是”时，它会返回并创建另一个图书对象。

public static void main(String args[]) {
        BookstoreBook arrOfBBooks[] = new BookstoreBook[100];
        LibraryBook[] arrOfLBooks = new LibraryBook[200];
        Scanner uinput = new Scanner(System.in);

        int counter = 0;
        do {


            System.out.println("Welcome to the book program!");
            System.out.println("Would you like to create a book object?");
            String creatingAnObjQ = uinput.nextLine();
            creatingAnObjQ = creatingAnObjQ.toUpperCase();
            if (creatingAnObjQ.equals("YES")) {
                System.out.println("Please enter the name of the author, title of the book, and isbn separated by / :");
                String ATI = uinput.nextLine();
                String[] strsOfATI = ATI.split("/");
                System.out.println("Got it!");
                System.out.println("Now, tell me if it is a bookstore book or a library book(enter BB for bookstore book or LB for library book): ");
                String typeOfBook = uinput.nextLine();
                typeOfBook = typeOfBook.toUpperCase();
                //while (!typeOfBook.equals("BB") || !typeOfBook.equals("LB")) {
                //    System.out.println("Invalid entry, try again");
                //   typeOfBook = uinput.nextLine();
                //}
                if (typeOfBook.equals("BB")) {
                    System.out.println("Got it!");
                    //arrOfBBooks[0] = new BookstoreBook("Aj", "Atomic", "123")
                    arrOfBBooks[counter].setAuthor(strsOfATI[0]);
                    arrOfBBooks[counter].setTitle(strsOfATI[1]);
                    arrOfBBooks[counter].setIsbn(strsOfATI[2]);
                    System.out.println("Please enter the price of" + arrOfBBooks[counter].getTitle() + "by" + arrOfBBooks[counter].getAuthor());
                    int priceOfBBook = uinput.nextInt();
                    System.out.println("Is it on sale? (yes/no): ");
                    String ifOnSale = uinput.nextLine();
                    int finalAmountOfSale = 0;
                    int finalPrice = 0;
                    if (ifOnSale.equals("yes")) {
                        System.out.println("Deduction percentage: ");
                        String preAmountOfSale = uinput.nextLine();
                        String[] breakingPercent = preAmountOfSale.split("%");
                        finalAmountOfSale = Integer.parseInt(breakingPercent[0]);
                        finalPrice = (finalAmountOfSale / 100) + priceOfBBook;
                        System.out.println("Got it!");
                    }
                    //arrOfBBooks[counter] book = new BookstoreBook(strsOfATI[0], strsOfATI[1], strsOfATI[2], priceOfBBook, finalPrice);
                    arrOfBBooks[counter].setPrice(priceOfBBook);
                    arrOfBBooks[counter].setFinalPrice(finalPrice);
                    System.out.println("Here is your bookstore ");
                    System.out.println("[" + arrOfBBooks[counter].getIsbn() + "-" + arrOfBBooks[counter].getTitle().toUpperCase() + "by" + arrOfBBooks[counter].getAuthor().toUpperCase() + ", $" + arrOfBBooks[counter].getPrice() + "listed for $" + arrOfBBooks[counter].getFinalPrice());
                }
                //end of BB if loop

            }   //end of saying "Yes" to creating an object


        } while (true);
    }


    class BookstoreBook {

        private String author;
        private String title;
        private String isbn;
        //int percentOff;
        private int price;

        private int finalPrice;


    public BookstoreBook(){

    }
    public BookstoreBook(String author, String title, String isbn){
        this.author = author;
        this.title = title;
        this.isbn = isbn;
    }
    public BookstoreBook(String author, String title, String isbn, int price, int finalPrice) {
        this.author = author;
        this.title = title;
        this.isbn = isbn;
        this.price = price;
        this.finalPrice = finalPrice;
    }

    public BookstoreBook(String author, String title) {
        this.author = author;
        this.title = title;
    }


    //======================================== setters && getters.
    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {

        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }


    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }
    public int getFinalPrice() {
        return finalPrice;
    }

    public void setFinalPrice(int finalPrice) {
        this.finalPrice = finalPrice;
    }
}

Answer 1

改变

arrOfBBooks[counter].setAuthor(strsOfATI[0]);
arrOfBBooks[counter].setTitle(strsOfATI[1]);
arrOfBBooks[counter].setIsbn(strsOfATI[2]);

到

/*
BookstoreBook bb = new BookstoreBook();
bb.setAuthor(strsOfATI[0]);
bb.setTitle(strsOfATI[1]);
bb.setIsbn(strsOfATI[2]);
*/
// useing construct method is more elegant, my bad.
arrOfBBooks[counter] = new BookstoreBook(strsOfATI[0], strsOfATI[1], strsOfATI[2]);

而班级书店的书应该是静态的。

BookstoreBook arrOfBBooks[] = new BookstoreBook[100];

此语句仅创建一个数组对象，但数组的每个插槽仍然为null，因此无法通过调用方法 运算符