如何在Java数组中按字母顺序对自定义对象进行排序？

我如何inventory按字母顺序对数组进行排序？

这是我正在从事的项目。我尝试使用，Arrays.sort(inventory);但是没有用。

有人可以告诉我我做错了吗？

书本类：

//Filename: BookStore.java
//Description: Purpose is to display what books are in stock and ISBN, title, author name, year, publishers name, and price.
//Author Name: David Finocchi
//Date: 01/19/2014
import java.util.Arrays;
import java.text.DecimalFormat;

class Book {
    protected long isbn;
    protected String title;
    protected String autName;
    protected int year;
    protected String pubName;
    protected double price;
    protected int quantity;


    // Constructor
    public Book(long isbn, String title, String autName, int year, String pubName, double price) {
        setIsbn(isbn);
        setTitle(title);
        setAut(autName);
        setYear(year);
        setPub(pubName);
        setPrice(price);
    }

    // methods for class variables
    public long getIsbn() {
        return isbn;
    }

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

    public String getTitle() {
        return title;
    }

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

    public String getAut() {
        return autName;
    }

    public void setAut(String autName) {
        this.autName = autName;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public String getPub() {
        return pubName;
    }

    public void setPub(String pubName) {
        this.pubName = pubName;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getQuantity() {
        return quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }

    public double calTotal() {
        return price;
    }

    //toString for the book array
    public String toString() {
        return "ISBM: " + isbn + "\n" + "Title: " + title + "\n" + "Author's Name: " + autName + "\n" + "Year Published: " + year + "\n" + "Publisher's Name: " + pubName + "\n" + "Price: $" + price + "\n\n";
    }

}// end class Book

电子书类：

class EBook extends Book {

    private String website;

    //constructor and super
    public EBook(long isbn, String title, String autName, int year,
                 String pubName, double price, String website) {
        super(isbn, title, autName, year, pubName, price);
        setWebsite(website);
    }

    // get and set
    public String getWebsite() {
        return website;
    }


    public void setWebsite(String website) {
        this.website = website;
    }

    public double discount() {
        return price * 0.10;
    }

    DecimalFormat money = new DecimalFormat("$0.00");

    //toString for the Book array
    public String toString() {
        return "ISBM: " + isbn + "\n" + "Title: " + title + "\n" + "Author's Name: " + autName + "\n" + "Year Published: " + year + "\n" + "Publisher's Name: " + pubName + "\n" + "Price: " + money.format(price) + "\n" + "Website: " + website + "\n" + "Discount: " + money.format(discount()) + "\n\n";
    }

}//end class EBook

BookStore类（使用main方法）：

public class BookStore {
    //main method
    public static void main(String[] args) {
        // book array
        Book[] inventory = new Book[5];

        EBook a = new EBook(75260012L, "David goes to School", "David Shannon", 2010, "Shannon Rock", 11.98, "http://www.tinyurl.qqwert67o9");
        Book b = new Book(7423540089L, "No David!", "David Shannon", 2009, "Shannon Rock", 12.99);
        Book c = new Book(743200616L, "Simple Abundance", "Sarah Breathnach", 2009, "Scribner", 14.99);
        EBook d = new EBook(78137521819L, "The very hungry caterpillar", "Eric Carle", 2005, "Philomel Books", 13.99, "http://www.tinyurl.fguopt8u90");
        Book e = new Book(9781416987116L, "We're going on a bear hunt", "Michael Rosen", 2009, "McElderry", 15.99);

        inventory[0] = a;
        inventory[1] = b;
        inventory[2] = c;
        inventory[3] = d;
        inventory[4] = e;

        double total = 0.0;

        //print text to user
        System.out.println("Bookstore Items:" + "\n");
        //print array
        for (int i = 0; i < inventory.length; i++) {
            System.out.println(inventory[i]);
            total += inventory[i].getPrice();
        }
        //print total
        DecimalFormat money = new DecimalFormat("$0.00");
        System.out.printf("Total Inventory Value: " + money.format(total));
    }

}// end class BookStore