用Java编程定义一个Book类并能根据价格进行比较。创建一个泛型集合存放图书，对图书进行排序并输出。

好的，以下是Java代码实现：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class Book implements Comparable<Book> {
    private String title;
    private double price;

    public Book(String title, double price) {
        this.title = title;
        this.price = price;
    }

    public String getTitle() {
        return title;
    }

    public double getPrice() {
        return price;
    }

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

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

    @Override
    public int compareTo(Book book) {
        if (this.price > book.price) {
            return 1;
        } else if (this.price < book.price) {
            return -1;
        } else {
            return 0;
        }
    }

    public static void main(String[] args) {
        ArrayList<Book> books = new ArrayList<>();
        books.add(new Book("Java Programming", 39.99));
        books.add(new Book("Python Programming", 29.99));
        books.add(new Book("C++ Programming", 49.99));
        books.add(new Book("Data Structures and Algorithms", 59.99));
        books.add(new Book("Database Systems", 69.99));

        Collections.sort(books);
        System.out.println("Sorted by price (ascending order):");
        for (Book book : books) {
            System.out.println(book.getTitle() + " - $" + book.getPrice());
        }

        Collections.sort(books, new Comparator<Book>() {
            @Override
            public int compare(Book book1, Book book2) {
                return book2.getTitle().compareTo(book1.getTitle());
            }
        });
        System.out.println("\nSorted by title (descending order):");
        for (Book book : books) {
            System.out.println(book.getTitle() + " - $" + book.getPrice());
        }
    }
}

在这个例子中，我们定义了一个`Book`类，它有一个`title`属性和一个`price`属性，以及一个比较价格的`compareTo`方法。我们还创建了一个`ArrayList`来存放书籍，然后使用`Collections.sort`方法对其进行排序。在第一次排序中，我们使用默认的价格比较方法来对图书进行排序（升序）。在第二次排序中，我们使用自定义的标题比较方法对图书进行排序（降序）。最后，我们打印出每个图书的标题和价格来验证排序是否正确。