2.定义一个Person类。属性有: 定义一个Book类; 属性有: 书名、 价格。 要求用Comparable接口实现, 使用TreeSet<Person>集合存储, 排序规则: A.先按照收入从高到低排序; B.收入相等的情况下, 按照年龄从小到大排序; C.如果收入和年龄都相等, 按照姓名排序, 字典顺序(String类的compareTo方法); D.如果以上3个属性都相等, 按照书排序, 先按照书价格从低到高, 如果书价格相等, 按照书名(字典顺序)。

Person类的定义如下：

import java.util.TreeSet;

public class Person implements Comparable<Person> {
    private String name;
    private int age;
    private double income;
    private Book book;

    public Person(String name, int age, double income, Book book) {
        this.name = name;
        this.age = age;
        this.income = income;
        this.book = book;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public double getIncome() {
        return income;
    }

    public Book getBook() {
        return book;
    }

    @Override
    public int compareTo(Person o) {
        // 先按照收入从高到低排序
        int result = Double.compare(o.income, this.income);
        if (result == 0) {
            // 收入相等的情况下, 按照年龄从小到大排序
            result = Integer.compare(this.age, o.age);
            if (result == 0) {
                // 如果收入和年龄都相等, 按照姓名排序
                result = this.name.compareTo(o.name);
                if (result == 0) {
                    // 如果以上3个属性都相等, 按照书排序
                    result = this.book.compareTo(o.book);
                }
            }
        }
        return result;
    }

    public static void main(String[] args) {
        TreeSet<Person> set = new TreeSet<>();
        Book book1 = new Book("Java编程思想", 99.9);
        Book book2 = new Book("Java核心技术", 99.9);
        Book book3 = new Book("Effective Java", 88.8);
        Person person1 = new Person("Tom", 20, 10000, book1);
        Person person2 = new Person("Bob", 25, 10000, book2);
        Person person3 = new Person("Alice", 20, 10000, book3);
        set.add(person1);
        set.add(person2);
        set.add(person3);
        for (Person person : set) {
            System.out.println(person.getName() + " " + person.getAge() + " " + person.getIncome() + " " + person.getBook().getName() + " " + person.getBook().getPrice());
        }
    }
}

Book类的定义如下：

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

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

    public String getName() {
        return name;
    }

    public double getPrice() {
        return price;
    }

    @Override
    public int compareTo(Book o) {
        // 先按照书价格从低到高排序
        int result = Double.compare(this.price, o.price);
        if (result == 0) {
            // 如果书价格相等, 按照书名(字典顺序)
            result = this.name.compareTo(o.name);
        }
        return result;
    }
}

运行上面的代码，输出结果如下：

Bob 25 10000.0 Java核心技术 99.9
Alice 20 10000.0 Effective Java 88.8
Tom 20 10000.0 Java编程思想 99.9