定义一个 Person 类。 属性有: 姓名、 收入、 年龄、 书(一本)。 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 类的代码如下：

import java.util.TreeSet;

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

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

    public String getName() {
        return name;
    }

    public int getIncome() {
        return income;
    }

    public int getAge() {
        return age;
    }

    public Book getBook() {
        return book;
    }

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

Book 类的代码如下：

public class 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;
    }
}

使用 TreeSet<Person> 集合存储的代码如下：

import java.util.TreeSet;

public class SortPerson {
    public static void main(String[] args) {
        TreeSet<Person> set = new TreeSet<>();
        set.add(new Person("Alice", 50000, 25, new Book("Java Programming", 80.0)));
        set.add(new Person("Bob", 60000, 30, new Book("Python Programming", 70.0)));
        set.add(new Person("Charlie", 50000, 20, new Book("C++ Programming", 80.0)));
        set.add(new Person("David", 50000, 25, new Book("JavaScript Programming", 60.0)));
        System.out.println(set);
    }
}

输出结果为：

[Person{name='Bob', income=60000, age=30, book=Book{name='Python Programming', price=70.0}}, 
Person{name='Alice', income=50000, age=25, book=Book{name='Java Programming', price=80.0}}, 
Person{name='David', income=50000, age=25, book=Book{name='JavaScript Programming', price=60.0}}, 
Person{name='Charlie', income=50000, age=20, book=Book{name='C++ Programming', price=80.0}}]