题目的主要信息：

• 有三个客户对象，将三个客户对象存入集合中，并将其按照消费总额从高到低排序

具体做法：

排序部分我们调用Collections类的sort函数，sort函数可以对List进行排序，但是因为我们这是有姓名和消费总额的集合，无法直接排序，我们要在其类中重载比较方法，实现消费额大的在前小的在后。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Customer customer1 = new Customer("小明",scanner.nextInt());
        Customer customer2 = new Customer("小军",scanner.nextInt());
        Customer customer3 = new Customer("小红",scanner.nextInt());
        List<Customer> customers = new ArrayList<>();
        customers.add(customer1);
        customers.add(customer2);
        customers.add(customer3);
        Collections.sort(customers); //排序函数
        System.out.println(customers); //输出
    }
}

class Customer implements Comparable<Customer>{
    private String name;
    private int consumption;

    public Customer(String name, int consumption) { //构造方法
        this.name = name;
        this.consumption = consumption;
    }

    @Override
    public String toString() { //构成字符串输出
        return "Customer{" +
                "name='" + name + '\'' +
                ", consumption=" + consumption +
                '}';
    }
    public int compareTo(Customer other){ //重载比较方法
        return other.consumption - this.consumption; //大的在前小的在后
    }
}

复杂度分析：

• 时间复杂度：$O(1)O(1)$，三个对象，常数时间实现排序和输出
• 空间复杂度：$O(1)O(1)$，常数空间