再加个循环，判断购买完成之后输入是Y还是N就可以了应该（没有编译环境，可能有bug，可以参考）

import java.util.Scanner;
public class HelloWorld {
    public static void main(String []args) {
        Scanner sc = new Scanner(System.in);
        
           System.out.println("1");
        System.out.println("2");
        System.out.println("3");
        System.out.println("4");
        System.out.println("5");
        
        double sum = 0;
        double a = 8.8;
        double b = 10.0;
        double c = 18.8;
        double d = 12.5;
        double e = 15.5;
        
        int s,m;
        System.out.println("购买的物品是:");
        s = sc.nextInt();
        System.out.println("购买的数量是:");
        m = sc.nextInt();
        switch(s){
            case 1:
                System.out.println("购买1");
                sum += a*m;
                break;
            case 2:
                System.out.println("购买2");
                sum += b*m;
                break;
            case 3:
                System.out.println("购买3");
                sum += c*m;
                break;
            case 4:
                System.out.println("购买4");
                sum += d*m;
                break;
            case 5:
                System.out.println("购买5");
                sum += e*m;
                break;
        }
        System.out.println("最终消费"+sum+"元");
    }
}