有题不会家人们祝我一臂之力

西瓜1.5一个
如果买10个以上 打9折
如果买20个以上 打7折
班长买了x个西瓜，计算价格

Scanner sc = new Scanner(System.in);
int x = sc.nextInt();
double y = 0;
if(x<10) y = 1.5*x;
else if(x>=10 && x <20) y = 1.5*x * 0.9;
else y = 1.5*x*0.7;
System.out.println(y);

上课不听

package javatest;
import java.util.Scanner;
public class BuyWaterMelon {
public static void main(String[] args) {
while(true) {
System.out.print("请输入购买西瓜数：");
Scanner sc = new Scanner(System.in);
int num = sc.nextInt();
double price = 1.5*num;
if(num > 20)
price *= 0.7;
else if(num > 10)
price *= 0.9;
else price *= 1;
System.out.println("西瓜总价：" + price);
}
}
}

public static void main(String[] args) {
        int num = 25;
        double price = 1.5;
        double count = countMoney(num,price);
        System.out.println("班长买了"+num+"个西瓜，总价格为："+count+"元。");

    }

    public static double countMoney(int num,double price){
        //num为购买数量,price为西瓜单价
        if(num <=10){
            price =  num*price;
        }else   if(num<=20){
            price = num*price*0.9;
        }else{
            price = num * price * 0.7;
        }
        return price;
    }