"应付金额：" + price + "元。"

import java.util.Scanner;

public class Shopping {
public static void main(String[] args) {
double price = 580;
double discount = 0.8;
Scanner sc = new Scanner(System.in);
System.out.print("输入要购买商品的数量：");
int number = sc.nextInt();
sc.close();
Shopping shopping = new Shopping();
if (number == 1) {
shopping.pay(number, price);
} else {
shopping.pay(number, price, discount);
}
}

public void pay(int account, double price) {
    System.out.println("应付金额：" + price + "元。");
}

public void pay(int account, double price, double discount) {
    System.out.println("应付金额：" + (account * price * discount) + "元。");
}

}