java中如何返回到代码的开头

Question

我目前正在用java在初学者编程课上做一个项目。该项目涉及制造自动售货机。本质上，自动售货机会询问您想要什么商品，然后它会向您要钱。每当有人选择某件商品时，该商品的数量就会减少一个。我想要做的是让它在某个商品缺货（数量为0）时，代码返回到开头并再次询问您想要什么商品。我也想这样做，如果有人输入无效数字，代码也会重新启动。我该怎么做？这是代码。

import java.util.Scanner;

public class VendingMachine {

public static void main(String[] args) {

    Scanner user_input = new Scanner(System.in);

    int potatoChips = 0;

    int cookies = 3;

    int candies = 4;

    int quarters;

    int dimes;

    int nickels;

    System.out.println("Select the number for the item you would like");

    System.out.println("For Potato Chips, Enter 1");

    System.out.println("For Cookies, Enter 2");

    System.out.println("For Candies, Enter 3");

    int itemSelection = user_input.nextInt();

        if (itemSelection == 1) {

            if (potatoChips > 0) {

                potatoChips = potatoChips - 1;

                System.out.println("You chose potato chips.");

                System.out.println("That will be $1.25");

                System.out.println("How many quarters do you have?");

                quarters = user_input.nextInt();

                System.out.println("How many dimes do you have?");

                dimes = user_input.nextInt();

                System.out.println("How many nickels do you have?");

                nickels = user_input.nextInt();

                int nickelsToPennies = (nickels * 5);

                int dimesToPennies = (dimes * 10);

                int quartersToPennies = (quarters * 25);

                int pennies = (nickelsToPennies + dimesToPennies + quartersToPennies);

                if (pennies < 125) {

                    System.out.println("You have not entered enough money. Have a great day.");

                }

                else if (pennies == 125 ) {

                    System.out.println("Here is your snack. Have a great day");

                }

     

Answer 1

您必须使用连续while循环。就像是：while(true) {&nbsp; &nbsp; //collect user input&nbsp; &nbsp; //process}这样，当它完成处理您的用户请求时，它会循环回到开头。如果您想在未完成时停止它，例如输入错误，您可以使用continue关键字来停止当前循环并返回到开头。break将使您退出整个 while 循环并结束代码。