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) {

    //collect user input

    //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。