Question

基本上，我正在blueJ中创建购物应用程序，但我偶然发现了一个问题。我已经做出了If语句，该语句允许用户1.购物2.检查购物篮3.结帐，当我输入1进行购物并将商品添加到购物清单时，我似乎无法退出循环内。有关如何解决此问题的想法？

import java.util.Scanner;
import java.util.ArrayList;
public class List
{
    public String itemsList;
    ArrayList<String> alist=new ArrayList<String>();
    public List()
    {
    }

    /*public String itemList()
    {
    System.out.println("1. Veg");
    System.out.println("2. sweets");
    System.out.println("3. drink");
    System.out.println("4. toiletries");
    return itemsList;
    }
     */

    public void Shopping()
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("1. do shopping");
        System.out.println("2. check basket");
        System.out.println("3. go to checkout");
        String choice1 = sc.next();

        if(choice1.equals("1"))
        {
            boolean stop = false;
            while(!stop){
                Scanner scanner = new Scanner(System.in);
                System.out.println("1. Veg");
                System.out.println("2. sweets");
                System.out.println("3. drink");
                System.out.println("4. toiletries");
                System.out.println("5. alcohol");
                System.out.println("6. go back");
                String choice = scanner.next();
                if(choice.equals("1"))
                {
                    System.out.println("Veg has been added to your basket");
                    alist.add("veg");
                }else if(choice.equals("2"))
                {
                    System.out.println("sweets have been added to your basket");
                    alist.add("veg");
                }else if(choice.equals("3"))
                {
                    System.out.println("drinks have been added to your basket");
                    alist.add("veg");
                }else if(choice.equals("4"))
                {
                    System.out.println("toiletries have been added to your basket");
                    alist.add("veg");
                }else if(choice.equals("5"))
                {
                    Scanner scanner1 = new Scanner(System.in);
                    System.out.println("Check ID if age is under 25");
                    System.out.println("How old are you?");
                    int underAge = scanner1.nextInt();
                    int i;
                    i = 18;
                    if(underAge < i)
                    {
                        System.out.println("You are not old enough to buy alcohol");
                    } else{
                        System.out.println("Alcohol has been added to your basket");
                        alist.add("veg");
                    }
                }else if(choice.equals("6"))
                {

                }

            }
        }else if(choice1.equals("2")){
            System.out.println(alist);
        }else if(choice1.equals("3")){
            System.out.println("Are you sure you want to checkout? ");
            System.out.println("1. No");
            System.out.println("2. Yes");
            Scanner scanner3 = new Scanner(System.in);
            String checkout = scanner3.next();
            if(checkout.equals("1"))
            {
                return;
            } else {
                System.out.println("test");
            }

        }
    }
}

Answer 1

    int num=1;
    if(num==1){
        while(num<10){
            num++;
            if(num==5){
                break;
            }
        }
        System.out.println(num);
    }

输出为5

这是因为 break; 语句脱离了它可以找到的最内层循环

Answer 2

1。我建议您对要执行的每个操作使用单独的方法。这样，您可以轻松地返回到代码的任何部分，因为实际上这将是方法的返回。 2.您不必启动扫描仪很多次，而一开始只需启动一次。 3.您可以通过将常见或相似的操作组合为一种方法来优化代码。例如，您的代码可以通过以下方式修改：

import java.util.ArrayList;
import java.util.Scanner;

public class List{

    static ArrayList<String> alist = new ArrayList<String>();
    static Scanner sc = new Scanner(System.in);
    static String choice;

public static void main(String args[]){
    mainMenue();
}

private static void mainMenue() {
     System.out.println("1. do shopping \n2. check basket \n3. go to checkout");
     choice = sc.next();
     if(choice.equals("1")) shoppingMenue();
     else if(choice.equals("2")) checkingMenue();
     else if(choice.equals("3")) checkoutMenue();
}

private static void checkoutMenue() {
    System.out.println("Are you sure you want to checkout? \n1. No \n2. Yes");
    choice = sc.next();
    if(choice.equals("1"))return;
    else System.out.println("test");
}

private static void checkingMenue() {
    System.out.println(alist);
}

private static void shoppingMenue() {
    boolean stop = false;
    while(!stop){
        System.out.println("1. Veg \n2. sweets \n3. drink \n4. toiletries \n5. 
alcohol \n6. go back");
        choice = sc.next();
        if(choice.equals("1")) printAndSave(1);
        else if(choice.equals("2")) printAndSave(2);
        else if(choice.equals("3")) printAndSave(3);
        else if(choice.equals("4")) printAndSave(4);
        else if(choice.equals("5")) {
            System.out.println("Check ID if age is under 25 \nHow old are you?");
            if(sc.nextInt() < 18) System.out.println("You are not old enough to buy 
alcohol");
            else printAndSave(5);
        }
        else if(choice.equals("6")) mainMenue();
    }
}

private static void printAndSave(int i) {
    ArrayList <String> textList = new ArrayList <>(6);
    textList.add(0, "");
    textList.add(1, "Veg has been added to your basket");
    textList.add(2, "Sweets have been added to your basket");
    textList.add(3, "Drinks have been added to your basket");
    textList.add(4, "Toiletries have been added to your basket");
    textList.add(5, "Alcohol has been added to your basket");

    System.out.println(textList.get(i));
    alist.add("veg");
    }
}

如何离开if语句内的while循环并继续执行if语句？

2 个答案: