为什么这个循环会回到开始？

Question

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

class SteppingStone4_Loops {

    public static void main(String[] args) {
       Scanner scnr = new Scanner(System.in);
       String recipeName = "";
       ArrayList<String> ingredientList = new ArrayList();
       String newIngredient = "";
       boolean addMoreIngredients = true;

       System.out.println("Please enter the recipe name: ");
       recipeName = scnr.nextLine();


       do {           
           System.out.println("Would you like to enter an ingredient: (y or n)");
           String reply = scnr.next().toLowerCase();

           /**The code should check the reply:
            *   "y" --> prompt for the ingredient and add it to the ingredient list;
            *   "n" --> break out of the loop;  
            *   anything else --> prompt for a "y" or "n"
            */

          while (true) {
             if (reply.equals("y")) {
               System.out.println("Enter ingredient name: "); 
               newIngredient = scnr.next();   
               ingredientList.add(newIngredient);
             break;
           }
             else if (reply.equals("n")) {
                System.out.println("Goodbye!");
                break;
             }

            else  
               break;
           }


            } while (addMoreIngredients);
           for (int i = 0; i < ingredientList.size(); i++) {
           String ingredient = ingredientList.get(i);
           System.out.println(ingredient);
       }
    }
}

When ran, the program returns this:

Please enter the recipe name:
Polenta
Would you like to enter an ingredient: (y or n)
y
Enter ingredient name:
Salt
Would you like to enter an ingredient: (y or n)
n
Would you like to enter an ingredient: (y or n)
5
Would you like to enter an ingredient: (y or n)

Why doesn't it break when reply = n? Why does it go back to the "Would you like to enter an ingredient"? Can someone pinpoint my mistake or perhaps suggest a different way? Thanks

Answer 1

Please note, you have 2 while loops

  else if (reply.equals("n")) {
            System.out.println("Goodbye!");
            break;
         }

The above condition will break out from inner while loop and outer while loop will still continue and that's why you are getting output "Would you like to enter an ingredient", which part of outer loop.

Since, in outer loop, you have below condition, which is set true and never seems to be changed.

while (addMoreIngredients)

So, before breaking out from inner loop, you could change addMoreIngredients to false

  else if (reply.equals("n")) {
        System.out.println("Goodbye!");
        addMoreIngredients = false;
        break;
     }

Just to let you know, you could also use label break instead.

Answer 2

while (addMoreIngredients);

This line always returns true. So your do loop keeps on looping.

I suggest setting a flag from inner loop for outerloop as well.

--edit----- lets get rid of inner loop, i think it should work fine. PS: right now i don't have access to a JRE. But i think it should work

do {           
           System.out.println("Would you like to enter an ingredient: (y or n)");
           String reply = scnr.next().toLowerCase();

             if (reply.equals("y")) {
               System.out.println("Enter ingredient name: "); 
               newIngredient = scnr.next();   
               ingredientList.add(newIngredient);
               continue;
           }
             else if (reply.equals("n")) {
                System.out.println("Goodbye!");
                break;
             }

            else {
            System.out.println("Invalid option!");
            continue;
            }   
 } while (addMoreIngredients);

Answer 3

Please check that you have nested loops and break statement in inner loop only break out from inner loop and you apply the second condition of the do-while loop on addMoreIngredients = true

break statment only break out the inner loop.

so it always runs because addMoreIngredients always true.

Answer 4

make addMoreIngredients is false

 else if (reply.equals("n")) {
            System.out.println("Goodbye!");
            addMoreIngredients = false;
            break;
         }