Dynamic input in ArrayList

Question

I am trying to create an ArrayList in which you can add input that is non-fixed, so you can add input later. Currently I have two issues:

the elements of the ArrayList aren't being printed.
I can only input one element, instead of an infinite amount.

Thanks

Code:

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    ArrayList<String> shopList = new ArrayList<>();
    while (true) {
        System.out.println("Enter an item: ");
        String item = sc.nextLine();
        shopList.add(item);
    }
    System.out.println("The Grocery List: " +shopList);
    sc.close();
}

The loop is running forever, so the println list never get executed. — LHA, Mar 06 '23 at 19:10

score 0 · Answer 1 · answered Mar 06 '23 at 19:37

You should code to an interface. ArrayList is the implementation. List is the interface.

You have an infinite loop. You need to decide on how to terminate the loop, otherwise code after the loop will not get executed.

In fact, when I copied your code to my Eclipse IDE, it flagged the following line of the code as Unreachable code

System.out.println("The Grocery List: " +shopList);

In the below code, I decided that simply hitting ENTER will terminate the loop.

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

public class ShopList {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        List<String> shopList = new ArrayList<>();
        while (true) {
            System.out.print("Enter an item (or just hit 'ENTER' to quit): ");
            String item = sc.nextLine();
            if (item.isEmpty()) {
                break;
            }
            else {
                shopList.add(item);
            }
        }
        System.out.println("The Grocery List: " +shopList);
        sc.close();
    }
}

Output from a sample run:
(Note that the second last entry was the TAB key and in the last entry, I hit the ENTER by itself which meant that item was an empty string.)

Enter an item (or just hit 'ENTER' to quit): s
Enter an item (or just hit 'ENTER' to quit): %
Enter an item (or just hit 'ENTER' to quit): mvosp[5rt04j89w
Enter an item (or just hit 'ENTER' to quit): *&^$^&$ghdtr d df
Enter an item (or just hit 'ENTER' to quit):    
Enter an item (or just hit 'ENTER' to quit): 
The Grocery List: [s, %, mvosp[5rt04j89w, *&^$^&$ghdtr d df,    ]

score 0 · Answer 2 · answered Mar 06 '23 at 20:06

This would be a great use case for a do...while() loop:

String item;
Scanner sc = new Scanner(System.in);

List<String> shopList = new ArrayList<String>();
do {
    System.out.print("Enter an item [Enter to quit]: ");
    item = sc.nextLine();
    if (!item.isEmpty()) {
      shopList.add(item);
    }
} while (!item.isEmpty());

System.out.println("The Grocery List: " + shopList);
sc.close();

Sample run:

Enter an item [Enter to quit]: pizza crust
Enter an item [Enter to quit]: pizza sauce
Enter an item [Enter to quit]: pepperoni
Enter an item [Enter to quit]: cheese
Enter an item [Enter to quit]: 
The Grocery List: [pizza crust, pizza sauce, pepperoni, cheese]

Dynamic input in ArrayList

2 Answers2