Printing an array list using ListIterator

Question

I am trying to print from an ArrayList using an ListIterator, i'm pretty sure i'm doing it wrong because it's not working but I don't know how to fix it. All so the line that grabs the part number isn't working, not sure why ;P. Any help is always appreciated :).

package invoice;
import static java.lang.System.out;

import java.util.*;

public class InvoiceTest {


    public static void print(){

    }

    public static void main (String args[]) {

        Scanner imput = new Scanner (System.in);
        ArrayList lInvoice = new ArrayList() ;
        int counter = 0;
        int partCounter;

        out.println("Welcome to invoice storer 1.0!");
        out.println("To start please enter the number of items: ");
        partCounter = imput.nextInt();


        while (counter < partCounter){
            counter++;
            out.println("Please enter the part number:");   
            Invoice invoice1 = new Invoice(); //Makes invoice 1 use the invoice class
            String partNumber = imput.nextLine();// sets part number to the next imput
            //invoice1.setPartNumber(partNumber);// Sets it to the private variable in invoice.java
            lInvoice.add(partNumber);

            out.println("Please enter in a discription of the part: ");
            String partDis = imput.nextLine();
            //invoice1.setPartDis(partDis);
            lInvoice.add(partDis);

            out.println ("Please enter the number of items purchased: ");
            int quanity = imput.nextInt();
            //invoice1.setQuanity(quanity);
            lInvoice.add(quanity);

            out.println ("Please enter the price of the item:");
            double price = imput.nextDouble();
            //invoice1.setPrice(price);
            lInvoice.add(price);

        }

        ListIterator<String> ltr = lInvoice.listIterator();
        while(ltr.hasNext());
        out.println(ltr.next());
    }
}

What's the error you get for the invoice part number; it looks like it could work, assuming Invoice has a `public void setPartNumber(String partNumber)` — Gus, May 22 '13 at 21:25
You should remove the `;` after `while(ltr.hasNext())`, it is just an empty statement witch consumes your while loop. — A4L, May 22 '13 at 21:28
Does this answer your question? [Ways to iterate over a list in Java](https://stackoverflow.com/questions/18410035/ways-to-iterate-over-a-list-in-java) — Aswin Prasad, Dec 02 '19 at 10:47

Alexis C. · Answer 1 · 2013-05-22T22:31:48.030

5

There is some other errors in your program.

First, you shoud add a type to your ArrayList. Since you're trying to add int, double and String, I recommend you to create an ArrayList<Object> lInvoice = new ArrayList<Object>() ;

Then just loop with your iterator :

ListIterator<Object> ltr = lInvoice.listIterator();
       while(ltr.hasNext()){
           out.println(ltr.next()); 
       }

edited May 22 '13 at 22:31

answered May 22 '13 at 21:22

Alexis C.

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@Blank1268 and for fun and giggles, did you know the `foreach` operator uses iterators behind the scenes? Try out `for (Object o : lInvoice) { out.println(o); }` – Porkbutts May 22 '13 at 21:55

score 3 · Answer 2 · answered May 22 '13 at 21:17

3

You actually don't print anything within the while loop, because your println() callback is out of the scope of the loop. Fix it like this:

ListIterator<String> ltr = lInvoice.listIterator();
while(ltr.hasNext()) {
   out.println(ltr.next());
}

answered May 22 '13 at 21:17

Konstantin Yovkov

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This wasn't my question, but I have to ask - how does the ListIterator work if it is parameterized to accept Strings when some of the things being added to the ArrayList it traverses are ints. Are they automatically parsed? – Andrew Martin May 22 '13 at 21:21
Since you have `ArrayList()` which is not parametrized, they are all Objects, actually. And when you print them, the `toString()` method is invoked. – Konstantin Yovkov May 22 '13 at 21:23
1

@kocko If you try to run the code, you will get a `ClassCastException` when looping with the `iterator` because the iterator expects objects as String (as its parametized). – Alexis C. May 22 '13 at 21:25
since the list in raw the `listIterator` has also to be raw for casting to work – A4L May 22 '13 at 21:27
1

@ZouZou: That's what my initial thought was. Should really have just run the code to check for myself! Thanks. – Andrew Martin May 22 '13 at 21:28

score 1 · Accepted Answer · answered May 22 '13 at 21:50

Putting on my psychic debugger hat, I'm guessing you meant to print out a line-item invoice. I'm making some assumptions about the contents of Invoice.java, but I'm guessing the below code is what you really wanted:

    Scanner imput = new Scanner(System.in);
    ArrayList<Invoice> lInvoice = new ArrayList<Invoice>();
    int counter = 0;
    int partCounter;

    out.println("Welcome to invoice storer 1.0!");
    out.println("To start please enter the number of items: ");
    partCounter = imput.nextInt();
    imput.nextLine();//skips the rest of the line (carriage return)

    while (counter < partCounter) {
        counter++;
        out.println("Please enter the part number:");
        Invoice invoice1 = new Invoice(); // Makes invoice 1 use the invoice
                                            // class
        String partNumber = imput.nextLine();// sets part number to the next
                                                // imput
        invoice1.setPartNumber(partNumber);// Sets it to the private
                                            // variable in invoice.java

        out.println("Please enter in a discription of the part: ");
        String partDis = imput.nextLine();
        invoice1.setPartDis(partDis);

        out.println("Please enter the number of items purchased: ");
        int quanity = imput.nextInt();
        imput.nextLine();
        invoice1.setQuanity(quanity);

        out.println("Please enter the price of the item:");
        double price = imput.nextDouble();
        imput.nextLine();
        invoice1.setPrice(price);
        lInvoice.add(invoice1);
    }

    ListIterator<Invoice> ltr = lInvoice.listIterator();
    while (ltr.hasNext()) {
        Invoice next = (Invoice)ltr.next();
        out.println(next.getPartNumber()+"\t"+next.getPartDis()+"\t"+next.getPrice()+"\t"+next.getQuanity());
    }

Interesting changes:

I'm using a list of Invoice instead a list of strings, and then printing out each one
Scanner.nextInt() will leave the carriage return from its input, so you have to call nextLine() to clear it, or you'll miss the input you really wanted.

Printing an array list using ListIterator

3 Answers3