Basic LinkedList/Iterator programm terminates without explanation

Question

Could someone exlain to me why the following code results in the programm being terminated immediately? There's almost nothing to go by in the console or debug tab.

Thanks in advance!

@bowmore: Thank you, that was one error. However, when I add to the ListIterator instead, I'm getting an OutOfMemory: Java heap space exception.

package Buchalka1;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.ListIterator;

public class LinkedList2 {

    //--------------------------------------------------------------------------------------------------
    public static void main(String[] args)
    {
        LinkedList<String> letters = new LinkedList<String>();

        addInOrder(letters, "D");
        addInOrder(letters, "A");
        addInOrder(letters, "B");
        printList(letters);
    }
    //--------------------------------------------------------------------------------------------------
    public static void printList(LinkedList<String> list)
    {
        Iterator<String> iterator1 = list.iterator();
        while (iterator1.hasNext()) {
            System.out.println("Entry: " + iterator1.next());
        }
        System.out.println("-----------------------------------------------------");
    }
    //--------------------------------------------------------------------------------------------------
    public static void addInOrder(LinkedList<String> list, String newEntry)
    {
        ListIterator<String> listIterator1 = list.listIterator();

        while(listIterator1.hasNext()) {
            int comparison = listIterator1.next().compareTo(newEntry);
            if (comparison == 0) {
                // newEntry should not be added, because already present.
                System.out.println(newEntry + " is already part of the list.");
            } else if (comparison > 0) {
                // newEntry should be listed before the iterator's current entry.
                listIterator1.previous();
                listIterator1.add(newEntry);
            } else if (comparison < 0){
            }
        }
        listIterator.add(newEntry);
    }
    //--------------------------------------------------------------------------------------------------
}

Console:

Exception in thread "main" java.util.ConcurrentModificationException at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:966) at java.util.LinkedList$ListItr.next(LinkedList.java:888) at Buchalka1.LinkedList2.addInOrder(LinkedList2.java:34) at Buchalka1.LinkedList2.main(LinkedList2.java:15)

Debug:

terminated LinkedList2 [Java Application]
terminated, exit value: 1>D:\Programs\java\jdk1.8\bin\javaw.exe (17.12.2019, 16:14:44)

You add to the list directly, while still using the Iterator. Use the add on the iterator instead. — bowmore, Dec 17 '19 at 15:29

score 1 · Answer 1 · answered Dec 17 '19 at 15:31

In Java when you are iterating over a list, you should not edit the list you are iterating over.

In your case, you iterate over the LinkedList, and try to add things to it. Java tells you not to ever do this.

If I understand your code well enough, you want to add an item to the list, and make sure the list stays in the correct order. An alternative approach to this is to first add the item (unsorted) and then sort the list using Collections.sort().

This should help you get rid of that annoying error, and make your code a lot more concise and readable.

Basic LinkedList/Iterator programm terminates without explanation

1 Answers1