Creating a certain number of linked lists determined by user's entry

Question

I am a student, and i'm stuck here. I'm supposed to create multiple linked lists, the number of which is determined by user's entry. I thought of using a while loop, but i'm not sure how to name the lists differently like that. Help is appreciated.

    counter = 0;

    while (counter < userEntry){
    LinkedList <String> list (counter +1) = new LinkedList <String> ();
    counter++
    }

like the (counter +1) part is wrong and it gives a red line beneath it — newtoprogramming, Sep 23 '20 at 17:49
Why would you create multiple linked lists and not STORE them somewhere. As it is, those linked lists will simply get garbage collected when the while loop exits. Is there more to the assignment description?... — Idle_Mind, Sep 23 '20 at 18:01
Well, i'm given a file of students' names and i'm supposed to divide them into n groups (however many the user wants), and each group should have their names in a linked list — newtoprogramming, Sep 23 '20 at 18:03
That's great extra info. So you need to store your Linked Lists that you're creating outside the while loop so you can access them afterwards. You could store them in an array, or possibly a List of Lists? — Idle_Mind, Sep 23 '20 at 18:06
oh. i thought i could still access them if i created them in the while loop to make the process shorter — newtoprogramming, Sep 23 '20 at 18:08

Tharindu Sathischandra · Answer 1 · 2020-09-23T18:11:23.867

There are few syntax errors in your code.

First the counter did not have a data type.
userEntry variable is not defined.
no semicolon at counter++

So, I editted your code snippet. Is this what you needed to do?

public static void main(String[] args) {
    int counter = 0;
    int userEntry = 4;

    while (counter < userEntry){
       LinkedList <String> list = new LinkedList<String> ();
       counter++;
    }
}

But as you are trying to create multiple linked lists, one option is to create an array of linked lists.

public static void main(String[] args) {
    int counter = 0;
    int userEntry = 4; // example

    LinkedList[] listsArray = new LinkedList[userEntry];

    while (counter < userEntry){
      listsArray[counter] = new LinkedList<String> ();
      counter++;
    }
  }

Or as you are familiar with LinkedLists, you can create a list of LinkedLists.

public static void main(String[] args) {
    int counter = 0;
    int userEntry = 4; // example

    List<LinkedList<String>> listOfLinkedLists = 
    new LinkedList();

    while (counter < userEntry){
    LinkedList <String> list = new LinkedList<String> ();
      listOfLinkedLists.add(list);
      counter++;
    }
  }

I think what you are stucked at is this.

i'm not sure how to name the lists differently

If you are trying to create variable names at runtime, it will be not an easy task. You can take a look at this SO question too: Assigning variables with dynamic names in Java. But, the better way is to use use an array or a collection like List etc. as I mentioned above.

tysm, yes but i wanted to create more than one linked list within the same loop. that's why i added the (counter+1) so when the counter is zero, the name would be list(counter+1) so it would be named list1, and so on — newtoprogramming, Sep 23 '20 at 18:05

score 0 · Answer 2 · answered Sep 23 '20 at 17:58

It seems that based on the comments, you are supposed to do counter++ instead of counter + 1.
counter++ increments counter by one, while counter + 1 only adds 1 to counter and doesn't change the value of counter.

Also, you should store the LinkedLists in an ArrayList where you can get the user input and use a loop to add the number of LinkedLists you want into the ArrayList, then use ArrayList.get(counter) in your loop.

You can also use a for-each loop to loop through the LinkedLists in the ArrayList so you don't have to use a counter. Additionally, you can use a for loop if you need to use the counter in your loop. There are many ways to do this, hope my solution helps you.

Creating a certain number of linked lists determined by user's entry

2 Answers2