Linked List Constructor with initial value

Question

I'm working on a Linked List project, and i'm having a great trouble with the constructor.

i already implemented the default constructor (creates empty list. AKA data = null, size = 0) but the other constructor is really confusing me !!!!

i want to implement a constructor that creates a linked list with valueS/elementS in it (String[]). My first thought was "Piece of cake, all i have to do is :

Use the default constructor to create an empty linked list
Use a for-each loop within a for loop. The for-each loop is to iterate the string array and add them to my empty linked list. The for loop is needed to keep a track of the index."

Here is my Code:

public LinkedList(String[] data)
{
    LinkedList l = new LinkedList();

    for (int i = 0; i <= data.length; i++)
    {

        for (String d : data)
        {
            l.add(d, i);
            i++;
        }

    }
}

i tested my code by using this constructor but it does not work. i know there is a silly mistake somewhere but my logic/mind is blind to see it.

@sol4me Yes man, i should've used this(); instead of using the actual constructor — Smartian
– Smartian, Commented Dec 20, 2014 at 3:51
@PM77-1 i created an array of strings, then i created a linked list using my code, then i tried to locate (get method) and check (size method) and they didn't add up. I needed two loops to keep track of the index and to traverse through the array. — Smartian
– Smartian, Commented Dec 20, 2014 at 3:58

Mshnik · Accepted Answer · 2014-12-20 03:09:41Z

2

Well you're not really referring to "this" anymore in the constructor you've written. You create a linked list l and modify that one, but you never actually work on "this". Also I agree with the others, the second for loop is unnecessary.

This also lets you use this(), which is a cool functionality to get to know. Helps you keep your code DRY and bug free.

public LinkedList(String[] data){
    this(); //Call the default constructor to set up default properties
    for (String d : data){
        add(d); //Call on this
    }
}

answered Dec 20, 2014 at 3:09

Mshnik

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1 Comment

Smartian Over a year ago

YOU SIR, deserve a pint of your favourite lager on me. I'm so familiar with "this" function, as a matter of fact i've been using it through most (90%) of my other methods. but as i said before "i'm blind to see it" Thank you, (even though i fixed it, i have to deal with other "newborn" bugs.

codelion · Accepted Answer · 2014-12-20 02:16:11Z

1

You need to change the arguments to the add method, it expects the index to be the first argument. See http://docs.oracle.com/javase/7/docs/api/java/util/LinkedList.html#add(int,%20E).

    for (String d : data)
    {
        l.add(i, d);
        i++;
    }

answered Dec 20, 2014 at 2:16

codelion

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1 Comment

Smartian Over a year ago

That's totally true, but my API writer described the method add as public void add(java.lang.String data, int index). The parameter is data then index.

kuriouscoder · Accepted Answer · 2014-12-20 02:50:45Z

0

Another way of doing this would be to just add l.add(d) in the loop. With this new elements are guaranteed to be inserted at the end of the list.

I would use l.add(i, d) when I want to insert specifically at a given location.

answered Dec 20, 2014 at 2:50

kuriouscoder

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Comments

Jared Rummler · Accepted Answer · 2014-12-20 04:37:44Z

0

Does your class extend LinkedList? If so, here is what I would do:

public class MyLinkedList extends LinkedList<String> {

    ...

    public MyLinkedList(String... array) {
        super();
        if (array != null && array.length > 0) {
            for (String s : array) {
                add(s);
            }
        }
    }

    ...

}

It isn't a great idea to extend LinkedList. If you want an easy way to create a new LinkedList with elements use the following method:

public static <E> LinkedList<E> newLinkedList(
        @SuppressWarnings("unchecked") final E... elements) {
    final LinkedList<E> list = new LinkedList<E>();
    Collections.addAll(list, elements);
    return list;
}

....

LinkedList<String> yourList = newLinkedList("foo", "bar", "baz");

edited Dec 20, 2014 at 4:37

answered Dec 20, 2014 at 4:15

Jared Rummler

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