Question

I’m trying to make a custom linked list, so far I’ve figured out how to make the general structure and the two easiest methods (insertFirst and deleteFirst). The next thing I want to do is make a get method that takes the index of a link and then returns the string at that location. I don’t have any index or address assigned to each link, so I don’t see how to refer to a specific location in my linked list. I see that if I write first.next I get the second item, and first.next.next I get the third item.. But I need to figure out how to make my index parameter (the one passed into the get method) correlate with the proper location in my list. How can I do this?

Here’s my code:

Test code:

 class LinkedListTest {
    public static void main(String[] args)
    {
        LinkedList list = new LinkedList();
        
        list.insertFirst("cat");
        list.insertFirst("dog");
        list.insertFirst("fish");
        list.insertFirst("cow");
        list.insertFirst("horse");
        list.insertFirst("pig");
        list.insertFirst("chicken");
        
        System.out.println(list.get(1));
        
    }
}

My class:

public class LinkedList
{
    private Link first;
    
    
    public LinkedList()
    {
        first = null;
    }
    
    public void insertFirst(String word)
    {
        Link link = new Link(word);
        link.next = first;
        first = link;
    }
    
    public String deleteFirst()
    {
        Link temp = first;
        first = first.next;
        return temp.toString();
    }
    
    public String get(int index)
    {
        // the following is just to show that I can access different links
        // by adding more .next's after first--- but i need a way to access
        // the correct link based on the index passed in
        
        // String second = first.next.item;
        String third = first.next.next.item;
        // String fourth= first.next.next.next.item
        
        return third;
    }
    
}



public class Link
{
    public String item;
    public Link next;
    
    
    //Link constructor
    public Link(String theItem)
    {
        item = theItem;
    }
}

Answer 1

Assuming that get(0) returns you the first element:

If you want to put this method inside public class LinkedList:

    public String get(int index)
    {
        assert( index >= 0 )
        Link current = this.first;
        while (index > 0) {
            index--;
            current = current.next;
            // Check to see if this is out of bounds of the links
            if (current == Null) {
                // Since you are returning a String, you can also return
                // some kind of a flag to say that the index is out of bounds
                return Null;
            }
        }
        return current.item;       
    }

Alternatively, you can also implement this inside public class Link:, but this is not advisable since it wastes space on your call stack:

    public String get(int index)
    {
        assert ( index >= 0 )
        if ( index == 0 ) {
            return this.item;
        } else {
            index--;
            if ( next == null ) {
                return Null;
            }
            return next.get(index)
        }
    }

and inside public class LinkedList:

    public String get(int index)
    {
         return first.get(index);
    }

Hope this helps!