Thread: List methods add(int k, Data data), set(int k, Data data), remove(int k)

Hello,I've recently started studying Java, and I've encountered some problems with lists. There's pretty much close to none information about this where I am studying at, so I would be really grateful if someone could create these 3 methods for me, since I would have a great example to use later on. I have to create the 3 methods add(int k, Data data), set(int k, Data data), remove(int k) . Here's the code I have : ( although I think the main part needed for these methods is:
private Node<Data> first;
private Node<Data> last;
private Node<Data> current;

package studijosKTU;
 
public class ListKTU<Data> implements ListADT<Data> {
 
    private Node<Data> first;   
    private Node<Data> last;    
    private Node<Data> current; 
    private int size;           
    /**
     * Constructs an empty list.
     */
    public ListKTU() {
    }
    public boolean add(Data data) {      // adds an element to the end of the list
        if(data==null) return false;        // doesnt take null objects
        if (first == null) {
            first = new Node<Data>(data, first);
            last = first;
        } else {
            Node<Data> e1 = new Node(data, null);
            last.next = e1;
            last = e1;
        }
        size++;
        return true;
    }
    public boolean add(int k, Data data){  // inserts before k position
        if(data==null) return false;       // doesnt take null bojects
        if (k<0||k>=size)return false;     // returns null if k isn't correct.
        throw new UnsupportedOperationException
                ("Have to create this one");
 
    public int size() {     
        return size;
    }
    public boolean isEmpty() {      
        return first == null;
    }
    public void clear() {
        size = 0;
        first = null;
        last = null;
        current = null;
    }
    public Data get(int k){           // returns the value of k
        if (k<0||k>=size)return null;
        current=first.findNode(k);   
        return current.element;
    }
    public Data set(int k, Data data){   // sets the value of element k
        if(data==null) return null;     
        throw new UnsupportedOperationException
                ("Have to create this one");
    }
    public Data getNext(){       
        if(current==null) return null;
        current=current.next;
        if(current==null) return null;
        return current.element;
    }
    public Data remove(int k) {
       throw new UnsupportedOperationException
                ("Have to create this one");
    }
 
class Node<Data> {          // class that ensures incapsulation
    public Data element;   
    public Node<Data> next; 
 
    Node(Data data, Node<Data> next) { 
        this.element = data;
        this.next = next;
    }
    public Node<Data> findNode(int k){ 
        Node<Data> e=this;
        for(int i=0;i<k;i++){
           e=e.next;
        }
        return e;
    }
}
}